Immunology Exam 4

Effective vaccines have been developed against a number of deadly diseases, including viral diseases such as measles, mumps, polio, and smallpox, as well as several bacterial infections. However, there remain several important infectious diseases for which vaccines are currently lacking. One important aspect of developing effective vaccines against these pathogens is:

A clear understanding of the immune mechanisms required to eliminate the infection

Viruses utilize many different strategies to evade the immune response after infection. One strategy, illustrated in Figure Q13.25, is an effect on virus-infected cells.

A large DNA virus

While relatively rare, individuals with a homozygous deficiency in complement C1 activity have been identified, and >90% of them developed a lupus-like illness at a very young age. These individuals had significant kidney damage and damage to blood vessels in the central nervous system, both of which were associated with severe inflammation. A reasonable hypothesis to explain the development of the lupus-like disease in these patients is:

A role for the complement pathway in clearing apoptotic cells from the circulation

One HIV vaccine trial provided some small measure of hope for the development of an effective HIV vaccine. This vaccine, known as RV144, was administered to a high risk population in Thailand, and reduced new infections by ~30%. To address the mechanism of immune protection correlating with vaccine efficacy, a series of studies were performed. In one study, total IgG antibodies from four non-infected vaccinees were isolated and were mixed with HIV-infected cells plus peripheral blood lymphocytes from healthy unrelated donors. As a control, IgG antibodies were purified from four donors receiving the placebo, rather than the RV144 vaccine. Six hours later, lysis of the HIV-infected target cells was assessed, as shown in Figure Q13.40. The immune mechanism that correlates with protection based on these data is:

ADCC induced by NK cells

AIRE is a transcriptional regulator that promotes the expression of some 'tissue-specific' proteins in thymic stromal cells. This provides a means to induce central tolerance of developing T cells to these antigens. Patients with inactivating mutations in AIRE (a disease known as APECED) develop a range of symptoms, several of which involve autoimmune attack of exocrine glands. However, analysis of many patients with APECED reveals that some organs in the body are never attacked by autoimmune T cells in individuals with this syndrome, whereas other organs are commonly found to be destroyed in these patients. This targeted autoimmune response against a subset of tissues in APECED patients indicates:

AIRE likely regulates genes expressed in this subset of tissues, but not genes in other tissues.

Malaria is caused by protozoan parasites, Plasmodium falciparum and Plasmodium vivax. These pathogens are transmitted when an individual is bitten by a Plasmodium-infected mosquito. This route of transmission:

Allows the parasite to avoid the normal mechanisms blocking infections at barrier surfaces

GWAS data have identified multiple genes associated with autoimmune diseases. These data indicate the presence of polymorphisms in the gene sequence among the human population, where certain alleles are increased among patients with a particular autoimmune disease. One example is the gene encoding the IL-2R chain. Interestingly, several of the polymorphisms in this gene that are found to be increased in patients with multiple sclerosis do not alter the protein coding sequence, and therefore do not result in differences in the amino acid sequence of the IL-2R chain protein between healthy individuals and those with the disease-associated allele. Instead, it is likely that these allelic differences in the IL-2R chain locus:

Alter the levels of expression or cell-type specificity of the IL-2R chain protein

Administration of large quantities of non-specific IgG (known as IVIG) has been shown to be beneficial in the treatment of some autoimmune disease caused by autoantibodies. A mouse model of autoimmune thrombocytopenia has been developed, in which anti-platelet antibodies (anti-platelet Ab) are injected into mice, causing platelet destruction. When anti-platelet antibodies are injected, and at the same time recipient mice are treated with IVIG, disease severity is substantially reduced. The numbers of platelets per ml of blood in the recipient mice is quantified, and the data are shown in Figure Q15.13A. To examine the mechanism by which anti-platelet antibodies cause cell destruction, and the mechanism by which IVIG protects against the destructive effects of the anti-platelet antibodies, studies are performed in two lines of knockout mice. One line of mice is lacking expression of the FcRIII receptor, and the other line of mice is lacking expression of the FcRII receptor. The data from each of these studies is shown in Figure Q15.13B. Based on these data, FcRIII is most likely: #3

An activating Fc receptor that stimulates phagocytic uptake and NK cell killing

A mouse model for autoimmune hemolytic anemia can be transferred to naive mice by a single injection of anti-red blood cell IgG antibodies. However, the disease is prevented if recipient mice lack IgG-binding Fc receptors. These data indicate:

An essential role for NK cells, neutrophils and other granulocytes, and macrophages in red blood cell destruction

Based on these data, FcRII is most likely: #2

An inhibitory Fc receptor that inhibits macrophage phagocytic uptake via activating Fc receptors

Fatal anaphylaxis can be induced in mice by sensitizing the mice to penicillin V (Pen V). To elicit this response, Pen V is conjugated to a protein, such as chicken ovalbumin (OVA), and mice are immunized with this conjugate by intraperitoneal (IP) injection in a TH2-inducing adjuvant. Fourteen days later, mice are injected intravenously (IV) with Pen V conjugated to a different protein, bovine serum albumin (BSA), and examined 20 minutes later. In addition, a second set of mice received anti-IL-4 antibody injections on days 0, 2, and 4 of the sensitization phase of the response. The results in Table Q14.16A were observed; (data are shown as the ratio of dead mice to total mice for each condition): In the next experiment, mice were immunized by IP injection of Pen V-OVA, as above. Twenty-four days later, serum from these mice was isolated and injected into a set of naive (unimmunized) recipient mice. Recipient mice were then sensitized by a single IP injection of Pen V-OVA in adjuvant, as above, and then 24 hours later, were given an IV injection of Pen V-BSA or BSA alone. In addition, one group of mice received serum that was depleted of specific antibodies prior to transfer into recipients. These mice develop a slightly milder disease, characterized by severe shock rather than death. Data are shown in Table Q14.16B as the ratio of mice exhibiting severe shock to total mice for each condition/ Which antibodies were depleted from the serum in the final experiment shown above:

Antibodies to IL-4

Important information can be learned by studying the immune system of female carriers of the XLA disease gene. These individuals, identified as mothers of boys with XLA, show non-random X chromosome inactivation in their B cells, but random X chromosome inactivation in all of their other cells, including their T cells and macrophages. This finding indicates that:

B cells require the BTK protein for normal development.

