Murine fetal natural killer cells are functionally and structurally distinct from adult natural killer cells

Natural killer (NK) cell phenotype and activity was studied by analyzing un cultured and short-time-cultured murine NK cells from fetal day 17 spleen a nd thymus, In contrast to NK cells from adult mice, freshly sorted fetal NK cells did not contain NK receptor transcripts for Ly-49A, B, C/I, D, F, G2 , or H. The only NE receptor transcripts that could be detected were Ly-49E and CD94.. It is important that Ly-49E was present at a 10- to 30-fold hig her level compared with uncultured NK cells from adult mice, After short-ti me interleukin-2 culture, the level of Ly-49E mRNA was comparable between f etal and adult Nh cells, Functionally, fetal Ng cells only killed MHC class I-negative tumor cells when activating NIC receptors were cross-linked wit h antibody. We show that fetal NK cells are mature but are different from N h cells in adult mice regarding their NE cell receptor repertoire and funct ion.