Differential contribution of the FcRγ chain to the surface expression of the T cell receptor among T cells localized in epithelia: analysis of FcRγ-deficient mice

The function of the Fc receptors γ chain (FcR_γ) for the expression of the T cell receptor (TCR) complex and for T cell development, especially for T cells localized in epithelia, was investigated by analyzing FcR_γ-deficient mice. In wildtype mice, CD8αα⁺β^?TCRαβ⁺ T cells of intestinal intraepithelial lymphocytes (i-IEL) utilized CD3ζ homodimers and ζ-FcR_γ heterodimers, whereas CD8α α⁺β^?TCR_γδ⁺ i-IEL used ζ-FcR_γ and FcR_γ homodimers in the TCR complex. On the other hand, these T cells in FcR_γ-deficient mice contained only ζ homodimers. The surface expression of the TCR complex was reduced in CD8αα⁺β^?i-IEL and dendritic epidermal T cells (DETC) in these mice, whereas the development of these T cells was normal. The degree of reduction appeared to depend on the expression level of FcR_γ. In contrast to these populations, TCR_γδ⁺ intraepithelial T cells in reproductive organs (r-IEL) were dramatically decreased, suggesting that the development of r-IEL is FcR_γ-dependent, probably due to the predominant usage of FcR_γ homodimers in the TCR complex. These results indicate that the FcR_γ chain contributes differently to the TCR expression and to the development of T cells localized in epithelia.