Phenotypic classification of porcine lymphocyte subpopulations in blood and lymphoid tissues

Abstract

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 αβ T cells consisted of four subsets (CD4+8-, CD4+8(lo), CD4-8(lo), and CD4-8(hi)) and γδ 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 αβ 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 γδ T cells and the non-T-non-B lymphocytes in the lymph nodes and tonsil were much lower and the majority of the γδ 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 αβ and γδ T cells, demonstrated the T-cell nature of the unique CD4+8+ subset of peripheral lymphocytes, revealed the high heterogeneity of the CD8+ cells, and established the phenotype of NK cells. The functional properties of these defined porcine lymphocyte subsets can now be experimentally determined in health and disease.