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-2b 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-2Kb 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]