HLA-DO promotes bacterial superantigen binding to MHC class II molecules (106.27)

Abstract

Abstract HLA-DO (H2-O in mice) is an intracellular non-classical MHC class II molecule. It forms a stable complex with HLA-DM (H2-M in mice) and by regulating its activity shapes the peptide repertoire. Using a stable cell line overexpressing HLA-DO (HeLa-CIITA-DO), we show here that HLA-DO improved binding of SEA and TSST-1 superantigens (SAgs) to MHC class II molecules. Binding of SEB was not affected in these conditions. Exogenous pulsing of Class II-associated invariant chain peptide (CLIP) elucidate that CLIP is a major player in this process. Accordingly, HLA-DO knock-down using specific siRNA, decreased SEA and TSST-1 binding in HeLa-CIITA-DO cells. Furthermore, silencing of DM increased SEA and TSST-1 binding in HeLa-CIITA and 293-CIITA cells. Shutting down of Ii reversely decreased binding of SEA and TSST-1 in 293-CIITA cells. However, in HeLa-CIITA, Ii depletion just decreased SEA binding but does not affect TSST-1 binding. H2-O did not show the same boosting effect on SAgs binding in splenocytes. In conclusion, our results show that HLA-DO can improve SEA and TSST-1 binding in line with a role for CLIP in SAgs binding.