Differential activation requirements associated with stimulation of T cells via different epitopes of CD3

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Abstract
A panel of monoclonal antibodies directed to different epitopes of porcine CD3 were employed to investigate stimulation requirements of porcine T lymphocytes. It was found that epitope specificity was an important property of the anti‐CD3 antibodies that determined the requirements for T‐cell proliferation. Thus, T‐cell proliferation induced by triggering different CD3 epitopes showed three different requirements: (a) proliferation induced by the most insensitive epitope required both epitope ligation and some unknown additional signal(s); (b) proliferation induced by the most common epitopes only required epitope ligation, either by monocytes or by immobilization; (c) proliferation induced by the most sensitive epitope required neither epitope ligation nor participation of antigen‐presenting cells (APC). These findings may help to explain the previous confusion over the requirements for T‐cell activation through the CD3 pathway. Finally, the above conclusions apply only to αβ T cells, as porcine γδ T cells, either in bulk culture or isolated, did not proliferate in response to anti‐CD3 stimulation. Therefore, the mechanism underlying γδ T‐cell activation may be different from that of αβ T cells.