A mutant mouse line (Mutant-X) is discovered that is defective in generating IgG or IgA antibody responses to immunization with the inactivated influenza A virus vaccine. As a first step in determining the gene responsible for the immunodeficiency, T lymphocytes and B lymphocytes are separately isolated from wild-type or Mutant-X mice and mixtures of cells are transferred into Rag-deficient recipients, which are then immunized with the Influenza A vaccine as shown in Figure Q13.10A. Fourteen days later, serum from the immunized mice is collected, and tested for anti-influenza IgG and IgA antibody titers. The results are shown in Figure Q13.10B: Given these data, the most likely identity for the gene that is defective in Mutant-X mice is:

CD40-ligand

Immune responses to tumors have been studied extensively in mice, using transplantable tumors injected into syngeneic mice. The basis for many of these studies is the assumption that the process of tumorigenesis generates mutations in genes encoding self-antigens that would allow the immune system to see these mutant proteins as 'foreign'. In this scenario, the dominant immune response targeting the tumor cells would be mediated by:

CD8 T cells

Cyclosporin A and rapamycin are each used as T cell immunosuppressants. They share the property of binding to immunophilin molecules in T cells as the initial step in their mechanisms of action. However, in the case of cyclosporin A, the drug:immunophilin complex binds to and inhibits the protein phosphatase calcineurin, whereas the rapamycin:immunophilin complex binds to and inhibitors mTOR. As a consequence,

Cyclosporin A, but not rapamycin, blocks cytokine production by T cells.

Patients with Wiskott-Aldrich syndrome show severely impaired responses to vaccines such as the tetanus vaccine, which is composed of the inactivated tetanus toxin (i.e., tetanus toxoid). Yet, these patients can generate normal antibody responses to bacterial polysaccharide antigens. This selective defect in antibody responses in Wiskott-Aldrich syndrome patients is due to:

Defective polarized secretion of cytokines by CD4 T cells

Multiple autoimmune diseases are associated with particular alleles of MHC class II molecules. For example, individuals expressing HLA-DR2 are nearly 16 times more likely to develop Goodpasture's syndrome than individuals expressing other HLA-DR alleles. The evidence to date indicate that these associations between MHC class II alleles and specific autoimmune diseases are due to:

Differences in the peptide-binding properties of different MHC class II alleles

HIV-infected patients that progress to AIDS suffer from a variety of opportunistic infections that rarely cause disease in healthy individuals. In addition, many of these patients acquire malignancies, such as B-cell lymphomas or Kaposi's sarcoma. A common feature of these two malignancies is that they are:

Each associated with a herpesvirus infection

Abatacept is a biologic drug that is a fusion protein formed from the B7-binding domain of CTLA-4 fused to the human IgG1 constant region. In patients suffering from rheumatoid arthritis (RA), high levels of granzyme B in the synovial fluid of inflamed joints is thought to contribute to joint erosion. When treated with abatacept, a subset of patients shows significant improvement in their RA symptoms together with decreased levels of granzyme B in their affected joints. These data indicate that the granzyme B found in RA patients' inflamed joints is predominantly made by:

Effector T cells

Herpesviruses are a class of viruses that establish life-long infections in human hosts. Estimates suggest that >90% of the population is infected with several of these viruses, including EBV, CMV, and herpes zoster, the cause of chicken pox. One herpesvirus, Herpes Simplex virus, causes recurrent cold sores in infected individuals. Thus, in spite of a robust anti-viral CD8 T cell response, these individuals still suffer from periodic virus-induced cold sores following exposure to UV light or certain hormones or other stressors. This anti-viral CD8 T cell response:

Eliminates infected epithelial cells but not infected neurons

Allergen-induced airway remodeling in mice is used as a model for human allergic asthma. This disease is induced by first sensitizing mice to the protein antigen, chicken ovalbumin (OVA) by intraperitoneal immunization with OVA in a TH2-inducing adjuvant. Three weeks later, mice are challenged by inhalation of aerosolized OVA (or saline alone, as a control) daily for the following three weeks. At the end of the entire six week period, the lungs of the mice are examined for leukocyte numbers in the bronchial alveolar lavage fluid (BALF) and for tissue remodeling as assessed by measuring fibrotic areas in the lung tissue. To determine the cell type most likely responsible for the tissue damage in this disease, IL-5 receptor-deficient mice (IL5R-/-) are compared to wild-type, as shown in Figure Q14.13. The cell type most likely responsible for the tissue damage in this allergen-induced airway remodeling disease model is:

Eosinophils

Immune privileged sites, such as the brain, the eye, and the testis, are often the targets of autoimmune attack. Thus, once effector T cells are generated that have specificity for autoantigens expressed in these tissues, the effector cells can gain entry to the tissue and cause tissue damage. However, under normal circumstances, the priming and differentiation of effector cells specific for antigens found in the brain, for example, is generally prevented. This is because 'immune privileged' sites:

