Immunohistological investigations in chronic cutaneous leishmaniasis in Saudi Arabia.

The distribution and numbers of IgG-, IgA-, IgM-, and lysozyme-positive cells were investigated by the immunoperoxidase method in paraffin-sections of 13 cases of chronic cutaneous leishmaniasis of low parasite load from Saudi Arabia. The majority of the peroxidase-positive plasma cells contained IgG, whereas the numbers of IgA+ and IgM+ plasma cells were not so numerous. Small groups of squamous epithelial cells showed immunoreactivity for IgG and IgA. Similar positive staining was observed extracellularly in the oedematous upper dermis, in the endothelial cells, and in the perivascular space. The activated macrophages showed strong and diffuse peroxidase staining for lysozyme, whereas epithelioid cells and multinucleated giant cells were negative or had finely granular and considerably weaker staining. It is suggested that humoral immunity also participates in the elimination of the parasites and an immunologically induced necrosis might be responsible for the ulceration of the skin in cutaneous leishmaniasis. It is also assumed that the lysozyme immunoreactivity can be a marker of the activation state of the macrophages.