Expression and function of Fc receptors in the thymus

In this review, the expression and function of Fc receptors (FcRs) in the thymus is discussed. In the murine thymus, Fc gamma RII and Fc gamma RIII are expressed on early thymocyte precursors, which can differentiate in both T and NK cells. TCR alpha beta thymocytes that are differentiating along the CD4-CD8 pathway do not express Fc gamma Rs any longer. Mature CD4-CD8 double negative TCR alpha beta and TCR V gamma 3 cells, however, constitutively express Fc gamma RII/III. The generation of gene-deficient mice has shown that neither Fc gamma Rs nor Fc epsilon RII are indispensable for murine thymus-dependent T cell development, whereas normal development of thymus-independent peripheral T cells is dependent on the presence of the FcR gamma chain. In the human thymus, a low number of CD3-CD4-CD8 triple negative cells expresses Fc gamma RIII, but these cells are mainly NK cells. Fc epsilon RII is expressed on human thymic epithelial cells. Although the unaltered thymic development of T cells in FcR-deficient mice argues against a fundamental role of FcRs in this process, recent demonstration of FcR ligands of non-immunoglobulin nature in the thymus indicates that the interaction between FcRs and their ligands in the thymus might influence T cell development.