Local epidermal viral infections: comparative aspects of vaccinia virus, herpes simplex virus and human papillomavirus in man and orf virus in sheep

Anatomically restricted synergistic antiviral activities of innate and adaptive immune cells in the skin

Despite extensive ex vivo investigation, the spatiotemporal organization of immune cells interacting with virus-infected cells in tissues remains uncertain. To address this, we used intravital multiphoton microscopy to visualize immune cell interactions with virus-infected cells following epicutaneous vaccinia virus (VV) infection of mice. VV infects keratinocytes in epidermal foci and numerous migratory dermal inflammatory monocytes that outlie the foci. We observed Ly6G(+) innate immune cells infiltrating and controlling foci, while CD8(+) T cells remained on the periphery killing infected monocytes. Most antigen-specific CD8(+) T cells in the skin did not interact with virus-infected cells. Blocking the generation of reactive nitrogen species relocated CD8(+) T cells into foci, modestly reducing viral titers. Depletion of Ly6G(+) and CD8(+) cells dramatically increased viral titers, consistent with their synergistic but spatially segregated viral clearance activities. These findings highlight previously unappreciated differences in the anatomic specialization of antiviral immune cell subsets.

Ehrlichia (Cytoecetes) phagocytophila predisposes to severe contagious ecthyma (Orf ) in lambs

Eight lambs experimentally infected with Ehrlichia (Cytoecetes) phagocytophila 7 days before exposure to orf virus were compared with control lambs infected with orf virus alone. The dually infected animals differed from the controls in showing skin lesions of greater severity, prolonged viral shedding, and lower antibody titres. Infection with E. phagocytophila had no significant effect on virus-specific lymphocyte proliferation. Such proliferation was detected in the peripheral blood of all lambs as early as 7 days after exposure to orf virus.