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Impaired NK cell development and enhanced NK cell mediated resistance to MCMV in NKG2D k.o. mice

NKG2D is a dominant activating receptor implicated in controlling both the innate and adaptive immune response. In mice, it is expressed on NK, NKT and T (activated and memory CD8+    and some   ) cells. NKG2D is a transmembrane type II glycoprotein, encoded by gene situated within the NK complex on the mouse chromosome 6. Cellular ligands for the NKG2D receptor in mouse (MULT-1, H60 and RAE-1 family) are poorly expressed on normal cells but can be induced upon infection or stress on wide variety of cell types. The role of NKG2D has been demonstrated in different models including the control of viral infections, tumors and autoimmunity. However, to address more specific questions on the role of NKG2D in the development, homeostasis and effector functions of the immune system the use of genetic approach seems to be preferable. We have generated NKG2D knock out mouse strain by targeting the NKG2D locus in Bruce 4 (C57BL/6) embryonic stem (ES) cells. Following the selection and screening procedure, we have identified 9 ES cell clones positive for the homologous recombination and negative for the random integration of the targeting vector. Upon the microinjection of the clones into CB20 blastocysts we have obtained several chimeras that have given germ-line transmission of the mutation. The flow cytometric analysis of CD8+ T and NK cells isolated from homozygous mice revealed complete absence of the NKG2D receptor, while its level was reduced in heterozygous mice as compared to the C57BL6 control. No major abnormalities either in the T cell development or in the distribution of mature T cell subpopulations were observed in mice homozygous for the NKG2D mutation. However, the analysis of NK cells in these mice revealed impaired NK cell development. Several phenotypical changes in the compartment of NK cell progenitors as well as in the pool of mature NK cells were detected. NK cell populations expressing c-kit and Ly49A were reduced, while the percentage of KLRG1+ NK cells was augmented. Furthermore, NK cells isolated from the spleen of homozygous mice were significantly less responsive to the NKG2D sensitive tumor targets than those from the control C57BL6 mice. Unexpectedly, however, NKG2D k.o. mice demonstrated the enhanced resistance to MCMV infection. This MCMV resistant phenotype was NK cell-dependent but independent of the Ly49H/m157 interaction.

NKG2D; k.o. mice; MCMV

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