Regulation of helper T cell clone proliferation via the CD2 molecule.

We have investigated the requirements for CD2-induced proliferation of a CD4+, CD8-, CD3+, CD2+ antigen-specific, class II-restricted proliferating cloned cell line. A combination pair of two monoclonal antibodies (MoAb) recognizing, respectively, TII1 and D66 epitopes on the CD2 molecule was used as a stimulus. The regulatory function of accessory cells and various interleukins in this proliferation was determined. The results show that although this clone was able to proliferate in the absence of accessory cells (AC) or interleukin 1 (IL-1) when stimulated by these MoAb, AC constantly enhanced the response to these MoAb. AC acted by increasing high-affinity IL-2 receptor expression. On the contrary they did not play any role in IL-2 production. This regulation of IL-2 receptor expression by AC was specific of adherent cells, did not involve Fc receptors, was impaired when AC were metabolically inactivated and did not require T cell-AC interaction via LFA1, CD4, or HLA molecules. The AC function was not abrogated by anti-IL-1 antibodies and could not be replaced by exogenous IL-1. These results were compared to previously described AC effects on resting T-cell proliferation when stimulated with the same pair of anti-CD2 MoAb. Clear differences in activation requirements in resting and activated T cells via CD2 molecules were found.