Activity and phenotype of natural killer cells in peptide transporter (TAP)-deficient patients (type I bare lymphocyte syndrome)

In this paper we describe the function and phenotype of natural killer (NK) lymphocytes from HLA class I-deficient patients. These cells are, as has been previously reported, unable to lyse HLA class I^- K562 cells, but are able to perform antibody-dependent cellular cytotoxicity (ADCC), although with lower efficiency as compared to NK cells from normal individuals. Transporter associated to antigen processing (TAP)^- NK cells proliferate when cultured in the presence of lymphoblastoid B cells (B-LCs) and interleukin 2 and develop a spectrum of cytotoxicity similar to that of activated normal NK cells. Importantly, activation of the TAP^- NK cells induces strong cytotoxicity to autologous B-LCs. Analysis of the phenotype of circulating TAP^- NK lymphocytes showed them to display a normal diverse repertoire of HLA class I-specific NK receptors. These receptors were expressed at normal levels, apart from the CD94-NKG2A complex, which appeared to be overexpressed. This latter finding could reflect an adaptation to the low expression of HLA class I molecules. Finally, functional analyses indicated that the inhibitory receptors in TAP^- individuals can transduce inhibitory signals. Our results suggest that in vivo, the NK cells of TAP^- patients could participate in immune defense, at least through ADCC, but upon activation, may be involved in autoimmune processes.