Surface phenotype of responder cells in the syngeneic mixed lymphocyte reaction in mice

The organ distribution and surface phenotype of SMLR responder cells has been investigated. Nylon-wool-passed spleen cells, which proliferate in response to mitomycin-C-treated syngeneic spleen cells, are Thy 1.2⁺ Ly 1⁺2^?3^?. SMLR responder cells are not confined to the spleen since nylon-wool-nonadherent lymph node cells as well as unfractionated thoracic duct lymphocytes show activity. Responder cells have characteristics of mature T cells since cortisone-resistant thymocytes, but not thymocytes from untreated mice, are capable of SMLR response. In addition, naturally occurring thymocytotoxic antibody (NTA), which in our experiments exhibits cytotoxicity only for thymocytes, does not appear to affect the subpopulation of the T cells which respond in the SMLR.