Aug 10, 2010 14:48 GMT  ·  By
This is a gut section from an infected fish showing the presence of IgT+ B cells (green) in the epithelium and the parasite C. shasta (magenta)
   This is a gut section from an infected fish showing the presence of IgT+ B cells (green) in the epithelium and the parasite C. shasta (magenta)

A study carried out at the University of Pennsylvania School of Veterinary Medicine has discovered the function of one of the most ancient antibodies in the animal reign, the immunoglobulin that ensures mucosal immunity.

This antibody is very important in the guts of fish and it will help to better understand the human gut immune system and also develop healthier and safer ways of preventing infections in fish.

The study identified the fish antibody IgT as being the most ancient vertebrate immunoglobulin and studied its unique aspects of function and structure, things that were not possible five years ago when the IgT was first discovered.

This discovery tends to contradict the previous theory that says that the specialization of immunoglobulin isotypes into different body areas like the intestines and the blood happened along with the evolution of four-legged animals.

Research also found evidence that a new B cell lineage that produces IgT exists and that in the gut, the IgT+B cells are the prevailing cell subset.

Testing on the rainbow trout showed that its IgT response to an internal parasite were only present in the gut while IgM responses remained into plasma.

Following the theory that IgT has a crucial role in mucosal immunity, researchers found that most trout intestinal bacteria were coated with this antibody, and concluded that the specialization of immunoglobulin isotypes into different places inside the body is a general feature of all jawed vertebrate immune systems, necessary for different exposed body areas that need different immune protection to stay healthy.

Oriol Sunyer, associate professor in the Department of Pathobiology at Penn Vet said that “Immunoglobulins like IgA, IgX and the newly discovered IgT are evolutionarily distant and their specialization into mucosal compartments must have occurred independently by a process of convergent evolution driven by similar selective pressures operating on the gut environment of fish, amphibians and mammals.”

Immunoglobulins first emerged in vertebrates some 400 million years ago when jawed fish appeared and then evolved and diversified into isotypes with specific roles in innate and adaptative immunity in different parts of the body.

The results of the study appear in the online version of Nature Immunology and could be found on the cover of the September issue.