A monoclonal antibody (H227) recognizing a new epitope of 4F2 molecular complex associated with T cell activation.

We developed and characterized a monoclonal antibody (mAb), H227, recognizing a new epitope of human 4F2 molecular complex whose roles remain to be identified. Both staining patterns and molecular sizes recognized by H227 mAb were the same to those of 4F2 mAb. Thus, both H227 and 4F2 mAbs were reactive to monocytes, thymocytes, and activated lymphocytes and immunoprecipitated the 125-kDa molecular weight membrane protein under nonreducing conditions and 85-kDa heavy-chain and 40-kDa light-chain proteins under reducing conditions. These two mAbs immunoprecipitated only the 85-kDa heavy-chain protein when the cell lysate was initially treated with dithiothreitol. Sequential immunoprecipitation proved their cross-reactivity. Both the mAbs inhibited phytohemagglutinin- or concanavalin A-induced proliferation of peripheral blood mononuclear cells (PBMC). In contrast to these similarities, the pretreatment of cells with one mAb failed to block the reactivity to the other, suggesting that their epitopes were different from each other. Furthermore, only H227 mAb augmented phorbol myristate acetate (PMA)-induced PBMC proliferation in association with increase in interleukin 2 receptor expression. In summary, H227 mAb recognizes a new epitope of 4F2 heavy chain that might be involved in the PMA-induced T cell activation pathway and therefore shall be a useful tool for understanding the roles of the 4F2 molecular complex.