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

First immunoglobulin (Ig) expressed during B cell development (primary response; early antibody)

• Opsonizing (coating) antigen for destruction

• Complement fixation

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

Function unclear; appears to be involved in homeostasis

Mucosal response; protects mucosal surfaces from toxins, viruses and bacteria through either direct neutralization or prevention of binding to mucosal surface

Associated with hypersensitivity and allergic reactions

• Plays a role in immune response to parasites