Express the cytokine, TGF-beta

Studies have shown that secondary lymphoid tissues are a major reservoir of HIV in infected individuals. In part, this is due to the high numbers of viral target cells expressing CD4, such as T cells, macrophages, and dendritic cells. Surprisingly, secondary lymphoid tissues were also found to contain large numbers of infectious virus particles in the form of immune complexes. A comparison of the viral species found in these immune complexes indicates that they include virus particles that have been retained for over a year. The cells responsible for this reservoir of infectious HIV are:

Follicular dendritic cells

A common misconception is that our immune system fails to make a productive immune response to HIV infection, thereby leading to chronic infection. In fact, following a primary HIV infection, our immune system:

Generates a response that efficiently controls viral replication

HAART therapy is widely used in the US to treat HIV-infected individuals. This treatment is quite effective at inhibiting HIV replication, thereby preventing the progression to AIDS. However, HAART treatment is unable to completely eradicate all viral stores; consequently, patients must remain on this treatment indefinitely, as cessation of treatment leads to a rapid rebound in viral replication. One additional important side benefit of HAART treatment is its ability to:

Greatly reduce HIV transmission

The first drug treatment for HIV licensed in the US was zidovudine (AZT), a reverse transcriptase inhibitor. However, AZT has now been completely replaced by HAART as the recommended treatment for HIV-infected individuals. The use of HAART, rather than AZT, is preferred because:

HAART is a combination therapy that reduces the possibility of viral escape mutants.

In the late 1990s, a group of individuals was discovered that remained uninfected with HIV, in spite of multiple exposures to the virus. Analysis indicated that these HIV-resistant individuals had a homozygous deficiency caused by a 32-bp deletion in a single gene, and furthermore, that this mutation was present at a frequency of ~10% (in heterozygous form) in individuals of European descent. These data provided clear evidence indicating that:

HIV infection requires a co-receptor in addition to CD4.

In 1918, a worldwide epidemic of influenza A resulted in the deaths of 40-50 million people. This strain of influenza A, known as H1N1—referring to the genotypes of the viral surface proteins, hemagglutinin (H) and neuraminidase (N)—was shown to be derived from an avian virus that adapted to infect and grow in human cells. Interestingly, by 1957, the H1N1 strains of Influenza A had completely disappeared from the human population, to be replaced by new strains (H2N2) that contained three gene segments from avian origin. The most likely explanation for the disappearance of the early twentieth century form of H1N1 Influenza A virus is:

High levels of existing immunity in the human population to the H1N1 surface antigens

Once an individual becomes sensitized to an allergen, such as an inhaled antigen, the allergic response can become self-amplifying upon each re-exposure to the allergen. Thus, even in the absence of CD4 TH2 cell activation, increases in IgE secretion by mucosal-resident plasma cells can be induced by:

IL-4 secretion and CD40-ligand expression by mast cells and basophils

Studies using mouse models of allergic asthma have provided information about the cell types and soluble mediators that contribute to this disease. One common experimental model uses airway exposure to protease allergens, such as papain from papaya or the house dust mite allergen. Interestingly, papain is able to induce allergic lung inflammation even in RAG-deficient mice. In this system, the type 2 cytokines, IL-5, IL-9, and IL-13, are likely coming from:

ILC2 cells

On occasion, individuals on antibiotics such as Minomycin have an allergic response to the antibiotic. Symptoms often include an urticarial rash on the skin, and swelling (edema) of the legs and ankles. When this occurs, patients are advised to stop taking the antibiotic, and are treated with corticosteroids. During follow-up visits to their physician, patients are often given a skin test for hypersensitivity to the drug. This skin test involves intradermal injection of a small amount of Minomycin, and 15 minutes later the site of injection is examined for redness and swelling. In cases where this skin test is negative, the patient most likely generated:

IgG antibodies to the Minomycin

A small subset of patients taking antibiotics such as minocycline develop symptoms resembling those of systemic lupus erythematosis (SLE). These symptoms include a severe skin rash that may cover the legs and trunk, arthritic joint pain, and swelling of the lower limbs, as well as the face, lips, ears, and tongue. These symptoms subside once the antibiotic is discontinued. In these individuals, a skin test for hypersensitivity to minocycline within 15 minutes of intradermal injection of the drug is negative. Analysis of the peripheral blood from these patients would likely reveal:

IgG antibodies to the minocycline antibiotic

Currently, the only licensed vaccine against Mycobacterium tuberculosis (Mtb) is the attenuated strain, related to Mtb, known as BCG. While BCG protects some populations against some strains of Mtb, an improved vaccine for this deadly disease is needed. One recent effort to generate a better vaccine against Mtb is to engineer BCG to have improved immunogenicity in vaccinated individuals. BCG, like Mtb, infects macrophages, replicating in the macrophage phagosomes. Both BCG and Mtb prevent phagosome acidification and fusion with lysozomes, thereby preventing macrophages from efficiently killing the ingested bacteria. In addition, antigens from the bacteria are not found in the macrophage cytosol. To alter this lifestyle, BCG was engineered to express the listeriolysin protein from Listeria monocytogenes. This enzyme lyses the phagosomal membrane allowing antigens to escape into the cytosol. In addition, a mutation was generated in this same BCG to inactivate the bacterial urease, an enzyme that prevents acidification of phagosomes carrying ingested bacteria. This modified BCG was called rBCG, for recombinant BCG. To test whether rBCG induced more potent protection than the original vaccine strain, mice were immunized with BCG or rBCG, or left unimmunized, and then challenged with virulent Mtb. Titers of Mtb (CFU/lung) were then examined over time after challenge, as shown in Figure Q16.25. Based on these data, rBCG likely induced:

