Changes occurring on the surface of mouse T cells during concanavalin A-induced lymphoblastic transformation.

Thy-1 antigen and GPCA—the mouse T-cell surface component responsible for activation of guinea-pig complement (C)—were readily demonstrated on unstimulated but not on Con A-stimulated thymus or spleen cells when (guinea-pig) C-dependent cytotoxic reactions were used. Mitogenic stimulation was a necessary condition for these changes to occur since mere incubation of thymocytes in the absence of Con A failed to alter the sensitivity of these cells to treatment with either anti-Thy-1.2 antibodies plus C (devoid of non-specific cytotoxicity) or untreated guinea-pig serum (GPS) alone. Both Thy-1.2 and GPCA were, however, readily detectable on the Con A blasts when tested for by indirect immunofluorescence and immune adherence, respectively, i.e. by using tests which do not involve C-effected lysis. That Thy-1 was indeed expressed on the T-cell blasts was further indicated by their capacity to absorb anti-Thy-1.2 activity from specific antiserum. Con A, whether bound to the cells or added in excess to the reaction mixture, did not interfere with C-mediated lysis and was ruled out as a possible C inactivator. Pre-treatment of the lymphoblasts with neuraminidase rendered these cells sensitive to lysis by either anti-Thy-1.2 plus C or GPS. These results, highlighting altered reactivity of mouse T lymphoblasts with guinea-pig C, indicated the occurrence of surface changes during mitogen-induced blasto-genesis and suggested a role for sialic acid residues in interference with C-dependent cytotoxicity.