Serological and functional characterization of human T cell subsets.

Two different specific anti-human T cell sera were studied. One was raised against fetal thymocytes (anti-HTY) and the other against human cultured T cells (anti-CTC) grown in the presence of conditioned medium from phytohaemagglutinin-stimulated peripheral blood mononuclear leucocytes (PBL). These sera, after various absorptions, reacted in microcytotoxicity assays against T cells, but not with B and null cells in the peripheral blood of both normal donors and patients with non-T leukaemias. A clear distinction between the labelling density of T versus B cells was also documented with the fluorescence-activated cell-sorter (FACS) analyses. These two sera were further absorbed on T cells from different sources with the aim of obtaining reagents specific for T cell subsets. Two reagents resulting from these absorptions were found to react with subsets of T-PBL. (1) Anti-HTY, after absorption with cells of a T-chronic lymphocyte leukaemia (T-CLL) expressing receptors for the Fc portion of IgG, reacted with thymocytes, 40–50% of normal T-PBL and only with those T cells that were not inhibited by theophylline in their ability to rosette with sheep erythrocytes. When PBL were preincubated with the absorbed serum and complement, the remaining cells had markedly diminished lymphoproliferative responses to lectins and in mixed lymphocyte culture (MLC), but they still responded well to tetanus toxoid (t.tox.). (2) Anti-CTC, after absorption with the MOLT-4 cell line reacted with about 30% of T-PBL and with the majority of the T-CLL cells with Fc receptors, as documented by cytotoxicity and FACS analyses. When normal PBL were preincubated with this absorbed serum and complement, the remaining cells had enhanced lymphoproliferative responses to lectins and especially to t.tox. and in MLC. Thus, these antisera, obtained following some rather simple absorption steps, were able to divide human T cells into two major and distinct subpopulations.