Abstract
Previously, monoclonal antibody (mAb) 9.3 was shown to react with a major population of human T cells, which include T4+ helper/inducer T cells and T8+ cytotoxic T cells. In this investigation mAb 9.3 was shown to precipitate a disulfide-bonded dimer of a 44 kilodalton polypeptide. Comodulation experiments showed that this molecule is not linked to T3/Ti or T11 antigens. mAb 9.3 was capable of inducing T cell proliferation in the presence of 12-o-tetradecanoyl phorbol-13-acetate (TPA). This effect was monocyte-independent. T cell activation with mAb 9.3 and TPA was associated with increases in interleukin 2 (IL-2) receptor expression and IL-2 secretion. mAb 9.3 did not activate T cells, even with the addition of IL-1 or IL-2. Modulation of the T3 complex did not abolish mAb 9.3-induced T cell proliferation in the presence of TPA. These results suggest that the 9.3 antigen may serve as a receptor for an activation pathway restricted to a T cell subset.

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