Increased cytolytic CD8 T cells capable of killing Mtb-infected macrophages

NRF2 is a transcription factor that is required to induce anti-oxidant genes, such as glutathione-S-transferase genes, in response to reactive oxygen and reactive nitrogen species released by inflammatory cells in the airways following phagocytosis of inhaled particles. Mice deficient in Nrf2 were tested for their allergic airway response to inhaled allergens in comparison to wild-type controls. Compared to wild type mice, the Nrf2-/- mice would be expected to show:

Increased levels of IL-4 and IL-13 in the airway

A small group of HIV-infected individuals are known as 'elite controllers.' These individuals have HIV viral RNA copy numbers that persistently remain <50 copies/ml of plasma. Studies examining the immune response to the virus in these individuals would likely reveal:

Increased numbers of virus-specific CD4 and CD8 T cells secreting IFN- compared to individuals with high viral titers

Yersinia pestis, the causative agent of the bubonic plague, has multiple mechanisms of immune evasion. This Gram-negative bacterium is transmitted from fleas (body temperature, 26°C) to humans (body temperature, 37°C) by flea bites. Studies have shown that the lipopolysaccharide (LPS) produced by Y. pestis grown at 37°C is about 10-fold less potent at stimulating TLR4 signaling than is the Y. pestis LPS from bacteria grown at 26°C. When these two forms of Y. pestis LPS are compared for their abilities to induce responses from human macrophages, one would expect that the 26°C Y. pestis LPS would result in:

Increased production of TNF- and IL-6

The 'hygiene hypothesis' has been proposed as an explanation for the rapid increase in allergies and asthma incidence in Western countries over the last half century. One line of evidence supporting this hypothesis is:

Individuals of African descent have much higher incidence of atopic disease when living in Western countries.

HIV encodes several proteins that function to promote viral replication, packaging, and budding from host CD4 T cells. In addition to inhibiting cell-intrinsic antiviral mechanisms and down-regulating surface expression of MHC class I and class II molecules, these proteins function to:

Induce robust, sustained CD4 T cell activation

Allergic responses to inhaled antigens occur when an individual is first sensitized to the antigen (i.e., the allergen), inducing an immune response, and then has a subsequent exposure to the same antigen. The sensitization phase is characterized by:

Induction of a CD4 T cell type II immune response

One important feature of retroviruses such as HIV is their generation of a provirus, a copy of the viral genome that is inserted into the host cell chromosome. In addition to providing a template for viral mRNA transcription, the proviral genome:

Is maintained long-term and transmitted to all of the cell's progeny

A mouse model for multiple sclerosis is induced by immunizing mice with murine central nervous system proteins mixed with Complete Freund's adjuvant. This adjuvant contains components that stimulate both TLR2 and TLR4. The adjuvant is essential to the development of autoimmunity because:

It activates dendritic cells to up-regulate co-stimulatory molecules.

One of the first biologics developed was a drug known as etanercept (common name, Enbrel) that is a fusion protein formed from the cytokine binding domain of the TNF-receptor fused to the human IgG1 constant region, as shown in Figure Q16.6. This biologic is used to treat patients with inflammatory diseases such as rheumatoid arthritis, psoriasis, and others. Etanercept was developed to avoid injecting patients with the mouse monoclonal antibody to TNF-, which was available at the time. Etanercept was preferred because:

It would not elicit an anti-drug antibody response

The first JAK kinase inhibitor to be developed, tofacitinib, inhibits JAK1 and JAK3. These two JAK kinases are required for the signaling pathways induced by multiple cytokines, including all of the receptors that share the cytokine receptor common gamma chain (c; includes the receptors for IL-2, IL-4, IL-7, IL-9, IL-15, and IL-21), all of the receptors that share gp130 (includes the receptor for IL-6), the receptors for GM-CSF, IL-12, and IL-23, and both type I and type II (i.e., IFN-) interferon receptors. Tofacitinib has recently been shown to be effective in the treatment of severe rheumatoid arthritis, an autoimmune disease characterized by inflammation of the joints with prominent inflammatory cell infiltrates, autoantibodies, and eventual cartilage and bone destruction. A likely explanation for the therapeutic benefits of tofacitinib in this disease is:

Its ability to block innate as well as adaptive immune responses

Listeria monocytogenes is a bacterial pathogen that causes a variety of diseases including gastroenteritis, encephalitis, and sepsis. The bacterium has evolved a strategy to replicate in the cytosol of macrophages, and to spread from one macrophage to another using the host's actin machinery to facilitate direct transfer between cells, thereby avoiding the extracellular space. This unique lifestyle of L. monocytogenes is dependent on the bacteria encoding enzymes that:

Lyse the phagocytic vesicle membrane, allowing bacterial escape into the cytoplasm

Genetic linkage studies have identified numerous genes in which certain polymorphisms are associated with a predisposition to autoimmune disease. Yet in most cases, the effects of individual genetic polymorphisms are very small, with each one being linked to a very modest effect on disease incidence. This indicates that:

Many different environmental factors are determining which predisposed individuals develop autoimmunity.

Celiac disease occurs when an individual makes an aberrant immune response to a protein in gluten, such as -gliadin. Evidence suggests that very few proteins are able to elicit the immune response that causes celiac disease. A key piece of this evidence is that:

More than 95% of patients express the MHC class II DQ2 allele.

Individuals that lack all T cells have the most severe form of immunodeficiency (SCID) and will not survive past their first birthday without a bone marrow transplant from a healthy donor. These individuals fail to make antibody responses to the normal childhood vaccines because:

Most antibody responses require T cell help for the B cells

In individuals with a peanut allergy, mild allergic responses are those that involve a single site, typically a skin reaction such as hives. More severe allergic reactions generally involve multiple tissue sites, such as the skin, oral mucosa, airway mucosa and gastrointestinal tract. Given two groups of allergic patients, one with only skin responses, and the other with 3-4 different tissue sites involved, one would expect that:

Patients with the severe allergic responses would have higher concentrations of allergen-specific IgE.

