Immunology Chapter 2: Adaptive Immunity

Study Notes

Adaptive immunity involves specificity for particular foreign molecules (antigens) and memory for most previously encountered antigens.
Memory response is faster and greater than the initial response.

B cells are activated by antigens and differentiate into plasma cells that secrete antibodies.
Antibodies bind to antigens and neutralize them or mark them for destruction by other cells.
Memory B cells are formed, providing long-term immunity.

Cytotoxic T cells kill virus-infected cells and some cancer cells.
Helper T cells activate other immune cells, including B cells and cytotoxic T cells.
Memory T cells are formed, providing long-term immunity.

Exogenous antigens are taken up by APCs, broken down into peptides, and bound to MHC-II molecules.
MHC-II/peptide complex is recognized by Helper T cells, which then become activated.
Endogenous antigens are generated from within the cell, broken down into peptides, and bound to MHC-I molecules.
MHC-I/peptide complex is recognized by cytotoxic T cells.

Antibodies (immunoglobulins) have a single-unit structure with antigen binding sites, light and heavy chains, and variable and constant domains.
Antibody classes include IgG, IgA, IgM, IgE, and IgD, each with distinct functions and characteristics.

IgG: neutralizes bacterial and viral toxins, enhances phagocytosis, activates complement, and crosses the placenta for fetal immunity.
IgA: protects mucus membranes against adhesion of virus and bacteria.
IgM: activates complement, causes agglutination and lysis of bacteria, and is the first antibody to be secreted by plasma cells.
IgE: involved in allergic reactions and defence against parasites.
IgD: found on the surface of B-cells as an antigen receptor.

Immunological memory involves thousands of memory cells that exist after initial encounter with an antigen.
Memory cells can proliferate and differentiate within hours upon subsequent exposure to the same antigen.
Serum IgG antibody titers are much higher and faster on the second response.