The immunopathology of actinomycetoma lesions caused by Streptomyces somaliensis

The immune responses in actinomycetoma lesions caused by Streptomyces somaliensis in Sudan were characterized by immunohistochemistry during 1997-1998. In sections stained with haematoxylin and eosin, the inflammatory reaction around the grain was of 2 types. In type I there were 3 zones: a neutrophil zone immediately around the grain, an intermediate zone containing mainly macrophages, and a peripheral zone consisting of lymphocytes and plasma cells. Zone 1 stained positively for CD15 (neutrophils), zone 2 for CD68 (macrophages) and CD3 (T lymphocytes), and zone 3 for CD20 (B lymphocytes). In the type II reaction, there was no neutrophil zone, the grains being surrounded only by macrophages and giant cells. This was confirmed by immunohistochemistry, which demonstrated the presence of CD3 positive cells. Immunoglobulins G and M and complement were demonstrated on the surface of the grain and on filaments inside the grain. Neutrophils and macrophages were recruited into the lesion by complement and were involved in the fragmentation of the grain. The cytokine profile in the lesion and regional lymph nodes was of a dominant Th2 pattern (interleukins-10 and 4).