FUNCTIONAL-CHARACTERIZATION OF PORCINE CD4(-LYMPHOCYTES()CD8(+) EXTRATHYMIC T)

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 lymp hocytes, CD4(-)CD8(-) and CD4(+)CD8(+) lymphocyte subpopulations are p rominent 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 proliferat ed without significant differences in their reactivity, Different resu lts were obtained when analyzing the antigen-specific functions of the two CD4(+) subpopulations in a secondary response against recall vira l antigen; these experiments were performed with T lymphocytes from ps eudorabies virus-immunized pigs, The proliferative response against vi ral antigens could be assigned to the CD4(+)CD8(+) subpopulation, wher eas the CD4(+)CD8(-) subpopulation remained nonreactive. Further analy ses of the virus-specific in vitro immune response revealed a major hi stocompatibility 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 C D4(+)CD8(+) T lymphocyte subpopulation of swine contains MHC class II- restricted antigen-specific memory T helper cells. (C) 1996 Academic P ress, Inc.