Flow cytometry analysis of NKR expression on CD3⁻CD56⁺ NK cells. (A) The size of NKR⁺ NK-cell subsets expressing NKp30, NKp46, CD161, NKG2A and NKG2C, CD69, and CD85j were evaluated after gating of positive CD3⁻CD56⁺ NK cells in exposed HIV-infected IDU (HIV, ▴), exposed HIV-uninfected IDU (EU, •), and unexposed control blood donors (C, □, Horizontal bars represent the median and the 25th-75th percentiles. NKp30 and NKp46 were expressed on all NK cells (100% CD3⁻CD56⁺), and comparison of expression levels where thus analyzed by analysis of mean fluorescence intensity (mfi). NK-cell surface expression of NKG2A inhibitory subunit of the CD94/NKG2A heterodimeric receptor was inversely correlated to that of the stimulatory NKG2C subunit among CD3⁻CD56⁺ NK cells in EU subjects (Spearman correlation test), whereas correlation was nonsignificant in C and HIV groups. (B) Representative flow cytometer analyses of NKR staining in exposed HIV-infected IDU (HIV), exposed uninfected IDU (EU) and unexposed controls (C) (white: isotypic control staining; black, NKR specific staining).