Canine cutaneous protothecosis: an immunohistochemical analysis of the inflammatory cellular infiltrate.

In this immunohistochemical study, the distribution of the cellular inflammatory infiltrate associated with cutaneous canine protothecosis (Prototheca wickerhamii) was evaluated by consecutive biopsies taken before, during and after treatment. Antibodies specific to canine immunoglobulins (IgG, IgM, IgA), human CD3 antigen (pan T-lymphocyte marker) and human myeloid/ histiocyte antigen (macrophage/neutrophil marker) were used. Before treatment, cellular infiltrate was very scanty in the inflamed areas, but it increased during the treatment, whereas the number of protothecal organisms decreased. Statistical analysis revealed an inverse relation between the number of protothecal organisms and the number of infiltrating macrophage/neutrophils (P < 0.004), T lymphocytes (P < 0.001), and cells containing immunoglobulin G (P < 0.001), M (P < 0.001) and A (P < 0.001) at different stages of the disease. These findings suggest either that protothecal organisms inhibit the migration or proliferation of cellular inflammatory infiltrate or that only dead protothecal organisms induce an effective local immune response.