IgG | 76\% | Plasma & interstitial fluid; crosses placenta | Provides baseline immunity to newborn; predominant secondary response |
IgA | 15\% | Breast milk, tears, saliva; mucosal secretions of respiratory, GI, GU tracts | Prevents pathogen adherence/penetration at mucosal surfaces |
IgM | 8\% | Plasma | First Ig produced on initial exposure (primary response) |
IgE | 0.002\% | Plasma & interstitial fluid | Triggers Type I rapid hypersensitivity (allergy, anaphylaxis); defense vs. parasites |
IgD | 1\% | Plasma (B-cell surface) | Plays role in B-cell activation/maturation |