Resistance and the Immune System: Acquired Immunity

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Resistance and the Immune System: Acquired Immunity

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1. Chapter 21 Resistance and the Immune System: Acquired Immunity

2. 21.1 An Overview of the Acquired Immune Response The ability to eliminate pathogens requires a multifaceted approach. Antigens are microbes or microbe parts that provoke an immune response.

3. The immune system recognizes unique antigenic determinants (epitopes).

4. Immune deficiency is the loss of the body’s ability to respond to antigens and epitopes. Regulatory T cells prevent other T cells from attacking “self” cells. Autoimmune diseases occur when self-tolerance breaks down. If nonimmunogenic molecules (haptens) are linked to proteins, they may not be recognized as “self.” Thus they might provoke an immune response (allergies). Immunological memory is the ability to “remember” past pathogen exposures. The body fights off any subsequent infections.

5. Acquired immunity generates two complementary responses to most pathogens. B lymphocytes (B cells) are involved in producing antibodies against epitopes. T lymphocytes (T cells) provide resistance through lysis of infected or abnormal cells.

6. The humoral immune response involves: activation of B cells. production of antibodies against the identified antigen. If the microbes enter cells, antibodies are useless. Then the cell mediated immune response is activated to eliminate “nonself” cells. T cells control and regulate these activities.

7. Antigen exposure activates only T and B cells with receptors that recognize specific epitopes on that antigen. B and T cell clones contain lymphocytes that develop into: effector cells that target pathogens. memory cells are long-lived B and T cells. They are capable of division on short notice.

9. The immune system originates from groups of stem cells. In the fetus, lymphocytes arise from hematopoietic stem cells in the yolk sac and bone marrow. They develop into: Myeloid progenitors, which become: red blood cells. most white blood cells. Lymphoid progenitors, which become lymphocytes. T lymphocytes are formed in the thymus. B cells are formed in the bone marrow.

11. 21.2 Humoral Immunity Antibodies are of a class of proteins called immunoglobulins. Epitope recognition requires antibodies to have a special structure of: 2 identical heavy (H) chains. 2 identical light (L) chains. Each light and heavy chain has: A constant region, which determines the location and functional class of the antibody. A variable region, which contains different amino acids for the many antibodies produced.

13. The variability allows formation of the specific antigen binding site. The Fab fragment of an antibody combines with the Epitope. The Fc fragment performs functions in: opsonization. activation of the complement system. allergic reactions.

14. There are five immunoglobulin (Ig) classes. IgM is the first (but short-lived) Ig to appear in circulation after B cell stimulation. IgG (gamma globulin) is the major circulating antibody. It provides immunity to the fetus and newborn. IgA provides resistance in the respiratory and gastrointestinal tracts (mucosal immunity). It is found in colostrum. IgE plays a role in allergic reactions. IgD is a cell surface receptor on B cells and activates them.

15. Antibody responses to pathogens are of two types. A primary antibody response occurs the first time the body encounters a pathogen. A secondary antibody response is more powerful and sustained . It occurs with a subsequent infection by the same pathogen.

16. Antibody diversity is a result of gene rearrangements. Somatic recombination is a random mix and match of gene segments. This accounts for the large number of unique antibodies encoded by immune system genes.

17. Antibody interactions mediate the disposal of antigens (pathogens). Formation of antigen-antibody complexes result in the microorganism with the antigen: death. inactivation. increased susceptibility.

18. The membrane attack complex causes cell lysis.

19. 21.3 Cell Mediated Immunity Cellular immunity relies on T-lymphocyte receptors and recognition. Cytotoxic T cells have T-cell receptors (TCRs) and CD8 coreceptor proteins. Naïve T cells have TCRs and CD4 coreceptor proteins. Naïve T cells can help with both humoral and cell mediated immunity. HIV attaches to the CD4 receptor and infects the cell.

20. TCRs and coreceptors allow T cells to recognize and bind to the major histocompatibility complex (MHC). MHC proteins are unique for nearly all individuals. They mark the body’s cells as “self.” Class II MHC proteins on the surface of immune cells present antigen fragments to naïve T cells. They are called antigen-presenting cells (APCs). Class I MHC proteins are found on the surface of nearly all the body’s cells.

21. Naïve T cells mature into effector (helper) T cells.

22. Cytotoxic T cells recognize MHC-1 peptide complexes. Host cells infected by viruses can: degrade viral antigens. present peptide fragments with MHC-1 proteins on the cell surface. Activated cytotoxic T cells recognize and bind to the MHC-1/peptide complex on infected cells. They release toxic substances such as perforin and granzymes to: cause cell death. expose pathogens to antibodies. T cells can also recognize and kill tumor cells.

23. TH2 cells initiate the cellular response to humoral immunity.

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