Chapter 15
The CD4 coreceptor is expressed on T __________ cells.
CD4 is an accessory receptor protein on T HELPER cells that binds to MHC class II molecules. CD8 is found on cytotoxic T cells, and it binds MHC class I molecules. T cells constantly circulate between the lymphatic and general circulatory systems, migrating to specific T-cell areas of the lymph nodes and spleen.
The CD8 coreceptor is found on the surface of which cell type?
CD8 is found on CYTOTOXIC T CELLS, and it binds MHC class I molecules. T cells constantly circulate between the lymphatic and general circulatory systems, migrating to specific T-cell areas of the lymph nodes and spleen.
Specific immune globulin is derived form patients who:
Companies that prepare SIG obtain serum from patients who are CONVALESCING FROM THE DISEASE AND ARE IN A HYPERIMMUNE STATE (the serum of pts in this state contains high titers of antibodies) after such infections as pertussis, tetanus, chickenpox, and hepatitis B. These globulins are preferable to ISG because they contain higher titers of specific antibodies obtained from a smaller pool of patients.
Specific immune globulin (SIG) preparations contain a __________ antibody titer than those concentrations found in immune serum globulin (ISG)
Companies that prepare SIG obtain serum from patients who are convalescing and in a hyperimmune state after such infections as pertussis, tetanus, chickenpox, and hepatitis B. These globulins are preferable to ISG because they contain HIGHER titers of specific antibodies obtained from a smaller pool of patients.
T-cell-independent antigens are usually simple molecules such as lipopolysaccharide or __________ with many repeating and invariable determinant groups.
A few antigens can trigger a response from B lymphocytes without the cooperation of APCs or T helper cells. These are called T-cell-independent antigens and are usually simple molecules such as carbohydrates with many repeating and invariable determinant groups
A molecule that stimulates a specific response by T and B cells are called a(n) __________ or ___________
ANTIGEN (Ag), or IMMUNOGEN, is the name we give to these chemical substances to which the immune response reacts. They are molecules that stimulate a response by T and B cells. They are usually protein or polysaccharide molecules on or inside all cells and viruses, including our own. Environmental chemicals can also be antigens. In fact, any exposed or released protein or polysaccharide is potentially an antigen, even those on our own cells. For reasons we discuss later, our own antigens do not usually evoke a response from our own immune systems.
Exposing a person to the antigenic components of a microbe without its pathogenic effects for the purpose of inducing a future protective response is called __________
Active immunity can be conferred artificially by VACCINATION—exposing a person to material that is antigenic but not pathogenic
Antigens that enter the body intravenously become localized in the
Antigens introduced intravenously travel through the bloodstream and end up in the liver, spleen, bone marrow, kidney, and lung
Antigens stimulate _________ that have specific receptors for that antigen
B CELLS AND T CELLS; antigens stimulate the multiplication of lymphocytes that have specific receptors for that antigen. Specifically for a single antigen is progammed into the lymphocyte and is set for the life of the cell.
Lymphocyte antigen receptor diversity is due to random genetic __________ events.
By the time T and B cells reach the lymphoid tissues, each one is already equipped to respond to a single unique antigen. This amazing diversity is generated by extensive DNA REARRANGEMENTS of more than 500 gene segments that code for the antigen receptors on the T and B cells
An antibody molecule is made up of
two identical heavy chains and two identical light chains.
T cells in the lymphoid organs are:
mature and primed to react with presented antigens
__________ immunity can last from a few months to a lifetime
natural active
Circulating maternal IgG antibodies crossing the placenta is an example of __________ immunity.
natural passive
Following the binding of antigen and receipt of interleukin messages from T helper cells, B cell activation signals are sent to the B cell _________
nucleus
During the generation of lymphocyte receptor diversity, any cells that develop a specificity for _________ MHC molecules are eliminated.
self
__________ techniques that are based on isolating microbe genes are being employed in vaccine development.
GENETIC ENGINEERING; Genetic engineering provides a m eans of isolating the genes that encode various microbial antigens, inserting them into plasmid vectors, and cloning them in appropriate hosts.
Most B cells must interact with T __________ cells that bear receptors for epitopes on the same antigen to become functional.
HELPER; The Activation of B Cells: Clonal Expansion and Antibody Production The activation of B cells by most antigens (T-dependent antigens) involves a series of events: 1. Binding of antigen 2. Antigen processing and presentation 3. B cell/T HELPER cell cooperation and recognition 4. B-cell activation Differentiation 5. Clonal expansion. The primary action of plasma cells is to secrete into the surrounding tissues copious amounts of antibodies with the same specificity as the original receptor. Although an individual plasma cell can produce around 2,000 antibodies per second, production does not continue indefinitely. The plasma cells do not survive for long and deteriorate after they have synthesized antibodies.
Cytotoxic T cells kill __________ cells and __________ host cells.
How T Cells Respond to Antigen: Cell-Mediated Immunity (CMI): T-cell types and responses are extremely varied. When activated (sensitized) by antigen, a T cell gives rise to one of three different types of progeny, each involved in a cell-mediated immune function. The three main functional types of T cells are 1. helper T cells that activate macrophages, assist B-cell processes, and help activate cytotoxic T cells; 2. regulatory T cells that control the T-cell response; and 3. cytotoxic T cells that lead to the destruction of INFECTED HOST CELLS and other "FOREIGN" CELLS.
__________ __________ __________ (ISG) is used for passive immunization and contains immunoglobulin extracted from the pooled blood of many human donors.
IMMUNE SERUM GLOBULIN (ISG), sometimes called gamma globulin, contains immunoglobulin extracted from the pooled blood of human donors. The method of processing ISG concentrates the antibodies to increase potency and eliminates potential pathogens (such as the hepatitis B and HIV viruses).
