Chapter 23.

List the protective compounds of the lungs.

-Alveolar macrophages. -Cystic fibrosis transmembrane conductance regulator. -Mucociliary escalator. -Alveolar macrophages phagocytose most microbes in the lungs. The cystic fibrosis transmembrane conductance regulator (CFTR) is a membrane chloride channel that prevents infections in the lungs. CFTR hydrates mucus in the respiratory tract. This mucus traps microbes, which are then lifted out of the respiratory tract by the mucociliary escalator.

List the protective compounds of the skin.

-Langerhans cells. -Sebum. -Langerhans cells are phagocytic, antigen-presenting cells in the skin. Sebum is an oily substance that protects the skin.

Which complement pathway is activated by lipopolysaccharide?

Alternative complement pathway. -The alternative complement pathway is activated nonspecifically when complement protein C3b binds to lipopolysaccharide on the surface of Gram-negative bacteria. The lectin pathway is also activated nonspecifically by macrophage cytokines. The classical component pathway is activated by antibodies and so is a part of the adaptive immunity. There is no opsonin pathway.

List the description of Neutrophils (a polymorphonuclear leukocyte, or PMN).

Are phagocytic. Produce lattice-works of DNA that trap pathogens. Are the majority of leukocytes in blood.

Which is not an innate chemical defense used by the host to protect itself against infection? Which ones are?

Are: acidic pH, alpha defensins, lysozyme Not: microbe-associated molecular patterns. -Microbe-associate molecular patterns are produced by the invading microbe, not the host, and alert the host's immune system. They are not a part of the host's innate chemical defenses. They bind to Toll-like receptors and CD14 receptors on host cells and trigger the activation of the immune system.

An individual is infected with Mycobacterium tuberculosis. The bacteria infect macrophages in the lungs, where it survives and reproduces intracellularly. What is the most likely mechanism the infected macrophages will use to combat the invading bacteria?

Autophagy. -Autophagy is a mechanism used by cells to clear intracellular pathogens. In autophagy, the intracellular microbe is surrounded by double membranes, forming an autophagosome. Lysosomes fuse with the autophagosome, destroying the microbe. Autophagy is also used by the cell to remove damaged organelles.

The microbiome has both associated benefits and risks. What are some of the risks associated with the oral microbiome?

Bacteremia, Tooth decay, Subacute bacterial endocarditis. -Oral microbes cause tooth decay when they adhere to tooth enamel and produce acids through fermentation of sugars. The acids dissolve the tooth enamel. during dental procedures, oral microbes can enter the bloodstream and cause bacteremia. From the blood, microbes can then collect in imperfections in defective heart valves, causing subacute bacterial endocarditis. Oral microbes do NOT survive in the acid of the stomach and do NOT enter the genitourinary tract.

Michael has Acquired Immunodeficiency Syndrome (AIDS) caused by the Human Immunodeficiency Virus (HIV). The damage that the virus has done too Michael's immune system has made him susceptible to a yeast infection of his respiratory tract, called Candidiasis. Individuals with a healthy immune system do not develop this yeast infection. Michael is a(n) ________ and the yeast that causes Candidiasis is a(n) _______.

Because the HIV infection has compromised Michael's ability to fight infection, he is a compromised host. Yeast is an opportunistic pathogen in this case. Yeasts can be normal biota and usually do not cause respiratory infections unless the host's immune defenses are compromised.

In which body site would the mere presence of microbes indicate an infection?

Blood. -Blood does not have a normal microbiota and is sterile in healthy conditions. The presence of microbes in the blood would indicated and infection. An infection of the blood is called septicemia. The skin, bladder, stomach, and lungs all have normal microbiota. Microbes are present in these body sites in a healthy individual.

Which location is LEAST likely to harbor commensal microbes?

Blood. -Blood is usually sterile. The skin, mouth, and vagina interface with the external environment and are colonized by bacteria.

List the description of Basophils (a polymorphonuclear leukocyte, or PMN).

Contain IgE receptors associated with allergies. Are similar to mast cells.

Which chemical defenses are produced by host cells to destroy invaders' membranes?

Defensins. -The skin, stomach, and vagina are all somewhat acidic to inhibit bacterial growth. Superoxide radicals cause damage to the cell through their reactivity. Lysozyme degrades peptidoglycan. Defensins get drawn into the membrane by its electrochemical potential and form channels destroying the membrane.

