Regulation of NKT Cells by Ly49: Analysis of Primary NKT Cells and Generation of NKT Cell Line

摘要

TCR#alpha##beta#~+NK1.1~+ (NKT) cells are known to express various NK cell-associated molecules including the Ly49 family of receptors for MHC class I, but its functional significance has been unclear. Here, we examined the expression of Ly49A, C/I and G2 on various NKT cell populations from normal and MHC class I-deficient C57BL/6 mice as well as their responsiveness to #alpha#-galactosylceramide (#alpha#-GalCer), a potent stimulator of CD1d-restricted NKT cells. The frequency and the level of Ly49 expression varied among NKT cells from different tissues, and were regulated by the expression of MHC class I and CD1d in the host. Stimulation of various NKT cells with #alpha#-GalCer suggested that Ly49 expression inversely correlated with the responsiveness of NKT cells to #alpha#-GalCer. Moreover, #alpha#-GalCer presented by normal dendritic cells stimulated purified Ly49~-, but not Ly49~+, splenic NKT cells, whiereas NHC class I-deficient dendritic cells presented #alpha#-GalCer to both Ly49~+ and Ly49~- NKT cells equally well. Therefore, MHC class I on APCs seems to inhibit activation of NKT cells expressing Ly49. To further characterize CD1d-restricted NKT cells we generated an #alpha#-GalCer-responsive NKT cell line from thymocytes. The line could only be generated from Ly49~-NK1.1~+CD4~+ thymocytes but not from other NKT cell subsets, and it lost expression NK1.1 and CD4 during culture. Together, these results indicate the functional significance of Ly49 expression on NKT cells.