The ability of the body to recognize and react with mutliple foreign substances is ___________
IMMUNOCOMPETENCE: the ability of the body to recognize and react with mutliple foreign substances
B cells recognize antigen using their specific B cell receptor, which is the ___________ it will secrete once clonal selection has taken place.
IMMUNOGLOBULIN are large molecules that serve as the antigen receptors of B cells and, if they are secreted, as antibodies. The basic immunoglobulin molecule is a composite of four polypeptide chains: a pair of identical heavy (H) chains and a pair of identical light (L) chains. One light chain is bonded to one heavy chain, and the two heavy chains are bonded to one another with disulfide bonds, creating a symmetrical, Y-shaped arrangement.
Due to hypersensitivity reactions to antibodies from horse serum, antibodies for artificial passive immunity are derived from:
Immune serum globulin (ISG), sometimes called gamma globulin, contains immunoglobulin extracted from the POOLED BLOOD OF HUMAN DONORS. The method of processing ISG concentrates the antibodies to increase potency and eliminates potential pathogens (such as the hepatitis B and HIV viruses).
Vaccination programs protect individuals within a population, both directly and indirectly due to the concept of _________ __________.
In effect, collective immunity through mass immunization confers indirect protection on the nonimmune members (such as nonvaccinated children). HERD IMMUNITY maintained through immunization is an important force in preventing epidemics but relies upon the willingness of the majority to be vaccinated in order to keep the population safe. It is not just that "the needs of the many outweigh the needs of the few
B cells that have made it through the maturation process have not yet encountered antigen so they are called __________ B cells and they enter circulation in order to home in on specific sites.
In humans, B cells mature in the bone marrow. These NAIVE lymphocytes circulate through the blood, "homing" to specific sites in the lymph nodes, spleen, and other lymphoid tissue, where they take up residence. Here they will come in contact with antigens throughout life. B cells have immunoglobulins as surface receptors
Activated T cells differentiate into cytotoxic T cells if they possess the CD8 marker and react to antigen plus MHC class __________ molecules and into T helper cells if they possess CD4 markers and react to antigen plus MHC class __________ molecules
In summary, mature T cells in lymphoid organs are primed to react with antigens that have been processed and presented to them by an antigen-presenting cell. They recognize an antigen only when it is presented in association with an MHC carrier. T cells with CD4 receptors recognize peptides presented on MHC-II, and T cells with CD8 receptors recognize peptides presented on MHC-I.
After recovery from an infectious disease, the resistance to reinfection is called _________ immunity
NATURAL ACTIVE; After recovering from infectious disease, a person will generally be actively resistant to reinfection for a period that varies according to the disease.
complications associated with vaccines
Relatively rare reactions (about 1 case out of 220,000 vaccinations) are PANENCEPHALITIS (from measles vaccine), BACK-MUTATION TO A VIRULENT STRAIN (from polio vaccine), and NEUROLOGICAL EFFECTS of unknown cause (from pertussis and swine flu vaccines). Some patients experience ALLERGIC RXNS to the medium in which the vaccine strain was cultivated (eggs or tissue culture) rather than to vaccine antigens. When known or suspected adverse effects have been detected, vaccines are altered or withdrawn.
Mature T cells constantly circulate between
T cells constantly circulate between the LYMPHATIC AND GENERAL CIRCULATORY SYSTEMS, migrating to specific T-cell areas of the lymph nodes and spleen
According to the clonal selection theory, there are _________ of lymphocytes generated with unique antigen specific receptors.
TRILLIONS; By the time T and B cells reach the lymphoid tissues, each one is already equipped to respond to a single unique antigen. This amazing diversity is generated by extensive DNA rearrangements of more than 500 gene segments that code for the antigen receptors on the T and B cells. In time, every possible recombination occurs, leading to a huge assortment of lymphocytes. Estimates of the theoretical number of possible variations that may be created vary from 1014 to 1018 different specificities. Each genetically unique line of lymphocytes arising from these recombinations is termed a clone.
The _________ __________ site or FAb of an antibody is the end of the antibody that specifically recognizes antigen
The ends of the forks formed by the light and heavy chains contain pockets called the ANTIGEN BINDING sites. These sites can be highly variable in shape to fit a wide range of antigens. This extreme versatility is due to variable regions (V) in antigen binding sites, where amino acid composition is highly varied from one clone of B lymphocytes to another, a result of the genetic reassortment we discussed earlier. The remainder of the light chains and heavy chains consist of constant (C) regions whose amino acid content does not vary greatly from one antibody to another.
T cell maturation is directed by the __________ gland and the __________ that it produces.
The maturation of most T cells and the development of their specific receptors are directed by the THYMUS and its HORMONES. Other T cells reach full maturity in the gastrointestinal tract.
One problem with therapeutic antiserum and antitoxins from horses is that horse antigens can stimulate __________
Unfortunately, the presence of horse antigens can stimulate such as serum sickness or anaphylaxis
An antibody has a symmetrical _________ shape
Y
Activated B cells (plasma cells) secrete immunoglobulins otherwise known as __________
antibodies
B cells can act as ________ ________ ________ (APCs) due to the fact that antigen bound to the lg receptor is endocytosed, processed, and presented with MHC class II molecules.
antigen-presenting cells (APCs).
Antigen
any cell, particle, or chemical that induces a specific immune response by B cells or T cells and can stimulate resistance to an infection or a toxin.
The activation of B cells by antigen involves the __________ __________ of a B cell bearing the complementarty antigen-specific receptor
clonal selection; The activation of B cells by antigen involves the CLONAL SELECTION of a B cell bearing the complementary antigen-specific receptor.
A colony of cells derived from a single cell that share identical characteristics are called a(n) __________
clone
Vaccinations, like natural active immunity, vary in:
degree and length of protection