Response of mammalian macrophages to challenge with the Chlorovirus ATCV-1.

Petro TM1, Agarkova IV2, Zhou Y3, Yolken RH4, Van Etten JL2, Dunigan DD5.

It was recently reported that 44% of healthy humans in a study cohort had DNA sequences similar to Chlorovirus ATCV-1 (family Phycodnaviridae) in oropharyngeal samples and had decreases in visual processing and visual motor speed compared with individuals in whom no virus was detected. Moreover, mice inoculated orally with ATCV-1 developed immune responses to ATCV-1 proteins and had decreases in certain cognitive domains. Because heightened IL-6, nitric oxide (NO), and ERK MAP-kinase activation from macrophages are linked to cognitive impairments, we evaluated cellular responses and viral plaque forming units in murine RAW264.7 and primary macrophages after exposure to ATCV-1 in vitro for up to 72 h after virus challenge. Approximately 8% of the ATCV-1 inoculum was associated with macrophages after 1 h and increased 2-3 fold over 72 h. Immunoblots using rabbit anti-ATCV-1 detected a 55 kDa protein consistent with viral capsid protein from 1 to 72 h and an increasing de novo synthesis of a previously unidentified 17 kDa protein beginning at 24 h. Emergence of the 17 kDa protein did not occur and persistence of the 55 kDa protein declined over time when cells were exposed to heat-inactivated ATCV-1. Moreover, starting at 24 h, RAW264.7 cells exhibited cytopathic effects, Annexin V staining and cleaved-caspase 3. Activation of ERK MAP-kinases occurred in these cells by 30 min post challenge, which preceded expression of IL-6 and NO. Therefore ATCV-1 persistence in and induction of inflammatory factors by these macrophages may contribute to declines in cognitive abilities of mice and humans.