Enhanced cAMP production by activated human Fc-IgG receptor positive T-cell subpopulations

Abstract

Human peripheral T lymphocytes were separated into subpopulations on the basis of Fc-receptor expression or on the basis of their ability to rerosette with sheep red blood cells (SRBC) after incubation with theophylline. The baseline levels of cAMP in the Fc-receptor-positive and -negative subpopulations and in the theophylline-sensitive and -resistant subpopulations were equally low. However, within 5–30 min after stimulation with PGE 2 and theophylline, both the Fc-IgG receptor-positive T-cell subpopulation (T G) and the theophylline-sensitive T-cell subpopulation (T TS) showed greatly enhanced cAMP levels. Isoproterenol and theophylline also enhanced cAMP levels of the T G subpopulation more than in the T-non G subpopulation. In addition the T-non M subpopulation had higher stimulated cAMP levels than the T M subpopulation in the absence of Fc-IgG receptor interaction. This suggests that the Fc-IgG receptor-positive T cells are more responsive to stimulation of cAMP levels than the Fc-IgM receptor-positive subpopulation. However, since cAMP levels in T cells incubated with IgG-immune complexes were significantly higher than T cells incubated with IgM-immune complexes, the enhanced cAMP response of the T G subset can be attributed in part to a stimulating effect of Fc-IgG receptor interaction. Since the T G subpopulation and the T TS subpopulation have a greater capacity to produce cAMP, we hypothesize that cAMP may be involved in mediating the functionally distinctive properties of these human T-cell subpopulations.