CD47 expression attenuates Ebola virus-induced immunopathology in mice.

It has been shown that a very early cell-intrinsic response to infection is the upregulation of CD47 cell surface expression, a molecule known for delivering a "don't eat me signal" that inhibits macrophage-mediated phagocytosis and antigen presentation. Thus, blockade of CD47 signaling during lymphocytic choriomenigitis virus infections of mice has been shown to enhance the kinetics and potency of immune responses, thereby producing faster recovery. It seems counterintuitive that one of the earliest responses to infection would be immunoinhibitory, but it has been hypothesized that CD47 induction acts as an innate immune system checkpoint to prevent immune overactivation and immunopathogenic responses during certain infections. In the current study we examined the effect of CD47 blockade on lethal Ebola virus infection of mice. At 6 days post-infection, CD47 blockade was associated with significantly increased activation of B cells along with increases in recently cytolytic CD8 T cells. However, the anti-CD47-treated mice exhibited increased weight loss, higher virus titers, and succumbed more rapidly. The anti-CD47-treated mice also had increased inflammatory cytokines in the plasma indicative of a "cytokine storm". Thus, in the context of this rapid hemorrhagic disease, CD47 blockade indeed exacerbated immunopathology and disease severity.