immunoglobulinT

Immunoglobulin T (IgT) is an immunoglobulin isotype described in jawed vertebrates, most prominently in teleost fish. In some species it is also referred to as IgZ. IgT is structurally related to other heavy-chain immunoglobulins but is distinct in its genetic loci and expression patterns. It has been identified in several fish lineages, including rainbow trout and zebrafish, where the IgT-producing B cells are characterized by their unique mucosal distribution.

IgT is predominantly associated with mucosal immunity. In teleosts, IgT-producing B cells are enriched in mucosal tissues such as the gut, skin, and gills, and IgT is secreted into the mucus layer of these surfaces. By contrast, systemic immunity in many species relies more on IgM. The transport of IgT into mucosal secretions is linked to mucosal transport mechanisms, including processes analogous to the secretory pathway described for other vertebrate antibodies, enabling IgT to reach the external environment of these tissues.

Functionally, IgT appears to play a major role in defense against pathogens at mucosal interfaces. Mucosal infections often elicit IgT-dominated antibody responses, with IgT capable of binding to and neutralizing pathogens, as well as contributing to the regulation of the commensal microbiota in the mucosal niche. This mucosal specialization supports the concept that IgT serves a role analogous to mammalian IgA in protecting external body surfaces.

Evolutionarily, IgT is not present in all vertebrates; mammals lack an IgT isotype. Across fish, the IgT/IgZ class shows species-specific variations in gene organization and expression, reflecting diverse mucosal immune strategies. Ongoing research continues to clarify its precise functions and evolution.