Relative expression levels of the HLA class-I proteins in normal and HIV-infected cells

摘要

The expression level of human leukocyte antigens (HLA) is known to influence pathological outcomes: pathogens downregulate HLA to evade host immune responses, host inflammatory reactions upregulate HLA, and differences between people in steady-state expression levels of HLA associate with disease susceptibility. Yet precise quantification of relative expression levels of the various HLA loci is difficult due to the tremendous polymorphism of HLA. We report relative expression levels of HLA-A, HLA-B, HLA-C and HLA-E proteins for the specific haplotype A*02:01, B*44:02, C*05:01, characterized using two independent methods based on flow cytometry and mass spectrometry. Peripheral blood lymphocytes from normal donors showed that HLA-A and HLA-B proteins are expressed at similar levels, which are 13-18 times higher than HLA-C by flow cytometry and 4-5 times higher than HLA-C by mass spectrometry, differences that may reflect variation in the conformation or location of proteins detected. HLA-E was detected at a level 25 times lower than that of HLA-C by mass spectrometry. Primary CD4+ T cells infected with HIV in vitro were also studied since HIV downregulates selective HLA types. HLA-A and -B were reduced on HIV-infected cells by a magnitude that varied between cells in an infected culture. Averaging all infected cells from an individual showed HLA-A to be 1-3 and HLA-B to be 2-5 times higher than HLA-C for different individuals by flow cytometry. These results quantify substantial differences in expression levels of the proteins from different HLA loci, which are very likely physiologically significant on both uninfected and HIV-infected cells.