It has been suggested that NK cells may contribute to immunopathology during chronic hepatitis 20, 32. Both HBV and HCV appear to be involved in the modulation of HLA-E,

the ligand of NKG2C, suggesting that NKG2C+ NK cells might target HLA-E expressing hepatocytes in the liver. Intriguingly, despite their cytolytic potential, we found no correlation between expansion of polyfunctional NKG2C+ CD56dim NK cells and clinical parameters including viral load and alanine transaminase (ALT) levels (Supporting Information 4). KIR expression is a major Selleck CHIR 99021 event in the terminal differentiation of NK cells 10, 11. Figure 3A shows the KIR expression profile of NKG2C+ and NKG2C− CD56dim NK cells in representative patients. In each patient, a fraction of the NKG2C−CD56dim subset expressed KIR2DL1, KIR2DL2/DL3, KIR3DL1, and/or KIR2DS4 in agreement with a variegated distribution of KIRs. In contrast, NKG2C+CD56dim cells had a more restricted KIR expression pattern with a dominant expression of one or two inhibitory KIRs (Fig. 3A). For example, NKG2C+CD56dim cells from patient 2 exclusively expressed KIR2DL2/3, whereas those of patient 16 expressed mainly KIR3DL1. For still other patients, oligoclonal expression of KIR2DL1 and KIR2DL2/DL3 dominated the NKG2C+ NK cells, as exemplified for patient 3. KIR2DL2/DL3

was the most frequently expressed KIR (87% of donors) compared with KIR2DL1 (35%) and KIR3DL1 (30%), in NKG2C+ NK cells (Fig. Ridaforolimus 3B and Table 2). More importantly, the KIR expressed on NKG2C+CD56dim NK cells was in most cases specific for self-HLA class-I ligands (Table 2). Hence, KIR2DL1 and KIR2DL2/DL3 were significantly more expressed in the

presence of two alleles of their respective ligands, HLA-C group 2 (HLA-C2) and group 1 (HLA-C1) (Fig. 3C and D). Further, KIR3DL1 expression in NKG2C+ NK cells was almost exclusively observed in donors displaying the cognate ligand, HLA-B group Bw4 (HLA-Bw4) (Fig. 3E). Intriguingly, three donors (4, 13 and 21) had NKG2C+ NK cells expressing KIR2DL2/DL3, although they were homozygous for HLA-C2 alleles. It is known, Dipeptidyl peptidase however, that KIR2DL2 has a low affinity for HLA-C2 33, 34. KIR genotyping of patients 4, 13, and 21 showed that all possessed the KIR2DL2 gene, suggesting that these too had dominant expression of self-specific receptors (Supporting Information 5). HLA-A typing for patient 16, who expressed KIR3DL1, but had no HLA-Bw4 alleles, showed an HLA-A*24 allele, which is also a ligand for KIR3DL1 34, 35. Taken together, these results unambiguously showed that clonally expanded NKG2C+CD56dim NK cells expressed a KIR that specifically recognized self-HLA class-I molecules. Next, we examined the functional role of clonal KIR expression in the expanded NKG2C+ NK cells.