Herpes simplex virus type I infection of mature dendritic cells leads to reduced LMP7-mRNA-expression levels.

Mature dendritic cells (mDCs) are the most potent antigen presenting cells within the human immune system known today. However, several viruses, including herpes simplex virus type 1 (HSV-1) have developed numerous immune escape mechanisms, such as the avoidance of peptide presentation through the major histocompatibility complex (MHC) class I to CD8(+) cytotoxic T-cells. Within the MHC class I pathway, the majority of antigenic peptides are generated by the proteasome, a multicatalytic protease complex. Upon exposure to IFN-gamma, the constitutive proteasome is partially replaced by the immunoproteasome, which contains the IFN-gamma-inducible subunits LMP2, MECL1 and LMP7. In this study, we report the downregulation of LMP7 on mRNA level in HSV-1 infected mDCs. Interestingly, this reduction was not vhs-mediated since using a virus strain lacking the vhs gene we obtained similar results. However, on protein level, LMP7-expression was not affected, which is probably due the high stability of the LMP7 protein. Also the incorporation of LMP7 into the immunoproteasome was not affected by HSV-1. However, for the in vivo situation, in which DC reside for a prolonged time period in peripheral tissues, the reduced LMP7-mRNA level could be of biological importance, since the virus could escape/hide from immune system of the host and establish latency processes.