Mitogenic response of T-cell subclasses to agarose-linked and to free ribonucleotides

Thymocytes incubated with either ATP or GTP exhibit a brief period of enhanced DNA synthesis in contrast to the prolonged period of enhanced synthesis observed when thymocytes were incubated with concanavalin A. The cells responding to nucleotides represent a sub-population of theta antigen-bearing T cells comprising approximately 2% of the total thymocyte population as judged by a combined immunofluorescent/autoradiographic analysis. Thymocytes responsive to ATP and GTP are sensitive to cortisone suggesting that they are relatively immature T cells. ATP-responsive cells also preferentially aggregate with immature T cells when incubated with peanut agglutinin. GTP-responsive cells, on the other hand, do not. Nucleotides rendered insoluble by linkage to agarose via the ribose moiety are more active mitogenically at lower concentrations than either soluble nucleotides or even nucleotides linked to agarose via the nucleic acid base. The results are consistent with the view that the mitogenic response of thymocytes to nucleotides may be limited to as little as a single round of DNA synthesis and that such mitogenesis is stimulated at a site located on the plasma membrane.