Some cells of the innate immune system present antigens to T cells of the adaptive immune system. Cells that can present the antigens are logically called antigen-presenting cells (APCs) and include which of the following?

Dendritic cells. Macrophages. -Macrophages and dendritic cells present the antigens of pathogens that they have ingested and degraded to T cells. Thus, macrophages and dendritic cells are antigen-presenting cells. Neutrophils can also ingest and degrade pathogens through phagocytosis, but neutrophils do not present the pathogens' antigens to T cells.

Which cells are most likely to be killed via the alternative complement pathway?

Gram-negative bacterium. -The alternative complement pathway depends on C3b meeting LPS on an invading Gram-negative microbe. Virally infected host cells lack the LPS trigger and rely on antibodies, and hence the classical complement cascade. Gram-positive bacteria have a thick peptidoglycan layer that hinders access of complement components.

Type I interferons...

Help protect cells from viral infection. -Interferons are species-specific antiviral compounds. Among their activities, they increase levels of dsRNA endonucleases.

Microbes that colonize the skin need to be resistant to ________ salt and ______ pH.

High; Low. -The skin has a pH of 4-6 and relatively high salt concentrations due to epidermal secretions.

Organs have varied mechanisms for limiting the amount and types of colonizing microbiota. In the choices below, organs are matched with one of their microbiota-limiting mechanisms. Match the organs with their mechanisms. I. Lungs II. Eye III Intestine IV. Skin

I. Action of the mucociliary escalator. II. Constant washing action with antimicrobial factors such as lysozyme. III. Secretion of lectins that separate the microbiome from the host mucosal cells. IV. Presence of dry, high-salt environments.

Which are true regarding the immune system?

I. It is capable of responding to almost any foreign molecule. II. Its cells differentiate between self and non self. III. It includes organs, cells, and cell products. -Innate and adaptive immunity are not isolated from each other; they are interconnected. Innate mechanisms such as phagocytosis and antigen presentation can trigger the adaptive response. Likewise, adaptive antibodies can activate parts of the innate immunity.

List the four basic steps of the inflammatory response that occur after an infection. (Phagocytosis)

I. Macrophages engulf microbes and release cytokines. II. Movement of neutrophils through the capillaries slows and the junctions between endothelial cells loosen. III. Neutrophils extravasate. IV. Neutrophils phagocytose invading microbes.

As described in the animation, the inflammatory response depends on the interaction of many inflammatory molecules and cellular proteins. List the pairs of molecules or cells that interact. I. Endothelial prostaglandins II. Neutrophil integrins III. Endothelial selectin

I. Nerve cells II. Endothelial ICAM III. Neutrophil surface carbohydrates -Endothelial VCAM interacts with neutrophil integrins to lock the neutrophil into place so that the neutrophil can extravasate. VCAM has the same function as ICAM. It does not interact with mast cells.

List the steps of phagocytosis.

I. Phagocyte pseudopods clasp and engulf the microbe. II. The microbe is trapped within a phagosome. III. A lysosome fuses with the phagosome, forming a phagolysosome. IV. Enzymes cleave macromolecules and generate reactive oxygen species, destroying the microbe. V. The microbial debris is released from the cell.

The five classic signs of localized inflammation are redness, warmth, pain, swelling, and altered function at the affected site. Altered function is caused when swelling interferes with the movement and function of the inflamed area. Match the signs to their causes: I. Swelling II. Warmth III. Redness IV. Pain

I. increased vascular permeability II. caused by vasodilation III. increased blood flow to the site IV. increased production of prostaglandin

Pyrogens indirectly cause the hypothalamus to...

Increase the temperature set point. -Pyrogens are fever-causing compounds that increase the temperature set point.

Extravasation of immune cells depends on:

Increased permeability of endothelial cell junctions. -Extravasation of immune cells depends on increased permeability of endothelial cell junctions and increased vasodilation. Antibodies are NOT necessary for extravasation. Selecting expression is increased prior to extravasation.

The two following statements are examples of the connections between.... 1. Macrophages ingest and degrade microbes and present the microbial antigens to other immune system cells. 2. Antibodies on the surface of virally infected host cells activate natural killer (NK) cells.

