DIFFERENTIAL EXPRESSION OF CD8 EPITOPES AMONGST PORCINE CD8-POSITIVE FUNCTIONAL LYMPHOCYTE SUBSETS

The swine is a useful model for immunobiological studies as it has a h ighly heterogeneous lymphocyte pool, containing several subsets not ea sily accessible in humans and rodents. In particular, the CD8-positive (CD8(+)) cells contain a variety of lymphocyte subsets, such as alpha beta-T cells, gamma delta-T cells, CD4 CD8 double-positive (DP) cells and natural killer (NK) cells. In order to define these subsets furth er, we have selected four monoclonal antibodies (mAb) with differentia l reactivity on CD8(+) cells. Thus, mAb CD8.1 (PPT20) bound to CD8(hi) and CD8(lo) subpopulations in a similar way to the conventional anti- CD8. The mAb CD8.2 (PPT21), though binding to all of the CD8(+) cells, reacted preferably with CD8(hi). Two other mAb, CD8.3 (PPT22) and CD8 .4 (PPT23), were specific for CD8(hi) alpha beta-T-cell subpopulation. These results, complemented by immunoprecipitation, co-modulation and enzyme-linked immunosorbent assay experiments, suggest that CD8.1 and CD8.2 react putatively with the CD8 alpha-chain and CD8.3 and CD8.4 w ith the CD8 beta-chain. Tissue distribution studies revealed that CD8( +) thymocytes and peripheral CD8(hi) alpha beta-T cells expressed both putative CD8 alpha- and beta-chains while peripheral CD4(+)CD8(+) alp ha beta-T cells, CD8(lo) gamma delta-T cells and NK cells expressed on ly putative CD8 alpha-chain. Functional studies indicated that the CD8 (hi) alpha beta-T and CD8(lo) gamma delta-T cells were effector cells in the CD3-redirected cytotoxicity.