Red blood cells are common targets of drug-induced anemia, a disorder that occurs when some drugs bind to the surface of red blood cells and trigger the development of IgG antibodies that bind to the drug-coated red blood cell and promote red blood cell destruction. Since the drug binding to the red blood cell surface does not actually harm the red blood cell, the anemia resulting in this disorder is caused by:

Phagocytosis by Fc-receptor expressing macrophages in the spleen

In 2015, the US FDA approved the use of secukinumab for the treatment of psoriasis, a disease caused by chronic inflammation in the skin. Secukinumab is fully human monoclonal antibody against IL-17A. Clinical trials of this treatment indicated an increased rate of infections in patients on secukinumab, the majority of which were upper respiratory tract infections caused by viral or bacterial pathogens. For many of these infections, this side effect of secukinumab can be explained by:

Poor recruitment of neutrophils to infected airways

Due to its multiple roles in promoting inflammatory responses, the complement system has been a target for the development of compounds that interfere with the complement system as a means of treating chronic autoimmune diseases. While some compounds inhibit the formation of the membrane attack complex, others are aimed at inhibiting earlier steps in the complement cascade. One such compound is an inhibitor of the C5a receptor, a receptor expressed on macrophages, dendritic cells, and granulocytes. The C5a receptor inhibitor would function to:

Prevent the recruitment of macrophages and neutrophils to the sites of autoantibody binding

A disease resembling systemic lupus erythematosis (SLE) can be induced in mice. A key characteristic of this disease is the production of autoantibodies with specificity for double-stranded DNA (dsDNA), nucleosomes, and ribonucleotide-protein complexes (RNPs). When these mice are treated with a small molecule TLR7 and TLR9 inhibitor, twice a week starting at 4 months of age, the data in Figure Q15.4 are obtained. In this system, the TLR7/TLR9 inhibitor:

Prevents B cell activation due to uptake of chromatin from apoptotic host cells

Immunotherapies aimed at promoting anti-tumor immune responses are being developed for tumors of many different tissue or cell-type origins. Interestingly, some of these approaches, when tested in clinical trials, were found to also cause patients to develop autoimmune symptoms related to their tumor type. For instance, in patients with malignant skin cancer (melanoma), immunotherapy treatment can develop an autoimmune disorder known as vitiligo, in which T cells attack and destroy melanocytes in the skin, causing depigmentation. These findings indicate that, in some individuals the melanoma-specific anti-tumor T cell responses are directed at:

Proteins normally expressed in melanocytes

The vitamin D3 metabolite 1,25(OH)2D3 binds to the vitamin D receptor (VDR). This complex then functions as a transcriptional regulator. The activation of VDR following treatment of cells with 1,25(OH)2D3 has been found to modulate the activity of antigen-presenting dendritic cells. In one study, dendritic cells were isolated from wild-type mice and activated in vitro by stimulation with LPS plus IFN- in the presence or absence of 1,25(OH)2D3 for 24 hours. These activated dendritic cells were then pulsed with a peptide from the chicken ovalbumin protein (OVA) that binds to MHC class II and is recognized by OT-II CD4 T cells. The peptide-pulsed dendritic cells and T cells were incubated together for 3 days, and then IL-2 levels in the supernatants were measured, as shown in Figure Q6.12. Based on these data, dendritic cells activated in the presence of 1,25(OH)2D3 are likely to show:

Reduced MHC class II and reduced B7 expression compared to controls

In the late 1990s, compounds that functioned as leukotriene receptor antagonists were approved for the treatment of asthma. The first such drug, zafirlukast, inhibits the actions of a major receptor for leukotrienes, known as CYSLTR1 (cysteinyl leukotriene receptor 1). One would predict that patients on this drug would show:

Reduced bronchoconstriction

A relatively new form of therapy for IgE-mediated allergic diseases is the periodic injection of patients with anti-IgE antibody. This antibody binds to the Fc portion of IgE antibodies, and prevents the IgE antibodies from binding to both high affinity and low affinity IgE receptors on inflammatory cells. IgE bound to the high affinity IgE receptor on mast cells and basophils stimulates degranulation of these cells and their production of inflammatory mediators, following antigen encounter. In contrast, the low affinity IgE receptor is expressed on dendritic cells, and functions to trap allergen-IgE complexes for uptake, degradation, and presentation to T cells. Given these functions, individuals treated with this anti-IgE therapy would be expected to show:

Reduced symptoms upon allergen encounter and no progressive worsening of disease

Genetic variations in proteins involved in immune and inflammatory responses have been shown to be associated with the development of atopic dermatitis and other allergic diseases. However, several genes associated with these conditions do not affect the immune system directly. For example, among this latter group are genes that:

Regulate barrier function by airway and skin epithelial cells

Polymorphisms in the IL-2R chain gene are associated with multiple autoimmune diseases, including type 1 diabetes, vitiligo, multiple sclerosis, Crohn's disease, autoimmune thyroiditis, and juvenile arthritis. One hypothesis for this striking list of disease associations with polymorphisms in the IL-2R chain gene is that these alterations affect the function of FoxP3+ regulatory CD4 T cells. If this was the case, one would expect that disease-associated alleles of the IL-2R chain gene would:

Result in reduced responsiveness of FoxP3+ regulatory CD4 T cells to IL-2

A mouse model for type 1 diabetes, the NOD mouse, has a well-described sex bias in the incidence and rate of diabetes onset. Female NOD mice are about twofold more likely to become diabetic, and do so on average about six-weeks earlier than male NOD mice. Recent studies have shown that a large component of this sex bias is due to differences in the intestinal microbiota between male and female NOD mice. In fact, colonization of young female NOD mice with male microbiota reduced the incidence and time to onset of diabetes in the transplanted mice, resulting in a disease course resembling that of the typical male NOD mice. These data indicate that:

Sex-based differences in microbiota have a substantial impact on immune system regulation.

