Phenotypic characterisation of the dendritic cells accumulating in ovine dermis following primary and secondary orf virus infections

Orf virus, a member of the parapoxvirus genus, causes a localised epidermal infection in sheep, and can be transmitted to man. The most striking local response to infection in sheep is the accumulation of a network of MHC class II+ denadritic cells (DCs) in the dermis below the lesion. In the present study these DCs were further characterised following experimental infection of sheep. Four subpopulations of MHC class II+ DCs were distinguished within normal ovine skin. The network observed in response to primary and secondary orf virus infections compnsed two of the resident types. The accumulating DCs lacked the CD1 antigen found on 45% of the resident dermal dendritic cells and a proportion expressed factor XIIIa. The highest number of factor XIIIa(+) DCs accumulated in a primary infection, with small numbers appearing only transiently in a secondary infection. The majority of DCs in the primary lesions and all those in the secondary orf lesions did not appear to be proliferating and their lack of expression of CD11b or CD11c antigens indicated that they were not macrophages.