Abstract
HLA class I and II molecules play a central role in regulating host immune responses against microbial infections because they present foreign antigens to CD8+ and CD4+ T lymphocytes, respectively. Many cytokines, especially interferons (IFN), are known to upregulate human leucocyte antigen (HLA) class I and II gene expression, but the kinetics, expression levels and viral regulation of HLA genes in primary human cells have not been well documented. Stimulation of peripheral blood mononuclear cells (PBMC) with IFN-alpha and IFN-gamma resulted in a 1.5- to twofold increase in HLA class I and beta 2-microglobulin expression in lymphocytes and monocytes. Lymphocytes did not express any detectable HLA class II either basally or after IFN induction. In monocytes, instead, a high basal class II expression was found and it was further induced by IFN-alpha (up to twofold) and especially by IFN-gamma (up to fivefold). In granulocyte-macrophage colony-stimulating factor (GM-CSF) differentiated human macrophages, basal HLA class I and II protein expression levels were high but IFN-gamma stimulation was able to further enhance their expression. Accordingly, class I and II mRNA expression was elevated by IFN-gamma, whereas IFN-alpha practically had no effect on HLA class I mRNA levels. Influenza A virus infection of macrophages resulted in temporary increases in HLA class I, beta 2-microglobulin and class II antigen expression. Neutralization of virus-induced IFN production by antibodies against type I and II IFNs prevented the virus-induced upregulation of HLA antigens. At late times of infection, as analysed by steady-state mRNA expression, both HLA class I and II mRNA were strongly reduced. These results suggest that IFNs are important regulators of HLA genes and responsible for a temporary increase in HLA antigen expression during influenza A virus infection.