Biological specificity of low molecular weight inhibitors of lymphocyte transformation

Extracts of calf thymus have been shown to contain a number of inhibitors of lymphocyte transformation. A low molecular weight (600 daltons) anionic inhibitor of lymphocyte transformation has been identified and separated from contaminating polyamines and nucleotides. The active fraction inhibited the DNA synthetic response of murine or human T cells to alloantigens in mixed lymphocyte culture and to T-cell-specific mitogens. It was inactive against stimulation of B lymphocytes and several cultured tumor cell lines.