This paper explores the ontogeny of NK cells in control and early-thymectomized (Tx) @entity1238 through phenotypic analysis of cells expressing the NK cell antigen 1F8 and by performing in vitro cytotoxic assays. Dual color flow cytometry reveals that a few 1F8positive splenocytes first emerge in late larval life, at approximately 7-weeks post-fertilization. This is about 2-weeks after the time when surface MHC class Ia expression can first be detected. The proportion of splenocytes expressing 1F8 remains very low in 3-4 month-old froglets, but by 1 year there is a sizeable 1F8positive population, which is proportionally elevated in Tx frogs. The ontogeny of NK cell function is monitored by a 5 h DNA fragmentation (JAM) assay. Control and Tx larval splenocytes (from either 5- or 7-week-old tadpoles) fail to kill MHC-deficient thymus-derived @entity5 cell targets. Such in vitro killing is still relatively poor in 3-4 month froglets, compared with high levels of @entity5 cell @entity137 mediated by splenocytes from older frogs. Immunoprecipitation studies identify that the major ligand for the 1F8 mAb is a 55 kDa polypeptide. Finally, further evidence is provided that 1F8positive lymphocytes are indeed bona fide NK cells, distinct from T cells, since purified 1F8positive splenocytes from Tx @entity1238 fail to express fully rearranged @entity70344 V region transcripts. We conclude that NK cells fail to develop prior to MHC class I protein expression and, therefore, do not contribute to the larval immune system, whereas they do provide an important backup for T cells in the adult frog by contributing to anti- @entity5 immunity.

Ontogeny of XXXX NK cells in the absence of MHC class I antigens.

@entity5 :: ('MESH:D009369', 'Disease') :: ['tumor'] @entity137 :: ('MESH:D064420', 'Disease') :: ['cytotoxicity'] @entity1238 :: ('8355', 'Species') :: ['Xenopus laevis', 'Xenopus'] @entity70344 :: ('378564(Tax:8355)', 'Gene') :: ['TCRbeta']
@entity1238 :: (8355,Species) :: ['Xenopus']
