Functional characterization of porcine CD4(+)CD8(+) extrathymic T lymphocytes

The porcine immune system is unique in that the expression of CD4 and CD8 antigens defines four subpopulations of resting, extrathymic (CD1(-)) T lymphocytes, In addition to CD4(-)CD8(+) and CD4(+)CD8(-) T lymphocytes, CD4(-)CD8(-) and CD4(+)CD8(+) lymphocyte subpopulations are prominent in blood as well as in lymphoid tissues, In the present study, a functional comparison was made between CD4(+)CD8(-) and CD4(+)CD8(+) T lymphocyte subpopulations. In a primary in vitro immune response against alloantigenic stimulator cells, both subpopulations proliferated without significant differences in their reactivity, Different results were obtained when analyzing the antigen-specific functions of the two CD4(+) subpopulations in a secondary response against recall viral antigen; these experiments were performed with T lymphocytes from pseudorabies virus-immunized pigs, The proliferative response against viral antigens could be assigned to the CD4(+)CD8(+) subpopulation, whereas the CD4(+)CD8(-) subpopulation remained nonreactive. Further analyses of the virus-specific in vitro immune response revealed a major histocompatibility complex (MHC) class II restricted helper T lymphocyte reaction involving CD4 but not CDS molecules as restriction elements, Taken together, these results demonstrate that only the extrathymic CD4(+)CD8(+) T lymphocyte subpopulation of swine contains MHC class II-restricted antigen-specific memory T helper cells. (C) 1996 Academic Press, Inc.