Journal
DEVELOPMENTAL AND COMPARATIVE IMMUNOLOGY
Volume 27, Issue 8, Pages 715-726Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/S0145-305X(03)00040-5
Keywords
amphibians; NK cell ontogeny; NK cell-associated 1F8 antigen; Xenopus; thymectomy; tumor immunity
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Funding
- NCI NIH HHS [CA-76312] Funding Source: Medline
- NIAID NIH HHS [AI-44011] Funding Source: Medline
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This paper explores the ontogeny of NK cells in control and early-thymectomized (Tx) Xenopus laevis 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 similar to 7-weeks post-fertilization. This is about 2-weeks after the time when surface MHC class la 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 It DNA fragmentation (JAM) assay. Control and Tx larval splenocytes (from either 5- or 7-week-old tadpoles) fail to kill MHC-deficient thymus-derived tumor cell targets. Such in vitro killing is still relatively poor in 3-4 month froglets, compared with high levels of tumor cell cytotoxicity 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 Xenopus fail to express fully rearranged TCRP 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-tumor immunity. (C) 2003 Elsevier Science Ltd. All rights reserved.
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