Activation-dependent Expression of Low Affinity IgG Receptors Fc Gamma RII(CD32) and Fc Gamma RIII(CD16) in Subpopulations of Human T Lymphocytes

Receptors for IgG (Fc gamma R) are expressed by small subpopulations of peripheral blood T lymphocytes. Our studies demonstrate that T lymphocytes can be induced in vitro to express two different low-affinity Fc gamma R. Mitogen activation of peripheral blood T lymphocytes obtained from eight healthy individuals leads to considerable augmentation of the Fc gamma RIII+ (CD32) T cell subpopulation. The highest percentage of CD32 expressing T lymphocytes could be detected after three days of activation. The T cell subpopulation which transiently express the CD32 antigen, encompasses CD4+ and CD8+ cells. Molecular cloning of the CD32 antigen by reverse transcription and polymerase chain reaction demonstrates that activated human T lymphocytes express the Fc gamma RIIIb2 isoform. The percentage of the Fc gamma RIII+ (CD16) T cell subpopulation was significantly increased only in the lymphocyte populations obtained from three out of eight volunteers immediately after mitogen activation. However, during short-term cell culture the CD16 expressing CD8+ T cell subset increased in the T cell population from all individuals investigated. During this time, the IL-2 receptor alpha-chain (CD25) expression level decreased as a function of time. In contrast to the CD8+CD16+ T cells, the percentage of the non-MCH-restricted CD56+CD16+ T cells was not influenced by mitogen activation and time of cell cultivation. We could show that CD16 in T cells is able to mediate a stimulus leading to proliferation of the CD8+CD56-CD16+ T cells but not that of the CD56+CD16+ T cell subset. This discrepancy cannot be explained by the expression of different Fc gamma RIII isoforms, because both T cell subsets express Fc gamma RIIIA alpha, as we demonstrate in this report.