Human herpesvirus-6 dysregulates monocyte-mediated anticryptococcal defences

In order to investigate the interplay occurring between pathogens in the course of double infections, an in vitro model was set up in which the monocytic cell line THP-1 was exposed to Cryptococcus neoformans (Cn) and human herpesvirus 6 (HHV-6). Cn and HHV-6, both highly neurotropic, can cause serious diseases of the central nervous system and have monocytes, among other cell types, as target cells, causing alteration of their secretion pattern. Here, it was shown that unlike THP-1 cells exposed to cell-free virus inocula, THP-1 exposed to HHV-6-producing lymphocytes exhibited augmented phagocytosis against Cn. The phenomenon occurred after 24 h of monocyte/lymphocyte co-culture and was independent of direct cell-to-cell contact. Moreover, in the presence of HHV-6, THP-1 cells expressed enhanced secretory responses but reduced capability to counteract fungal infection: the enhanced ingestion by monocytes was followed by facilitated fungal survival and replication. These data provide initial in vitro evidence that HHV-6 may dysregulate monocyte-mediated anticryptococcal defences with an overall pro-cryptococcus result.