Immunology / Serology

Innate immunity is nonspecific, present from birth, rapid, and lacks immunologic memory (barriers, phagocytes, complement, NK cells). Adaptive immunity is antigen-specific, slower on first exposure, and generates memory (T and B lymphocytes).

Neutrophils, monocytes/macrophages, dendritic cells, eosinophils, basophils, mast cells, and natural killer (NK) cells. They provide phagocytosis, inflammation, and early cytotoxicity without prior sensitization.

B cells mediate humoral immunity by differentiating into antibody-secreting plasma cells. T cells mediate cell-mediated immunity: CD4+ helper T cells coordinate responses; CD8+ cytotoxic T cells kill infected cells.

A monomer has two identical heavy chains and two identical light chains joined by disulfide bonds, forming a Y. The Fab regions bind antigen; the Fc region mediates effector functions (complement binding, cell receptor binding).

IgG is the most abundant serum immunoglobulin (~70-75%). It is the only class that crosses the placenta, fixes complement, opsonizes, and predominates in the secondary (anamnestic) response. Monomeric.

IgM is a pentamer (10 antigen-binding sites) joined by a J chain. It is the largest immunoglobulin, the first produced in the primary response, and the most efficient at complement activation. Cannot cross the placenta.