Bone marrow transplantation is currently used to treat many immunodeficiency diseases resulting from defects in hematopoietic cells, such as lymphocytes or myeloid cells. Often, the donor of the bone marrow is a healthy relative of the patient, such as a sibling or a parent (Table Q13.18). Which of the individual relatives above would not be a potential donor for the patient's bone marrow transplant?

Sibling 1

One group of immune deficiency diseases is caused by an inability of CD8 effector T cells to kill virus-infected target cells, due to defects in cytotoxic vesicle exocytosis. Because of the inflammatory response that accompanies a normal virus infection, together with the prolongation of this response due to the inability to control the infection, patients with these disorders suffer from tissue damage caused by the infiltration of effector CD8 cells and activated macrophages into multiple organs. In addition, a subset of these patients also show increased susceptibility to extracellular and intracellular bacterial infections. This is because:

Some proteins required for cytotoxic vesicle exocytosis are required for phagosome-lysosome fusion.

The response of most individuals to contact with poison ivy includes the development of redness, swelling, blistering (edema fluid accumulation between the dermis and the epidermis), and itching. If one intended to transfer this response from a sensitized to a naive individual, one would transfer:

T cells from the skin-draining lymph nodes of the sensitized to the naive individual

In the first few days following organ transplantation, patients are often treated with several doses of an antibody mixture known as anti-thymocyte globulin. The anti-thymocyte globulin is generated by immunizing rabbits or horses with human T cells, to generate antibodies against the human T cell surface molecules. Following the anti-thymocyte globulin treatment, patients are generally put on a sustained regimen of cyclosporin A or other small-molecule immunosuppressive drugs. The immediate post-operative treatment with anti-thymocyte globulin is likely used to:

Temporarily deplete the patient's T cells

All-trans retinoic acid (tRA) is a metabolite generated from vitamin A in the diet, and is a key component in generating an appropriate balance of FoxP3+ regulatory CD4 T cells versus TH17 effector CD4 T cells in mucosal tissues. Patients with some autoimmune diseases, such as psoriasis, derive benefit from oral synthetic retinoid treatment for their condition. This indicates:

That environmental factors such as diet can impact the onset of autoimmunity

An area of cancer immunotherapy that is undergoing rapid development is the use of agents that function as checkpoint blockaders. These agents work by interfering with receptors on T cells that normally induce inhibitory signals that suppress T cell responses. For example, one clinical trial tested the effects of a drug known as ipilimumab, which is a human monoclonal antibody that binds to and inhibits CTLA-4, on patients with metastatic melanoma, a deadly form of skin cancer. A simplified version of these data are shown in Figure Q16.20. In this case, one group of patients received a peptide vaccine, comprised of a mixture of HLA class I-binding peptides derived from the melanoma antigen, gp100. A second group of patients received ipilimumab, and a third group received the gp100 peptide vaccine + ipilimumab. While mean survival times between the treatments were not that remarkable (~10 months for the two groups receiving ipilimumab versus ~6 months for the gp100 peptide vaccine alone), the remarkable finding was the durable long-term survival of ~20% of the patients receiving ipilimumab. However, based on the similarity in the data for the group of patients receiving ipilimumab plus the gp100 peptide vaccine versus those receiving ipilimumab alone, the most likely affect of the ipilimumab is:

That it allows T cells already present in the patient to kill tumor cells more effectively

CAR T cells have shown remarkable efficacy in treating hematological malignancies (e.g., leukemias). More recently efforts have been underway to design CAR T cells to target solid tumors. One example currently in trials is a CAR T cell therapy for tumors expressing the protein mesothelin, a tumor associated-antigen found on many pancreatic cancers, ovarian cancers, and some lung cancers. A design of a CAR to target mesothelin is shown in Figure Q16.17. In this cartoon, the component of the CAR indicated by the arrow is composed of:

The Fab fragment of an anti-mesothelin antibody

Some early studies aimed at deciphering the mechanisms involved in immunological tolerance, and its breakdown in cases of autoimmune disease, were based on generating transgenic mice that constitutively expressed a viral protein in the -islet cells of the pancreas. These mice were crossed to transgenic mice expressing a T-cell receptor specific for MHC class I bound to a peptide of this viral protein. The double transgenic mice generated large numbers of CD8 T cells capable of recognizing this viral antigen on -islet cells, yet the mice never spontaneously developed type I diabetes, a disease in which -islet cells are destroyed by T cells. This lack of response most likely reflects:

The absence of infection or tissue damage needed to trigger the priming of effector T cell responses

Some forms of SCID are due to defects in common 'housekeeping' enzymes, such as enzymes involved in nucleotide biosynthesis pathways, that are present in all cells of the body. These genetic deficiencies cause SCID because:

The absence of these enzymes causes build-up of intermediates in the pathway that are toxic to developing lymphocytes.

Systemic lupus erythematosis (SLE) is an autoimmune disease characterized by the development of autoantibodies specific for DNA and other nuclear antigens. Patients with SLE show a wide variety of symptoms that include anemia, skin rashes, joint and muscle pain, heart problems, and kidney damage. This is considered a systemic autoimmune disease because:

The autoantigen targeted by the immune system is not-tissue specific.

Unlike defects in antibodies or T cell functions, defects in complement components often lead to autoimmune-like symptoms, rather than to increased susceptibility to infections. This is because:

The complement pathway normally functions to clear immune complexes from the circulation.

