The long‐term evolution of mycobacterial BCG and preformed immune complex BCG/anti‐BCG granulomas in rats

Abstract

In previous studies it was found that infections with BCG or complexed BCG/anti-BCG in rat skin produced granulomas that appeared to resolve at 8 months. In this follow-up study 1 year later, it appeared that while lesions due to performed complexes had resolved, those due to BCG alone had undergone a massive reactivation. Nevertheless despite the loss of CMI the infection was restricted. The bacilli, present in enormously increased numbers, were dead; the host macrophages were large and activated. Epithelioid cells and dendritic cells were common. The granuloma was confluent, with patchy necrosis and inconspicuous polymorph infiltration. Although preformed complexes with viable bacilli formed at equivalence had produced a resolving lesion, the outcome of the natural infection was complicated by an imponderable balance of immunological responses. CMI does not appear to have been a determinant during the crucial phases of the infection.