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Table 2 Major functions of human Ig antibodies [5].

From: An introduction to immunology and immunopathology

Ig antibody Function
IgM First immunoglobulin (Ig) expressed during B cell development (primary response; early antibody)
• Opsonizing (coating) antigen for destruction
• Complement fixation
IgG Main Ig during secondary immune response
• Only antibody capable of crossing the placental barrier
• Neutralization of toxins and viruses
• Opsonizing (coating) antigen for destruction
• Complement fixation
IgD Function unclear; appears to be involved in homeostasis
IgA Mucosal response; protects mucosal surfaces from toxins, viruses and bacteria through either direct neutralization or prevention of binding to mucosal surface
IgE Associated with hypersensitivity and allergic reactions
• Plays a role in immune response to parasites