CD8 DIMER USAGE ON ALPHA-BETA AND GAMMA-DELTA T-LYMPHOCYTES FROM EQUINE LYMPHOID-TISSUES

Eight murine monoclonal antibodies (mAb) were used to identify the equ ine CD8 alpha or CD8 beta chains and to define the expression of these chains on lymphocytes from various lymphoid tissues. CD8 alpha was a 39 kDa protein and CD8 beta was a 32 kBa protein. Both chains were exp ressed on most of the CD8(+) T lymphocytes in the peripheral blood, sp leen, thymus, mesenteric lymph nodes and ileal intraepithelial lymphoc ytes (IEL), however, in each lymphoid compartment a percentage of lymp hocytes expressed only the CD8 alpha chain. The lamest percentage of C D8 alpha alpha expressing T lymphocytes was 37.7% of the IELs. Purifie d T lymphocytes from the ileum expressing CD8 alpha beta co-expressed the alpha beta T cell receptor (TCR). In contrast, purified CD8(+) T l ymphocytes from the PBMC co-expressed either the alpha beta or gamma d elta TCR by RT-PCR. Use of pooled anti-CD8 alpha mAb of the murine IgG 2a isotype and rabbit complement resulted in lysis of the entire CD8 e xpressing population in peripheral blood mononuclear cells (PBMC). The se results indicated that CD8 dimer usage by equine T lymphocytes is s imilar to other species and that the mAb described can be further used to separate equine CD8(+) T lymphocyte subsets from the lymphoid tiss ues to define their function in protection against viral and other inf ections.