S-100 protein positive human T-lymphocyte.

S-100 protein was detected in a small number of human peripheral T-lymphocytes by a direct immunoperoxidase method with the use of monospecific antibody to S-100 protein. Complemented-mediated lysis using monoclonal antibodies revealed that the S-100+ T-lymphocytes bore OKT3, OKT8, and OKT11 antigens but not OKT4, OKM1, HLA-DR, HNK1 (Leu-7) antigens on their surface. Immunoelectron micrography showed that S-100 T-lymphocytes were small lymphocytes with poorly developed cellular organelles. These findings clearly indicated that S-100+ T-lymphocytes belonged to the OKT8+ T-cell subset, the so-called suppressor/cytotoxic T-cell subset. Although the function of the S-100+ T-lymphocytes is unclear, S-100 protein may be a useful cytoplasmic marker for the subdivision of the heterogeneous OKT8+ lymphocyte population.