Observations on the onset of delayed type hypersensitivity reactions to Dermatophilus congolensis in rats and guinea-pigs

Abstract

Dermatophilus congolensis infections applied to areas of skin which are already showing a cell mediated response to l-chloro-2, 4—dinitrobenzene (D.N.C.B.) give rise to lesions in laboratory animals, from which zoospores may be recovered over significantly longer periods and in larger numbers than in control animals. Such an increased chronicity had been suggested as an important step in the search for a laboratory model of the economically and clinically significant chronic field condition. This project investigated the / hypothesis that a delay in the onset of cell mediated responses to D. congolensis infections is caused by the preexisting hypersensitive reaction to D.N.C.B. at the site of infection. Any such delay could support this explanation for the increased recovery period of D. congolensis zoospores.

Experiments were carried out on groups of both rats and guinea- pigs, both D.N.C.B. sensitised and control animals. In guinea-pigs skin tests were used to monitor the cell mediated response to D. congolensis antigen. Skin tests proved unsatisfactory in rats and a direct Macrophage Migrations Inhibition test was developed and used in their place.

In neither species did the D.N.C.B. sensitisation have a significant effect on the course of the onset of cell mediated responses to D. congolensis antigens. It was however recorded that the lesions induced by scarification of the skin sites showing an hyperimmune response to D.N.C.B. were grossly more severe than those in control animals.

Delay in cell mediated responses to D. congolensis does not appear to be a factor in the increased "chronicity" of zoospore recovery from infection sites showing a hyperimmune response to D.N.C.B..