Infants with RS-SCID short answer

The defect is in the DNA repair system. The high degree of cancer is still there.

A subset of patients with imbalances in glucose metabolism are found to have autoantibodies to the insulin receptor. These patients, as well as patients with myasthenia gravis, may be treated with a procedure known as plasmapheresis. During plasmapheresis for these disorders, blood is removed from the patient, and then separated into two fractions, one containing cells, and the other containing the plasma. The plasma is then treated to deplete it of antibodies, and then the cells plus the antibody-depleted plasma are returned to the patient. This cumbersome treatment may be necessary because, for these diseases:

The disease symptoms are a direct effect of autoantibody binding to its target receptor cells

Individuals with defects in ubiquitously expressed DNA repair proteins have a form of SCID known as RS-SCID (radiation-sensitive SCID). Studies have shown that, in addition to immune deficiencies, these patients have an increased rate of cancer. Yet, in general, they are diagnosed first based on their immunodeficiency disease, not on their susceptibility to getting cancer. This is due to the fact that:

The immune response to infections is required almost immediately after birth.

Individuals with a complete absence of B cells and antibodies, such as patients with XLA, show a limited range of susceptibilities to infection rather than a global immunodeficiency to all categories of pathogens. For example, XLA patients show increased susceptibility to pyogenic bacterial infections, as antibody binding to these microbes is critical for their uptake and destruction by phagocytes. Clinicians caring for these patients are advised regarding their vaccinations, some of which could be highly dangerous to the antibody-deficient patient. In particular, XLA patients should never receive:

The live oral polio vaccine, composed of an attenuated strain of the enteric poliovirus

Large clinical trials have been performed to compare the vaccine efficacy of the live-attenuated influenza virus vaccine with that of the inactivated virus vaccine. In all, data from over 25,000 children aged 6-71 months were analyzed. The conclusion was that the children who received the live-attenuated vaccine reported 50% fewer cases of influenza than those who received the inactivated vaccine. One difference in the immune response elicited by the live-attenuated versus the inactivated vaccine is:

The live-attenuated vaccine elicits antiviral CD8 effector responses but the inactivated vaccine does not.

Individuals with peanut allergies can exhibit a variety of symptoms following exposure to the peanut allergen. These symptoms can include a runny nose, skin reactions such as hives, itching in the mouth and throat, digestive problems such as cramps, diarrhea or vomiting, and shortness of breath or wheezing. This variety of symptoms is a result of:

The presence of mast cells with pre-bound IgE in all mucosal tissues

Mycophenolate mofetil is a cytotoxic drug that is commonly used in patients receiving kidney transplants, as part of a combination therapy with other immunosuppressive drugs. Studies have been performed to assess whether reductions in mycophenolate mofetil dose given to transplant patients starting around 4 months post-transplant have deleterious effects on the transplanted kidney function or on episodes of graft rejection. The motivation for this type of study is:

The side effects of the cytotoxic drug on healthy dividing cells in the body

In some cases, a transient autoimmune process can occur as a result of an infection. This may be due to molecular mimicry between the pathogen and a self-antigen, or to the release of normally sequestered self-antigens due to tissue damage from the infection. An important factor leading to these autoreactive immune responses is the activation of dendritic cells by the infection-induced inflammation. Once the infection is resolved, this inflammation will also subside. As a consequence, autoreactive T cells may no longer receive sufficient signals to promote their activation, causing a remission in the autoimmune symptoms. One important change in antigen-presenting dendritic cells during an infection that would contribute to the activation of normally self-tolerant self-reactive T cells is:

The up-regulation of MHC class I and class II molecules on activated dendritic cells

In the case of HIV infection by sexual transmission, a key step in the establishment of disseminated HIV infection is the replication of the virus in regional lymph nodes draining the mucosal site of initial virus entry. The ability of the virus to spread from the mucosa to the regional lymph node is made possible by:

The virus' ability to infect migratory cells that carry it from the mucosa to the lymph node

In mice, an allergic response in the airways can be induced by systemic immunization with a protein antigen (chicken ovalbumin) in an adjuvant that promotes Type II immune responses, followed by several exposures to aerosolized ovalbumin administered via the airways. Mice that have a genetic deficiency in expression of the receptor c-kit are resistant to this disease because:

They lack mast cells.

Defects in components of the complement pathway do not lead to recurrent or persistent virus infections.

True

The US Department of Health and Human Services has a stated goal for the seasonal influenza vaccine of vaccinating 80% of healthy (i.e., low-risk) individuals. This vaccine is formulated each year from the serotypes of influenza likely to be circulating in the population during the coming flu season. The reason this goal is not 100% of individuals is because:

Unvaccinated individuals are protected when 80% of people around them are vaccinated.

Immunotoxin therapy as an anticancer treatment is a focus of current efforts to develop new anticancer drugs. An alternative strategy, known as radioimmunotherapy, involves the conjugation of a tumor-antigen specific antibody to a radioisotope, rather than to a bacterial toxin. One advantage of radioimmunotherapy over that of immunotoxin therapy is that the radioisotope:

Will damage neighboring tumor cells in addition to the cell binding the drug

Treg cells that express FoxP3 are generally thought to have T-cell receptors that recognize self-peptides bound to MHC class II molecules. In the skin, keratin and filaggrin are among the self-antigens expressed. FoxP3+ Treg cells found in skin and skin-draining lymph nodes might be specific for the self-antigen, filaggrin. These FoxP3+ filaggrin-specific Treg cells:

Would inhibit the activation of naive filaggrin-specific and keratin-specific CD4 T cells

Patients with X-linked lymphoproliferative syndrome type 1 (XLP1) have mutations in the SLAM-family adapter protein, SAP. These patients suffer from an inability to control infections of the herpesvirus Epstein-Barr virus (EBV) that infects B cells. Studies have been done using peripheral blood T cells from these patients to examine their response to EBV in comparison to the responses of normal individuals (EBV-infected) as controls. These data were obtained by ELISPOT analysis, to quantify the numbers of IFN--producing CD8 T cells per million peripheral blood leukocytes in response to several EBV peptides, indicated as peptide 1, 2, 3, or 4 (note: the patients and controls were matched for HLA class I molecules; Figure Q13.13).

