Immune Responses

Study Guide 8

Distinguish between humoral immunity and cell-mediated immunity.

H Humoral response: B-cell activation, result from the production of antibodies that circulate in plasma/lymph. Against free bacteria, toxins and viruses in body fluids
Cell-mediated immunity: T-cell activated, works against viruses and bacteria within cells, also against fungi, protozoa and parasitic worms.
Transplanted tissue will mount a T-cell attack.

Describe the function of T-helper cells:

T-helper cells bind to class II MHC-antigen complexes, the T-helper cell proliferates and differentiates into a clone of activated helper T cells and memory helper T cells. Activated T-helper cells secrete cytokines to stimulate other lymphocytes.

Describe the functions of the proteins CD8 and perforin.

CD8 is found on cytotoxic T cells and binds class I MHC proteins, this functions to keep the Tc cell in contact with the infected cell.

Perforin is a protein released by Tc cells and it makes holes in the membrane of the target cell.

Explain how cytotoxic T cells and natural killer cells defend against tumors.

Tumor cells also present abnormal antigens in class I MHC complexes that Tc cells recognize and target. If class I MHC proteins are reduced by the cancer or virus and Tc cells do not detect them, then natural killer cells can lyse these cells.

Explain how antibodies interact with antigens.

The variable region of the antibody binds to the epitope of the antigen.

Diagram and label the structure of an antibody and explain how this structure allows antibodies to (a) recognize and bind to antigens and (b) assist in the destruction and elimination of antigens.

Distinguish between the variable (V) regions and constant (C) regions of an antibody molecule.

Variable region – the amino acid sequences vary from antibody to antibody, bind the antigenic epitope

Constant region – sequence varies little between antibodies, controls distribution within body and mediates antigen disposal.

Compare the processes of neutralization, opsonization, agglutination, and complement fixation.

Neutralization – antibody binds to an blocks the activity of the antigen

Opsonization – antibody binding induces phagocytosis

Agglutination – clumping of bacteria or viruses due to antibody binding results in opsonization.

Complement fixation – activation of the complement system by antigen-antibody complexes.

Immunity in Health and Disease

Distinguish between active and passive immunity and describe examples of each.

Active immunity – naturally acquired immunity either from infection or immunization (e.g., chicken pox exposure, measles vaccine)

Passive immunity – passed from mother to child through placenta or via breast milk

Explain how the immune response to Rh factor differs from the response to A and B blood antigens.

Blood group antigens generate IgM antibodies that do not cross the placenta, whereas Rh antibodies are IgGs that can cross the placenta. Therefore, an Rh- mother with an Rh+ fetus can develop antibodies against the Rh factor and these can cross the placenta and attack red blood cells. An immune memory is created, so that future pregnancies are may be compromised.

Explain what causes anaphylactic shock and how it can be treated.

An acute allergic response can cause a widespread mast cell degranulation resulting in massive histamine production. This causes dilation of peripheral blood vessels and a precipitous drop in blood pressure.

List some known autoimmune disorders.

Systemic lupus erythematosus

Rheumatoid arthritis

Insulin-dependent diabetes mellitus

Multiple sclerosis

Describe the infectious agent that causes AIDS and explain how it enters a susceptible cell.

HIV is a retrovirus that infects cells that have surface CD4 antigens, including helper T-cells, some B lymphocytes and brain cells.