Antibody classes
MCAT glossary · MCAT
Definition
IgG (most abundant, crosses placenta), IgM (first responder, pentamer), IgA (mucosal, dimer), IgE (allergy, parasites), IgD (B cell receptor).
Antibody classes in plain English
Antibodies are Y-shaped proteins your immune system makes to tag invaders, and they come in five 'classes' (called IgG, IgM, IgA, IgE, IgD) that are like specialists on a team, each stationed where it's needed. IgG is the workhorse — the most common one patrolling your blood, and the only one small enough to cross the placenta and protect a fetus. IgM is the loud first-responder that shows up earliest in an infection (it clumps together as a set of five). IgA guards wet surfaces like your gut, saliva, and tears (travels as a pair); IgE triggers allergies and fights parasites; and IgD mostly sits on B cells as a receptor. A memory trick: the letters G-M-A-E-D spell out roles like 'General, Meets-first, All-the-mucus, Extra-allergy, Doorman.'
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