[OK T-positivity in stimulated T-lymphocytes]

T-lymphocytes express different antigenic determinants which can be recognized using specific anti-T monoclonal antibodies. OK T3 (Ortho Diagnostics, Raritan, N.J.) detects 95% circulating T-lymphocytes, while OK T4 reacts with helper/inducer T-lymphocytes and OK T8 with suppressor/cytotoxic T-lymphocytes. In normal peripheral blood the proportion of mononuclear cells (after "Lymphoprep' separation) positive with the various anti-T monoclonal antibodies is, according to our standards, as follows: OK T3 77 +/- 9.4%, OK T4 51 +/- 7.8%, OK T8 27+/- 6.4%. In this study we have evaluated the positivity with OK T MoAb after activation and proliferation of the T-cell population in a double layer T-lymphocyte colony assay. After 4-5 days of incubation, the proportion of OK T3 + cells had increased to 94 +/- 4.6%, while that of OK T4+ and OK T8+ had raised to 62 +/- 14.1% and 65 +/- 7.1% respectively. These data suggest that T-colony formation gives rise to an increased expression of OK T8 positivity, possibly through a mechanism of T-cell activation (shown also by the 'Ia' positivity), and/or of proliferation of T-cells with a double antigenic phenotype.