Expression of CD1d2 on thymocytes is not sufficient for the development ofNK T cells in CD1d1-deficient mice

CD1 is an MHC class I-like molecule that has been conserved throughout mamm alian evolution, Unlike MHC class I molecules, CD1 can present unique nonpr otein antigens to T cells. The murine CD1 locus contains two highly homolog ous genes, CD1d1 and CD1d2. CD1d1 is essential for the development of a maj or subset of NEI T cells that promptly secrete IL-4 following activation. H owever, the function of CD1d2 has not pet been demonstrated. In the present study, we examined the expression of CD1d2 in CD1d1-deficient (CD1d1 degre es) mire with the anti-CD1 Ab 3H3. Unlike CD1d1, which is expressed by all lymphocytes, CD1d2 can be detected only on the surface of thymocytes. To de termine whether CD1d2 can select a unique subset of NK T cells, He compared the remnant population of NK T cells in CD1d1 degrees and CD1d1. CD1d2-dou ble deficient (CD1d1 degrees CD1d2 degrees) mice. No significant difference in the number of NK T cells and cytokine secretion capacity can be detecte d between CD1d1 degrees and CD1d1 degrees CD1d2 degrees mice, indicating th at CD1d2 cannot substitute for CD1d1 in NK T cell development. The inabilit y of CD1d2 to select NK T cells is not due to the structural constraints of CD1d2 since CD1d2-transfected cells fan be recognized by both NI; T cell h ybridomas and freshly. isolated NR T cells. Given the structural similariti es, it is possible that the low levels of surface expression and Limited ti ssue distribution of CD1d2, map prevent it from functioning in the selectio n and expansion of NK T cells.