Delayed type hypersensitivity (DTH): quantitative studies of mycobacteria-induced destructive and non-destructive DTH-reactions in the skin of guinea pigs.

Research on delayed type hypersensitivity (DTH) to facultative intracellular bacteria in guinea pigs focused especially on intracutaneous DTH reactions. However, phenomena of erythematous and necrotic skin reactions were only evaluated qualitatively, dose-response relationships not investigated, differences between early and late reactions overlooked and the development of unspecific skin necrosis ignored. In this work, these aspects were investigated by characterisation of DTH-mediated reactions against mycobacterial antigens in the skin of guinea pigs. Intracutaneous injection of mycobacterial antigen into the skin of immunised and non-immunised guinea pigs induced an erythematous reaction which reached its peak after 24 h. On days two and three after challenge, the centre of the erythema blanched and necrotised. During the next days, skin necrosis increased and reached a peak on days six and seven. In immunised guinea pigs, DTH led to a specific enhancement of erythematous and necrotising skin reactions which also appeared in non-immunised guinea pigs. Thus, an early erythematous and a late necrotising DTH-reaction were identified by their morphology and time course. Both types of DTH-mediated allergy revealed dose-dependency from the intracutaneously injected antigen doses. Erythematous and necrotising DTH reactions against viable and killed mycobacteria showed a similar time course and morphology. DTH reactivity which was induced by immunisation with Mycobacterium tuberculosis showed cross-reactivity with antigens of Mycobacterium bovis.