Innate and adaptive branches of immunity. -Phagocytosis by macrophages is an innate response. Presentation of the degraded microbial antigens activates the adaptive response. NK cells are nonspecific, innate cells. They are activated by antibodies of adaptive immunity.

List the description of Innate Immunity.

Involves physical barriers. Is nonspecific. Includes the alternate complement pathway. Is triggered by peptidoglycan and lipopolysaccharide.

List the description of Adaptive Immunity.

Involves specific antigens. Involves memory cells. Produces antibodies. Reacts more slowly during the initial infection.

The immune system...

Is a system that differentiates self from non self to neutralize harmful invaders. -The immune system is composed of organs, cells, proteins, and other defenses from pathogens and other substances. All aspects recognize self versus non self, but some arts in different ways and with different levels of specificity.

Which is true of the normal intestinal microbiota?

It can help aid digestion and absorption of nutrients. -Some intestinal microbes secrete enzymes that break down complex carbohydrates into forms humans can absorb. Hundreds of different species, including yeasts and protists, can be present. The microbes can be a problem, causing possible infection in the host, if they colonize a different tissue.

How does the alternative complement pathway kill the invading microbial cell?

It destroys the proton motive force required for energy production. -In the alternative complement pathway, complement proteins form membrane attack complexes, or MACs, in the membrane of the invading microbe. The MACs form pores, which destroy the membrane integrity and in so doing destroy the proton motive force necessary for the microbe to produce energy. The proton motive force depends on a gradient of protons, which cannot be formed when the semipermeability of the microbe is destroyed by the MAC pores. Without the proton motive force, the microbe cannot produce ATP and dies.

How does a moderate fever slow bacterial growth?

It produces suboptimal temperatures for the microbe. -Most human pathogens grow best at body temperature. Therefore, increasing body temperature through fever slows bacterial growth because it produces suboptimal growth conditions.

List the protective compounds of the gastrointestinal tract.

M cells. -M cells are found in the intestines. They take up microbes and release them into a pocket to be destroyed by immune cells.

Which cell type dispersant in gut-associated lymphoid tissue (GALT) and takes up microbes, releasing them into pockets containing macrophages?

M cells. -M cells take up intestinal microbes and release them on the basolateral side of the cell into a pocket. Once there, macrophages destroy the microbes through phagocytosis and present their antigens to adaptive immune cells.

Moderate fever can actually be beneficial because it...

Moves the temperature outside the pathogens' optimal range. -If a pathogen grows more slowly there is more time for the immune system to respond and control the pathogen to reduce the infection. Increasing temperature outside the optimal and reducing iron availability can slow growth. Enzymatic denaturation might occur in the host as well as the pathogen and likely not possible wit moderate fever. Inflammation is not directly related to fever.

What cell type is shown in the figure?

Neutrophil. -Neutrophils are a type of polymorphonuclear leukocyte (PMN), characterized by multilobed nuclei. Macrophages and dendritic cells are white blood cells with a single nucleus that is not multilobed.

Innate immunity is also called _________ immunity.

Nonadaptive.

Microbial species of the microbiota may interfere with colonization of pathogens by all EXCEPT which mechanism?

Phagocytosis. It can through: -competition for attachment receptors on host cells -through the synthesis of antimicrobial compounds -competition for food sources --Commensal species may limit pathogen colonization via competition for resources (space and food) or by synthesizing antimicrobial compounds. Phagocytosis occurs as part of the host immune response.

Which activates a natural killer (NK) cell to kill a host cell?

Presence of antibodies on the host cell. Absence of MHC I on the host cell. -The absence of MHC I on the host cell activates the NK cell to kill it. MHC I identifies self. When a cell loses expression of MHC I, usually because it has transformed into a cancer cell, the NK cell no longer recognizes it as self and destroys it. The presence of antibodies on the host cell also activates the NK cell. Viral proteins are frequently embedded in the membrane of virally infected cells. Antibodies specific to those viral proteins coat the infected cell. The presence of these antibodies then stimulates the NK cell to kill the host cell.

Complement protein factor C3b is an opsonin, which means it can...

Promote phagocytosis. -Some complement factors are T and trigger degranulation and stimulate chemotaxis. If C3b binds to LPS, it will trigger the complement cascade and many additional factors form a MAC, but by itself it will promote phagocytosis.

The gut microbiome benefits the host in many ways. One benefit of the gut microbiome is that it helps to prevent infection by pathogenic microbes. To directly compete with and inhibit the growth of pathogenic microbes, members of the gut microbiome do which of the following?

