The Origin of Melanomacrophages Centers in Salmo Gairdneri Richardson

Abstract

By definition, melanomacrophage centres (MMC) consist of aggregates of macrophage‐like pigmented cells located in the kidney and spleen, and to a lesser extent in the liver. In 30 Salmo gairdneri Richardson trout, MMC have been identified in various organs. In the kidney, liver and spleen, respectively, macrophages (MØ) are aggregated in clusters, which are next to vessels. MMC have been cytoenzymatically identified with periodic acid Schiff (PAS), α‐naphthyl acetate esterase (ANAE), peroxidase (PEROX) reactions. Finally, in order to show pigments in the context of MMC, in particular, we used iron stain to detect iron pigments and Prussian blue reaction to detect melanin and lipofuscin. The presence of iron pigments indicates that MMC function as lymphoreticular centres where fish erythrocytes (FE) are destroyed together with other foreign material. In previous studies, we found that FE are able to bind and engulf Candida albicans (CA) without killing this fungus. FE containing engulfed CA form with MØ functional rosettes and, in reason of that MØ are solicited to phagocytose and kill CA. It is likely that rosettes and/or single FE containing engulfed foreign material migrate to distant organs, such as the kidney, the spleen and the liver. Therefore, the MMC may, in part, derive from these peripheral rosettes and pigments result from FE and foreign material digestion and destruction operated by MØ. Reference Passantino, L., Cianciotta, A., Jirillo, F., Carrassi, M., Jirillo, E. and Passantino, G.F. 2005: Lymphoreticular system in fish: erythrocyte‐mediated immunomodulation of macrophages contributes to the formation of melanomacrophage centers. Immunopharmacol Immunotoxicol. 27, 147–161.