Skin inflammation in RelB^-/- mice leads to defective immunity and impaired clearance of vaccinia virus

Background: Atopic dermatitis (AD) is an inflammatory skin disorder occurring in genetically predisposed individuals with a systemic T_H2 bias. Atopic dermatitis patients exposed to the smallpox vaccine, vaccinia virus (VV), occasionally develop eczema vaccinatum (EV), an overwhelming and potentially lethal systemic infection with VV. Objective: To establish a murine model of EV and examine the effects of skin inflammation on VV immunity. Methods: The skin of RelB^-/- mice, like that of chronic AD lesions in humans, exhibits thickening, eosinophilic infiltration, hyperkeratosis, and acanthosis. RelB^-/- and wild-type (WT) control mice were infected with VV via skin scarification. Viral spread, cytokine levels, IgG2a responses and VV-specific T cells were measured. Results: Cutaneously VV-infected RelB^-/-, but not WT mice, exhibited weight loss, markedly impaired systemic clearance of the virus and increased contiguous propagation from the inoculation site. This was associated with a dramatically impaired generation of IFN-γ-producing CD8⁺ vaccinia-specific T cells along with decreased secretion of IFN-γ by VV-stimulated splenocytes. The T_H2 cytokines-IL-4, IL-5, IL-13, and IL-10-on the other hand, were overproduced. When infected intraperitoneally, RelB^-/- mice generated robust T cell responses with good IFN-γ production. Conclusion: Allergic inflammation in RelB^-/- mice is associated with dysregulated immunity to VV encountered via the skin. We speculate that susceptibility of AD patients to overwhelming vaccinia virus infection is similarly related to ineffective T cell responses. Clinical implications: The susceptibility of patients with AD to EV following cutaneous contact with VV is related to ineffective antiviral immune responses.