Antibodies & T-Cells

Humoral immune response

Defense against extracellular antigens; B-lymphocytes become either plasma cells that produce antibodies or memory cells

Antibodies

Immunoglobulins; constant region determines the type (class); variable region determines antigen specificity; 2 heavy chains, 2 light chains

How antibodies work

Neutralize toxins and viruses; agglutinate and precipitate; opsonize (promote phagocytosis); activate complement; mark cells for destruction by NK cells

IgG

Most common class; can cross placenta and protect the fetus via passive immunity

IgM

First responder; pentamer

IgE

Responsible for allergic reactions; binds to mast cells (basophils)

IgA

Secreted; found in mucus, tears, saliva, breast milk

IgD

Found in membranes of B-cells

Cell-mediated immunity

Defense against infected cells; cytotoxic T cells with CD8 receptor for MHC-I recognize infected cells; release perforins and granzymes to destroy infected cells

Cell-mediated immune response

Antigen is engulfed and processed; antigen is presented to Tc cell; Tc is activated; activated Tc binds to abnormal host cells