Herpes Simplex Virus (HSV) types 1 and 2 are among the most common human viral pathogens and are capable of causing serious disease, including fatal disseminated neonatal herpes, herpes simplex encephalitis, genital herpes, and blinding herpes keratitis. There is no effective HSV vaccine currently available, there are many live-attenuated, inactivated, and replication defective HSV vaccine approaches currently in development. However, HSV entry into dendritic cells (DCs) is incompletely understood, much less the highly complex process of cross-presentation. Currently it is known that HSV utilizes at least three different entry pathways to infect different cell types, a pH-dependent endocytic pathway, a pH-independent endocytic pathway and a pH independent fusion pathway at the plasma membrane. Using inhibitors of endosomal acidification, bafilomycin A and monensin, and the protein tyrosine kinase inhibitor genistein, flow cytometry and PCR were used to measure infection, we showed that HSV1 and HSV2 enters human monocyte-derived DCs via a pH-dependent endocytic pathway. Presentation of UV-inactivated HSV1 to CD4 T cells from HSV seropositive donors, measured by interferon gamma ELISPOT, was inhibited by bafilomycin A but cross-presentation to CD8 T cells was enhanced by bafilomycin A and blocked by the proteasomal inhibitor lactacystin. Therefore although both HSV infection and cross-presentation occur via endosomal uptake, subsequent pathways differ. Further understanding of the mechanisms of infection and cross-presentation of HSV should lead to better vaccine design.
Funding: NHMRC