Helper cell function of primed T cells. II. T‐T cell Synergism between Ig+ and Ig− subpopulations of primed thymocytes: a mechanism for amplification of helper cell function

AbstractThymocytes collected from spleens of lethally irradiated and thymocyte‐reconstituted mice, 6 h after “education” with SRBC, exert a markedly augmented helper cell function, especially for the 7 S response. Pretreatment of primed thymocytes with a rabbit anti‐mouse Ig serum and complement abolished the augmented helper cell function, although it had no effect on unprimed cells. Treatment of 6 h primed T cells with an anti‐Θ serum and complement also abolished the augmented helper cell function. However, in striking contrast with unprimed T cells where such treatment entirely abolished the helper cell function, the anti‐Θ treated 6 h T cells are still able to provide a significant helper cell function of the same magnitude as untreated nonprimed cells. This result suggests that a T cell subpopulation 6 h after priming becomes resistant to lysis by anti‐Θ serum and supports a substantial helper cell function. Since the sum of plaque‐forming cells (PFC) given by anti‐Ig and anti‐Θ‐treated 6 h primed cells was far smaller than the PFC given by untreated cells, a T‐T synergism is implicated as a mechanism for the augmented helper cell function of 6 h primed thymocytes.The amplification was also eliminated following treatment with a mouse anti SRBC serum indicating that some primed cells carry antigen on their surface. The data from various recombinations of primed cells treated with one of these three antisera, as well as primed cells treated sequentially with various combinations of two of the three antisera, suggested that the Ig+ and antigen‐carrying cells belong to the same subpopulation which is resistant to lysis by anti‐Θ serum. These cells are distinct from the rest which remain Ig− and still sensitive to lysis by anti‐Θ serum (Θ+).The Ig and antigen most likely represent a cytophilic complex present on the surface of a subpopulation of T cells. Thymocytes collected 5 days after education show little or no synergistic effect.The T‐T cell synergism described here may represent a basic regulatory function of T cells.