Poxvirus-encoded TNF receptor homolog dampens inflammation and protects the host from uncontrolled lung pathology and death during respiratory infection

Ectromelia virus (ECTV) causes mousepox, a surrogate mouse model for smallpox caused by variola virus in humans. Both viruses encode tumor necrosis factor receptor (TNFR) homologs termed cytokine response modifier (Crm) proteins, containing a TNF-binding domain and a chemokine-binding domain termed smallpox virus-encoded chemokine receptor (SECRET) domain. Infection of ECTV-resistant C57BL/6 mice with an ECTV CrmD deletion mutant resulted in uniform mortality due to excessive TNF secretion and dysregulated inflammatory cytokine production but viral load was not affected. CrmD dampened lung pathology, leukocyte recruitment and inflammatory cytokines including TNF, IL-6, IL-10 and IFN-{gamma}. Blockade of IL-6, IL-10R or TNF function with monoclonal antibodies reduced lung pathology and provided 60-100% protection from an otherwise lethal infection. IFN-{gamma} caused lung pathology only when both the TNF-binding and SECRET domains were deleted but it was neither necessary nor sufficient to cause pathology when only the CrmD SECRET domain was expressed by virus.