S100A9 and HIV-1 infection: Though neither Nef nor Vpu proteins, both of which are able to down regulate HLA class-I molecules [30,31], seemed to be implicated in these S100A8 and S100A9 expression modulations on MDDC in response to HIV-1 infection (Additional file 5: Figure S5 and data not shown), however, we cannot rule out an implication of other HIV-1 proteins.