XLP patients have normal CD8 effector cell priming following EBV infection.

A variety of genetic defects can result in patients exhibiting SCID. For many of these diseases, infants with the disease are given bone marrow transplants from healthy donors to restore normal immune function. Yet, some diseases causing T cell deficiencies cannot be treated by bone marrow transplantation. Which of the diseases below is treatable by giving patients hematopoietic stem cells from a healthy donor?

XSCID

Common allergens that trigger atopic responses in humans share several features. For example, nearly all allergens are proteases.

false

Hypersensitivity responses to divalent cations such as nickel are relatively common. Individuals sensitized to these metals will develop a skin rash within 15 minutes of putting on a bracelet or ring containing that metal.

false

Multiple mechanisms provide a series of checkpoints that function to maintain immunological self-tolerance. A breakdown in any one of these mechanisms is likely to lead to autoimmunity.

false

The majority of monogenic defects in humans that cause autoimmune diseases are in genes that regulate T cell responses. These include the AIRE, CTLA4, FOXP3, and FAS genes. These findings indicate that B cells and innate immune cells are not important in autoimmunity.

false

The prevention of inflammatory immune responses to inhaled antigens in healthy individuals has mechanisms in common with those that prevent inflammatory immune responses to commensal microbes in the gut. One important component of immune regulation shared by these two situations is:

he important role for CD4 regulatory T cells in suppressing inflammatory immune responses in these tissues

A recent strategy showing some promise for the treatment of IgE-mediated allergies is a form of allergen immunotherapy, in which allergic individuals are given 3-4 intradermal injections of soluble peptides. For example, in one study, allergic individuals were injected with a set of 13-17 amino acid long peptides derived from the house dust mite protein antigen; these peptides were selected based on predictions for sequences likely to be MHC class II binding epitopes. Following the treatment, individuals were found to have increased numbers of antigen-specific IL-10-producing CD4 T cells, a finding that correlated with reduced allergic responses to allergen challenge. One of the goals of this therapy might also be to:

induce apoptosis of allergen-specific effector CD4 T cells

Within minutes after encounter with an allergen, individuals with allergic rhinitis show symptoms of nasal itching, nasal congestion, sneezing, and a runny nose. These symptoms generally subside within 30 minutes, but reappear several hours later. Analysis of the nasal epithelium in such an individual 6 hours after allergen encounter would show:

infiltration of eosinophils, basophils, neutrophils, T cells, and macrophages

Studies performed in mice have revealed one important component affecting the altered immune response in individuals undergoing malnutrition or starvation. In these studies, mice were placed on a starvation diet for several days, and then immunized with a protein antigen in an adjuvant. One group of starved mice were given injections of 'compound X' for 48 hours, starting at the time of immunization. Seven days later, draining lymph nodes were isolated, and T cell responses were measured in vitro following stimulation with antigen. The results are shown in Figure Q13.19.

leptin

A mouse model of an immunodeficiency disease affecting the innate immune response was generated by knocking out a single gene. Studies of these mice, performed in the 1990s, showed that they were highly susceptible to infections of pyogenic bacteria, such as Staphylococcus and Lactobacillus species, and to infections of fungal pathogens, such as Paecilomyces. In fact, without deliberately infecting the mice, the researchers performing these studies found that the knockout mice were spontaneously succumbing to these infections while housed in their vivarium (animal facility), as shown in Figure Q13.16A. To determine the potential mechanism leading to the immune deficiency, a series of additional studies were performed. In one study, peripheral blood leukocytes from the mice were mixed with Staphylococcus aureus bacteria, and the ability of the cells to kill the bacteria was assessed. In a second study, the compound thioglycolate was injected into the peritoneal cavity of the mice, and five hours later the numbers of white blood cells were measured. This compound elicits a robust inflammatory response in the peritoneum, including the production of several inflammatory cytokines, such as TNF, IL-1, and IL-6, as well as a number of chemokines known to recruit neutrophils and monocytes from the blood to the site of inflammation. The results of these studies are shown in Figure Q13.16B.

p47, a component of NADPH oxidase

Antiretroviral drugs are effective at blocking HIV replication in infected individuals, and in reducing the rate of HIV transmission. Physical barriers to transmission have also been shown to be effective at blocking HIV transmission. An additional strategy for reducing the rate of new HIV infections in high-risk populations utilizes a strategy to prevent the virus from establishing a permanent infection, once an individual has been exposed. This strategy utilizes:

pre-exposure prophylactic treatment

All autoreactive CD4 T cells are not necessarily able to cause autoimmune diseases. Depending on the target tissue expressing the antigen recognized by the effector CD4 T cells, and the cytokines made by these effector T cells, autoimmune tissue damage may or may not occur.

true

Epidemiological evidence has indicated that exposure to particular infections can predispose individuals to specific autoimmune diseases. An example is the data linking Coxsackie virus infections with subsequent development of type 1 diabetes. In many cases, there is no indication of cross-reactive antigens between the pathogen and the autoantigens targeted by the autoimmune disease.

true

Evidence indicates that HIV-1 and HIV-2 originated in non-human primates, and only made the jump to infecting humans in the early twentieth century. As a consequence, these viruses are not well adapted to co-exist in equilibrium with their human hosts.

true