Author's School

Graduate School of Arts & Sciences

Author's Department/Program

Biology and Biomedical Sciences: Molecular Microbiology and Microbial Pathogenesis


English (en)

Date of Award

January 2011

Degree Type


Degree Name

Doctor of Philosophy (PhD)

Chair and Committee

John Atkinson


Poxviruses subvert the host immune response by producing immunomodulatory virulence factors, including a complement regulatory protein. Ectromelia virus provides a mouse model for human smallpox infection where the virus and the host's immune response have also co-evolved. Using this model, we investigated the role of the complement system in a poxvirus infection. Ectromelia virus inoculated via multiple routes caused increased mortality by 7 to 10 days post-infection in C57BL/6 mice that lack C3, the central component of the complement cascade. In C3-/- mice, ectromelia virus disseminated earlier to target organs and generated higher peak titers compared to the congenic controls. Specifically, increased hepatic inflammation and necrosis correlated with these higher tissue titers and likely contributed to the morbidity in the C3-/- mice. In vitro, the complement system in na├»ve C57BL/6 mouse sera neutralized ectromelia virus, primarily through the recognition of the virion by natural antibody and activation of the classical and alternative pathways. Sera deficient in classical or alternative pathway components or antibody had reduced ability to neutralize viral particles, which likely contributed to increased viral dissemination and disease severity in vivo. The increased mortality of C4-/- or Factor B-/- mice also indicates that these two pathways of complement activation are required for survival. The importance of complement in the immune response to poxviruses accounts for why the virus encodes a potent complement regulatory protein, EctroMelia Inhibitor of Complement Enzymes: EMICE). Infected cells produce EMICE within 6–8 hours of infection. Recombinant EMICE produced in E. coli has cofactor activity against C3 and C4, regulates mouse complement, and protects ectromelia virus in vitro. In summary, the complement system acts in the first few minutes, hours, and days to control this poxviral infection, and the virus counters this activity though production of its regulatory protein EMICE.



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