Natural killer lymphocytes: "null cells" no more.
Natural Killer (NK) lymphocytes were initially described as potent effector cells that, unlike T lymphocytes, were able to kill targets in the absence of a priori stimulation and without specific recognition mechanisms. Over the past ten years however, it has been clearly demonstrated that NK cell function is regulated by a number of surface receptors that bind specific ligands expressed by target cells. Some of these receptors display inhibitory functions and recognize MHC class I molecules expressed by normal autologous cells that, as a consequence, are spared from indiscriminate NK-mediated killing. Other receptors are involved in NK cell activation against allogeneic cells or cells that, upon viral infection or tumor transformation, down-regulate MHC Class I expression. Altogether these data provide important advances toward the understanding of the complexity of the molecular mechanisms that regulate NK-mediated functions.
Moretta
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Dipartimento di Medicina Sperimentale, Sezione di Istologia, Università di Genova, Italy. alemoret@unige.it
Bottino
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C
Sivori
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S
Marcenaro
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E
Castriconi
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R
Della Chiesa
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M
Carlomagno
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S
Augugliaro
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R
Nanni
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Vitale
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Millo
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R
D003602:Cytotoxicity, Immunologic; D006801:Humans; D007694:Killer Cells, Natural / Q000166:cytology / Q000276:immunology*; D011971:Receptors, Immunologic / Q000276:immunology
D011971:Receptors, Immunologic