Thymus-dependent modulation of Ly49 inhibitory receptor expression on NK1.1+γ/δ T cells.

Summary Major histocompatibility complex (MHC) class I-specific inhibitory receptors are expressed not only on natural killer (NK) cells but also on some subsets of T cells. We here show Ly49 expression on γ/δ T cells in the thymus and liver of β₂-microglobulin-deficient (β₂m^-/-) and C57BL/6 (β₂m^+/+) mice. Ly49C/I or Ly49A receptor was expressed on NK1.1⁺γ/δ T cells but not on NK1.1^-γ/δ T cells. The numbers of NK1.1⁺γ/δ T cells were significantly smaller in β₂m^+/+ mice than in β₂m^-/- mice with the same H-2^b genetic background. Among NK1.1⁺γ/δ T cells, the proportions of Ly49C/I⁺ cells but not of Ly49A⁺ cells, were decreased in β₂m^+/+ mice, suggesting that cognate interaction between Ly49C/I and H-2K^b is involved in the reduction of the number of Ly49C/I⁺ γ/δ T cells in β₂m^+/+ mice. The frequency of Ly49C/I⁺ cells in NK1.1⁺γ/δ T cells was lower in both lethally irradiated β₂m^+/+ mice transplanted with bone marrow (BM) from β₂m^-/- mice and lethally irradiated β₂m^-/- mice transplanted with BM from β₂m^+/+ mice than those in adult thymectomized BM-transplanted chimera mice. These results suggest that reduction of Ly49C/I⁺ NK1.1⁺γ/δ T cells in β₂m^+/+ mice is at least partly due to the down-modulation by MHC class I molecules on BM-derived haematopoietic cells or radioresistant cells in the thymus. [ABSTRACT FROM AUTHOR]