Temporal changes in the granulocytic responses to experimental infection of the skin of mice and sheep with Dermatophilus congolensis.

The patterns of dermal inflammatory cell response to infection with Dermatophilosis congolensis were determined in mice and sheep from histological samples taken before and at intervals after topical application of infective zoospores to ether-swabbed skin. Neutrophils, eosinophils, basophils and mast cells were identified by histochemical staining. Temporal changes in the B cell, T cell, and MHC Class II+ dendritic cell populations form part of a separate report. The filamentous stages of the bacterium were observed in the stratum corneum of both species; in the sheep they were also found in the outer layers of the living epidermis. In both species, large numbers of neutrophils and some lymphocytes penetrated the epidermis and entered the infected surface region. Within the underlying dermis there was an accumulation of dendritic cells immediately below the infected epidermis and evidence of mast cell degranulation; the basophils and eosinophils did not appear to be actively involved. The striking difference between the two species was the duration of the infection and the associated response which, in the mouse, lasted about five days in comparison with over 21 days in the sheep. Neutrophil numbers in the mouse for example were elevated by 12 h and had peaked at 60 h after infection, while in the sheep they did not peak until about 120 h.