– Immunology

Helper T cells (CD4)

• Release IL-2, which mainly causes maturation of cytotoxic T cells

• Release IL-4, which mainly causes B-cell maturation into plasma cells

• Involved in delayed-type hypersensitivity (brings in inflammatory cells by chemokine secretion)

Suppressor T cells (CD8) – regulate CD4 and CD8 cells

Cytotoxic T cells (CD8) – recognize and attack non–self-antigens attached to MHC class I receptors (eg viral gene products)

Intradermal skin test (ie TB skin test) – used to test cell-mediated immunity

Infections associated with defects in cell-mediated immunity – intracellular pathogens (TB, viruses)

B CELLS (BONE) – ANTIBODY-MEDIATED IMMUNITY (HUMORAL)

IL-4 from helper T cells stimulates B cells to become plasma cells (antibody secreting)

MHC CLASSES

MHC class I (A, B, and C)

• CD8 cell activation

• Present on all nucleated cells

• Single chain with 5 domains

• Target for cytotoxic T cells (binds T cell receptor)

MHC class II (DR, DP, and DQ)

• CD4 cell activation

• Present on antigen-presenting cells (eg monocytes, dendrites)

• 2 chains with 4 domains each

• Activates helper T cells (binds T cell receptor)

• Stimulates antibody formation after interaction with B cell surface IgM

Viral infection – endogenous viral proteins produced, are bound to class I MHC, go to cell surface, and are recognized by CD8 cytotoxic T cells

Bacterial infection – endocytosis, proteins get bound to class II MHC molecules, go to cell surface, recognized by CD4 helper T cells → B cells which have already bound to the antigen are then activated by the CD4 helper T cells; they then produce the antibody to that antigen and are transformed to plasma cells and memory B cells

NATURAL KILLER CELLS

Not restricted by MHC, do not require previous exposure, do not require antigen presentation