Gut intraepithelial T lymphocytes.

The gut mucosa, given its length, contains a very large number of T lymphocytes in the Peyer's patches and disseminated all along the mucosa. The most conspicuous element of this last compartment, the gut intraepithelial lymphocytes, represents a population of CD8+ T lymphocytes as large as that found in the largest lymphoid organ, the spleen. In spite of their numerical importance and the fact that they are in the immediate vicinity of the largest permanent antigenic stimulus in the whole organism, these cells have remained for a long time, paradoxically, the least understood of the lymphocyte populations, in their ontogeny and physiological role. It is becoming increasingly apparent that they are ontogenically more complex than the bulk of the T lymphocytes present in the lymphoid organs and are probably able to recognize a larger array of antigenic determinants than the peripheral CD8+ T lymphocytes.