Maturation and function of human dendritic cells are inhibited by orf virus-encoded interleukin-10

Orf virus (ORFV) is a parapoxvirus that infects sheep, goats and man. In humans, the virus induces acute, pustular skin lesions that can develop into a progressive disease. Humans are susceptible to reinfection with ORFV and rare cases of persistent infection have been reported. ORFV encodes several immunomodulators, including a homologue of interleukin-10 (ORFV IL-10), that may explain these phenomena. The immunosuppressive effects of ORFV IL-10 on immature human dendritic cells (DCs) cultured from blood-derived monocytes (MoDCs) were investigated. MoDCs exposed simultaneously to lipopolysaccharide and ORFV IL-10 showed enhanced ovalbumin-FITC uptake and reduced IL-12 expression, indicating inhibition of maturation. Moreover, ORFV IL-10 inhibited the upregulation of DC cell-surface activation and maturation markers MHC II, CD80, CD83 and CD86 and inhibited the capacity of MoDCs to activate CD4(+) T cells in an oxidative mitogenesis assay. These findings suggest that ORFV IL-10 may influence the development of acquired immunity in humans by impairing DC function.