• Cord blood inducer of suppressor T cell factor (TisF);
  • phenotype of inducer of suppressor T cells

ABSTRACT: Previously, we reported an antigen nonspecific inducer of T suppressor cell factor (TisF) produced by cord blood mononuclear cells (MNC) in 48-hr, two-way mixed lymphocyte cultures (MLC). The target of this factor was a radiosensitive, T4+ (T8) adult suppressor T cell subset. The cellular origin of this TisF was examined in the present study. IgG production by pokeweed mitogen (PWM)-stimulated adult MNC was used as an assay for TisF activity. It was found that TisF-producing cells formed rosettes with sheep erythrocytes (E+) and were independent of adherent cells (AC) in the production of TisF. They were resistant to irradiation (2500 rads) and phenotypic characterization with T cell reactive monoclonal antibodies indicated that they resided in the T8 (T4+) population. Furthermore, both TQ1 and TQ1+ cells were required for the production of TisF activity and such activity could not be reconstituted by supernatants from TQ1 MLC and TQ1+ MLC. These results indicate that the production of TisF is dependent upon interactions between radioresistant E +, T8, TQ1 and radioresistant E +, T8, TQ1+ cells.