Development of γδ thymocyte subsets during prenatal and postnatal ontogeny

In this report, we describe 12 subpopulations of porcine gamma delta thymocytes based on their expression of CD1, CD2, CD4, CD8-isoforms and CD45RC. Our data suggest that gamma delta thymocytes can be divided into two major families: (a) one large family of CD4(-)gamma delta thymocytes that could be further subdivided according to the CD2/CD8 alpha alpha phenotype and (b) a small family of CD4(+)gamma delta thymocytes bearing CD8 alpha beta and possessing certain unusual features in comparison with other gamma delta thymocytes. Maturation of gamma delta thymocytes within the CD4(-) family begins with proliferation of the CD2(+) CD8(-) CD1(+) CD45RC(-)gamma delta common precursor. This developmental stage is followed by diversification into the CD2(+) CD8 alpha alpha(+), CD2(+) CD8(-) and CD2(-) CD8(-) subsets. Their further maturation is accompanied by a loss of expression of CD1 and by increased expression of CD45RC. Therefore, individual subsets develop from CD1(+) CD45RC(-) through CD1(-) CD45RC(-) into CD1(-) CD45RC(+) cells. On the other hand, gamma delta thymocytes within the CD4(+) family bear exclusively CD8 alpha beta, always express CD1, but may coexpress CD45RC. These cells have no counterpart in the periphery. Our observations suggest that all peripheral CD8(+)gamma delta T cells express CD8 alpha alpha and that two subsets of these cells differing in major histocompatibility complex II expression, occur. We propose that one subset acquires CD8 alpha alpha in the thymus while the second acquires CD8 alpha alpha as a result of stimulation in the periphery.