In vivo differentiation of cytotoxic T lymphocytes. 1. Serum factor in immunized athymic (nu/nu) mice could differentiate CTL precursor.

Mature cytotoxic T lymphocytes (CTLs) were hardly detected by 51Cr-release assay in the spleen of C3H/He mice after an intravenous injection of spleen cells of C57BL/6 (B6) mice. B6-specific CTL generation was augmented by transfer of sera obtained from C3H/He mice inoculated subcutaneously with EL-4 cells of B6 origin, P815 cells of DBA/2 origin or MH134 cells of C3H/HeN origin or these injected intraperitoneally with sheep or chicken erythrocytes. Such a factor can be produced also by athymic (nu/nu) mice. Such an augmentation of cytotoxicity was detected also in the regional lymph nodes after subcutaneous injection of allogeneic spleen cells. This factor may be different from augmenting factors reported already.