Microbiology Practice Exam 2025 - Free Microbiology Practice Questions and Study Guide

The immunoglobulin characterized as a dimer is IgA. Immunoglobulin A plays a critical role in mucosal immunity, as it is predominantly found in mucosal areas, such as the gut, respiratory tract, and urogenital tract, as well as in secretions like saliva, tears, and breast milk.

In its dimeric form, two monomeric IgA molecules are linked together by a joining chain (J chain) which enhances its ability to bind to pathogens at mucosal surfaces. This structure allows IgA to effectively neutralize pathogens and prevent their adherence to epithelial cells, thus playing a crucial role in protecting mucosal surfaces from infections.

Other immunoglobulins have different structural forms; for instance, IgM typically exists as a pentamer (five monomer units linked), IgG is primarily a monomer, and IgE also appears as a monomer. Each of these immunoglobulins has unique functions and locations in the immune response, but IgA's dimeric form is specifically suited for its role in mucosal immunity.