Phenotypic classification of porcine lymphocyte subpopulations in blood and lymphoid tissues

The pig is a useful model for the heterogeneity of the mammalian immune system and has also recently received attention as a possible source of organs for human transplantation. Here we report a detailed analysis of porcine lymphocyte phenotypes. Peripheral blood alpha beta T cells consisted of four subsets (CD4(+)8(-), CD4(+)8(lo), CD4(-)8(hi) and CD4(-)8(hi)) and gamma delta T cells of three (CD2(-)4(-)8(-), CD2(+)4(-)8(lo) and CD2(+)4(-)8(-)). There were, in addition, a large proportion of non-T-non-B lymphocytes with CD2(+)3(-)4(-)8(lo) surface immunoglobulin-negative phenotype containing natural killer (NK) activity. A striking observation was the relatively low frequency of alpha beta T cells in the blood of young pigs. Similar phenotypes were also identified in the cells from peripheral lymphoid tissues? though the proportions of the gamma delta T cells and the non-T-non-B lymphocytes in the lymph nodes and tonsil were much lower and the majority of the gamma delta T cells in the lymphoid tissues bore CD2 and/or CD8. In thymus, the small thymocytes were predominantly CD3(-)4(+)8(+) while the mature large thymocytes displayed phenotypes similar to those of peripheral T cells. Thus this work has directly defined porcine alpha beta and gamma delta T cells, demonstrated the T-cell nature of the unique CD4(+)8(+) subset of peripheral lymphocytes, revealed the high heterogeneity of the CDS' cells, and established the phenotype of NK cells. The functional properties of these defined porcine lymphocyte subsets call now be experimentally determined in health and disease.