LAUSR

Aim The established variability of HLA-C expression on cell surface, although already investigated in African Americans by Apps et al. Science 2013(1), has not been yet accordingly researched in Caucasians. Furthermore, the possibility that HLA-C expression heterogeneity may be attributed to an overall HLA-Class I expression regulation has not been thus far experimentally addressed either. This work aims at elucidating both issues through actual protein expression analysis by flow-cytometry in 188 German healthy blood donors. Methods 188 buffy-coats provided from the Ulm Blood Donor Centre were used for leucocyte collection in order to determine by flow cytometry the protein expression levels of HLA-C and HLA-Class I on lymphocytes as previously described 1 . For HLA-C and HLA-Class I expression estimation, a DT-9 and an anti-HLA-ABC Antibody were used. Median Intensity Fluorescence (MFI) coefficients were calculated for each HLA-C allotype through implementation of a linear regression model. Results According to our findings, HLA-C03, -C07 and -C08 (MFI: 408, 450 and 481 respectively) were ranked as low-expressed HLA-C antigens contrary to HLA -C12, -C14 and -C01, which were notably higher expressed (MFI: 1261, 1280 and 1322 respectively). In addition, our data on overall HLA-Class I expression levels were suggestive of no direct correlation between HLA-C and HLA-Class I expression levels on cells as: (1) The divergence range of expression levels for HLA-Class I was markedly narrower (MFIs: 450–758 vs 408–1322). (2) Low expressed HLA-C allotypes were found linked with high HLA-Class I expression levels (e.g. C08: 758 for HLA-Class I vs 481 for HLA-C). Conclusions Our HLA-C expression results match significantly those of Apps et al. at least with respect to high-and low-expressed HLA-C antigens, despite the different race of subjects included in the two studies. Moreover, of high interest is our finding regarding the lack of association between HLA-C and HLA-Class I expression, which in turn points to an HLA-C rather than an HLA-Class I specific expression- regulating factor accounting for this marked divergence in HLA-C expression levels. Further investigation on a much greater scale is nevertheless mandatory before final conclusions can be drawn.