nonIgM

NonIgM refers to immunoglobulin isotypes other than IgM. In humans, the major non-IgM classes are IgG, IgA, IgE, and IgD. B cells can switch from producing IgM to these other isotypes through a process called class switch recombination, which enables antibodies to tailor their effector functions to different pathogens and sites of infection.

IgG is the most abundant serum antibody and provides neutralization, opsonization to promote phagocytosis, and can activate the classical complement pathway. It has four subclasses (IgG1–IgG4) with distinct functional properties and tissue distributions. IgA is the principal antibody at mucosal surfaces; it exists as a serum monomer and as secretory dIgA in mucous secretions, where it often forms dimers linked by a J chain and associated with the secretory component to protect it from degradation. IgA plays a key role in mucosal immunity and pathogen neutralization.

IgE is involved in defense against parasitic infections and mediates allergic responses by binding to FcεRI receptors on mast cells and basophils, triggering release of inflammatory mediators upon antigen interaction. IgD largely serves as a B cell receptor on naive B cells and is present in lower concentrations in serum.

Production and distribution: non-IgM antibodies are produced by plasma cells after somatic hypermutation and affinity maturation, with class switching influenced by cytokines and helper T cell signals. Their serum half-lives, affinities, and tissue localizations differ, shaping the quality of the humoral response.

Clinical relevance: evaluating non-IgM antibodies supports diagnosis of infections, autoimmune diseases, and immunodeficiencies. For example, IgG indicates prior exposure or immunity, IgA antibodies reflect mucosal responses, and IgE levels relate to allergic and parasitic conditions.