The effect of a human plasma thymic factor on human peripheral blood mononuclear cell subpopulations

Human plasma thymic factor in vitro (human "facteur thymique sérique," or FTS) (at concentrations between 0.25 and 0.25 X 10(5) pg/ml) significantly increased "avid" E-rosette formation by human peripheral blood mononuclear cells (PBMC). It also increased the percentage of OKT8+ cells but did not affect the percentages of OKT3+, OKT4+, OKT11+, OKIa1+, or OKM+ cells. In the low-density immature PBMC, FTS increased both total and avid E-rosette formation, while increasing the percentages of OKT3+ and OKT8+ cells and decreasing the percentage of OKT4+ cells. Theophylline decreased E-rosette formation and the percentages of OKT3+ and OKT4+ among PBMC, and increased the percentages of OKT3+ and OKT4+ among the low-density cells. Human FTS may be capable of inducing maturation of immature PBMC into E-rosette-forming OKT3+8+ cells, while increasing the percentage of mature cells which may be doubly labeled OKT4+8+. The function of such doubly labeled cells remains to be determined. Human FTS may act by increasing intracellular cAMP in immature cells, but probably has a different mode of action in mature cells.