IgT, a primitive immunoglobulin class specialized in mucosal immunity

Abstract

Teleost fish are the most primitive bony vertebrates that contain immunoglobulins. In contrast to mammals and birds, these species are devoid of immunoglobulin A (IgA) or a functional equivalent. This observation suggests that specialization of immunoglobulin isotypes into mucosal and systemic responses took place during tetrapod evolution. Challenging that paradigm, here we show that IgT, an immunoglobulin isotype of unknown function, acts like a mucosal antibody. We detected responses of rainbow trout IgT to an intestinal parasite only in the gut, whereas IgM responses were confined to the serum. IgT coated most intestinal bacteria. As IgT and IgA are phylogenetically distant immunoglobulins, their specialization into mucosal responses probably occurred independently by a process of convergent evolution.

Teleost skin, an ancient mucosal surface that elicits gut-like immune responses

“…Additionally, teleosts contain IgT (also called IgZ in some species), an Ig class first identified in 2005 (7,8). In 2010, we demonstrated that, analogous to mammalian IgA, teleost IgT plays a specialized role in gut mucosal immune responses whereas IgM contributes predominantly to systemic immunity (9). This finding overturned the paradigm that specialized mucosal immunoglobulins arose during tetrapod evolution.…”

Identification and characterization of Bacillus subtilis from grass carp (Ctenopharynodon idellus) for use as probiotic additives in aquatic feed

“…Mucus samples were isolated from the intestines of three grass carps as described by Zhang et al [24]. The protein concentration of the gut mucus was adjusted to 0.5 mg/ml as determined by the Protein Assay kit (BioRad).…”

Characterization of an IgM-like immunoglobulin from silver catfish (Rhamdia quelen) serum and its use for the production of polyclonal antibodies and development of immunoassays

“…In addition, chimeric Ig genes with similarity to other mammalian isotypes, namely IgD and IgT/IgZ, have already been found in a few fish species , Fillatreau et al 2013, Sunyer 2013. Although recent reports point out for a possible involvement in mucosal immunity (Zhang et al 2010, the role of these isotypes in protection is still a matter of debate.…”