Secrete substances that inhibit the growth of pathogens. Compete for nutrients. Occupy attachment receptors. -Members of the gut microbiome prevent colonization by pathogens by competing for nutrients and attachment receptors. They also directly inhibit the growth of pathogens with secreted antimicrobial substances. The gut microbiome can also degrade mucin rejuvenating the protective mucin layer of the host's gut, degrade complex carbohydrates so that the host can better absorb them, and synthesize vitamins that the host cannot make. These actions benefit the host, but they do not directly inhibit pathogen growth.

Bradykinin plays several roles in inflammation. According to the figure, which of the following is not a function of bradykinin in inflammation?

Stimulating the release of cytokines by macrophages. -**

Which complement cascade pathway depends on the production of antibodies?

The classical pathway. -Both the alternate pathway and lectin pathway are components of the innate immune system and do not require antibodies. Only the classical pathway requires prior antibody production. CD47 paralyzes phagocytes to prevent phagocytosis of host cells.

Pseudomembranous enterocolitis is caused by an overgrowth of the bacteria Clostridioides difficile. This overgrowth can be caused by antibiotic therapy in which sensitive members of the microbiome are killed or inhibited by the antibiotic drug, but the resistant C. difficile is not. Because the C. difficile infection is resistant to many antibiotics, it is hard to treat. Cases of pseudomembranous enterocolitis have been cured with fecal transplants in which the gut microbiome of a donor healthy person is transferred into the patient. Fecal transplants work to cure this resistant infection because...

The donor's healthy microbiome outcompetes the C. difficile and restores balance to the gut microbiome in the patient.

Which is true of macrophages?

They are the cells most likely to first encounter an invading pathogen. -Macrophages, capable of phagocytosis, are the cells most likely to first encounter invading microbes. Although they do not produce antibodies, they act as antigen-presenting cells and hence function in adaptive immunity.

Which are true regarding macrophages?

They present microbial peptide antigens on major histocompatibility complexes. They are phagocytic. They differentiate only from monocytes.

Which is a physical barrier to microbial infection in innate immunity?

Tightly linked epithelial cells. -Tightly linked epithelial cells are a physical barrier. Acidic pH, superoxide radicals, and antimicrobial peptides are all chemical barriers.

Which receptors on host cells participating in innate immunity recognize bacterial proteins?

Toll-like receptors. -Different Toll-like receptors recognize different bacterial proteins to help aid the immune response. CD47 is a human cell membrane glycoprotein that prevents cell phagocytosis by host immune cells. Fc receptors recognize the constant region of human antibodies. MHC receptors are self-markers.

Interferons are cytokines produced by host cells in response to intracellular infection. There are two types of interferons, type I and type II. What is a difference between these two types?

Type I interferes with viral replication, while type II activates white blood cells. -Type I interferon binds to uninfected host cells, causing expression of antiviral proteins in those cells that interfere with viral replication. Type II activates white blood cells and increases the number of major histocompatibility complexes on their surface.

Which host cell products prevents viral infections by inhibiting viral replication?

Type I interferons. -Type I interferons prevent viral infection of host cells by activating the expression of both endoribonucleases that cleave viral RNA and protein kinases that prevent the translation of viral RNA. Type I interferons are produced and secreted by virally infected host cells to protect uninfected cells. They are also used as a medication to treat certain viral infections such as hepatitis C. Type II interferons, Toll-like receptors, and NOD-like receptors do not directly inhibit viral replication within a host cell. Type II interferon activates white blood cells. Both the Toll-like receptors and NOD-like receptors alert the immune system to the presence of pathogens.

A Streptococcus pneumoniae mutant does not produce a capsule. What will be the most likely result of this mutation if the bacteria infect a host?

Without the capsule, opsonization of the mutant will not be required for host macrophages to ingest the microbe, making it less pathogenic. -Capsules are antiphagocytic coatings that make it difficult for the phagocyte pseudopods to clasp the microbe. As a result, encapsulated microbes must first be opsonized with antibodies or complement proteins before phagocytosis can occur. The presence of antibodies or complement facilitates the adherence of the phagocyte to the microbe and allows ingestion. Without the capsule, phagocytes can clasp and destroy the microbe more easily and the microbe is less pathogenic.