Which specific class of immunoglobulins is secreted as a pentameric macromolecular structure and constitutes the primary antibody produced during the initial humoral immune response to invading antigens?

💡 Solution & Explanation

Immunoglobulin M circulates as a pentamer linked by a J chain, making it exceptionally effective at agglutination and complement activation during the early stages of primary immune responses. Immunoglobulin G is the most abundant monomeric antibody providing long-term systemic immunity and placental transfer. Immunoglobulin A predominates in mucosal secretions, tears, and colostrum. Immunoglobulin E mediates allergic hypersensitivity reactions and defense against parasitic helminths. Class switching later prompts plasma cells to secrete other antibody isotypes.