The role of CD40 in calcitonin gene related protein (CGRP) mediated antiviral effect in glial cells

Abstract

LP-BM5 is a murine retrovirus that induces peripheral neuropathy and AIDS like immune deficiency in B6 mice. Upon infection, primary sensory neurons in the spinal cord express elevated levels of calcitonin gene related protein (CGRP). Previously, we showed that CGRP induced reduction of LP-BM5 viral loads in primary mixed glial cells. The purpose of this current study was to investigate possible CGRP downstream targets that may contribute to its antiretroviral response. We hypothesized that CGRP decreases the viral load in glial cells by modifying the CD40 expression; increasing in CD40 signaling may promote production of cytokines and chemokines with antiretroviral properties. Using CD40 knockout mice we showed that CD40 is required for CGRP mediated antiretroviral response in mixed glia. In microglial cell line, CD40 expression was elevated after treatment with CGRP. Similar effect was seen in microglia from spinal cord derived mixed glial cultures. While LP-BM5 increased microglial CD40 expression gradually over time up to 7 days post-infection in primary mixed glia, CGRP caused an early elevation (24 hr post-infection) of microglial CD40 expression in microglia and stayed relatively steady levels 7 days after infection. CGRP also promoted chemokine CXCL1(KC) production in mixed glia. Our data suggest that activation of CD40 mediated signaling may result in increased production of chemokines that may interfere with retroviral replication. Future studies will be directed to specifically delineate CD40 downstream target involved in antiretroviral response in glial cells.