Expression of Ly49E and CD94/NKG2 on fetal and adult NK cells

Murine NK cells express inhibitory receptors belonging to the Ly49 and CD94 /NKG2 family. Ly49E and CD94 are the only NK cell receptor transcripts dete ctable in fetal NK cells. Still unproved is the surface expression of Ly49E on NK cells. Here we generated two novel mAbs, a mAb recognizing Ly49E wit h cross-reactivity to Ly49C, and a mAb against NKG2A/C/E. Ly49E was immunop recipitated as a disulfide-linked homodimer with 46-kDa subunits. Removal o f N-linked carbohydrates revealed a 31-kDa protein backbone. NKG2A was immu noprecipitated as a 38-kDa protein. Although the frequency of fetal NK cell s expressing Ly49E was higher than 25%, it decreased drastically from 2 wk after birth. Phenotypic analysis showed that similar to 90% of fetal NK cel ls and similar to 50% of adult NK cells express high levels of CD94/NKG2. T he remaining 50% of adult NK cells expressed low surface levels of CD94/NKG 2. Expression of Ly49E and CD94/NKG2 was not restricted to NK cells, but wa s also observed on NK T and memory T cells. Functional analysis showed that sorted Ly49E(+) and CD94/NKG2(+) fetal NK cells could discriminate between MHC class I-positive and MHC class I-negative tumor cells. We also demonst rated that Ly49E becomes phosphorylated following pervanadate stimulation o f fetal NK cells. The expression levels of Ly49E and CD94/NKG2 were similar in wild-type compared with beta (2)-microglobulin(-/-) mice. In conclusion , generation of mAbs against Ly49E and NKG2 extended the phenotypic and fun ctional characterization of NK cells.