Cytolytic activity and associated serine protease expression by skin and afferent lymph CD8+ T cells during orf virus reinfection.

Following orf virus reinfection in sheep, CD8+ T cells were recruited to the lesion site in the skin during the period of viral replication and appeared in increased numbers in afferent lymph draining the infection site. A proportion of the CD8+ T cells were activated, particularly in the skin, as determined by their expression of the cytolytic cell-associated serine protease, BLT-esterase. This was a useful marker for activated cytolytic cells as there was a good correlation between afferent lymph CD8+ T cell-mediated lysis of autologous orf virus-infected skin cells and their expression of BLT-esterase in vitro. The majority of the cells that expressed BLT-esterase in the skin and lymph were CD8+ T cells and cytolysis in vitro was predominately by the MHC class I antigen presentation pathway. The conclusion is that orf virus reinfection is characterized by limited viral replication and stimulation of an activated CTL response in the skin.