Detection of cellular cytokine mRNA expression during orf virus infection in sheep: differential interferon-gamma mRNA expression by cells in primaryversus reinfection skin lesions

In sheep infected with the parapoxvirus orf virus, primary infection orf sk in lesions developed and resolved within 8 weeks. Reinfection lesions were smaller and resolved within 3 weeks. The host response in the skin was char acterized by an accumulation of neutrophils, dendritic cells, CD4(+) T cell s, CD8(+) T cells, B cells and T19(+) gamma delta T cells. The magnitude of this accumulation paralleled orf virus replication in the skin. In situ hy bridization was used to detect cells expressing interferon-gamma (IFN-gamma ), tumor necrosis factor-alpha (TNF-alpha) and interleukin-4 (IL-4) mRNAs i n orf skin. Cells expressing IL-4 mRNA were not detected at any time after infection. Cells expressing IFN-gamma mRNA were detected after reinfection but not after primary infection. Cells expressing TNF-alpha mRNA included e pidermal cells, vascular endothelium and uncharacterized cells that increas ed more rapidly in the skin after reinfection compared to primary infection . The results are consistent with a prominent role for IFN-gamma in the hos t immune response controlling the severity of the disease. (C) 2001 Elsevie r Science B.V. All rights reserved.