Collagen phagocytosis in multicentric reticulohistiocytosis

A large number of dermal cells engaged in collagen phagocytosis were observed in a case of multicentric reticulohistiocytosis. These cells apparently start to engulf collagen by deep invaginations of the plasma membrane. Fusion of phagosomes containing the engulfed collagen with vesicles probably originating from the Golgi apparatus would give rise to secondary lysosomes. The process of collagen degradation leads to the appearance of fine fibrils and myelin bodies. The presence in the dermis of unusually thick collagen fibers might contribute to this process which appears to occur only under particular physiological and pathological conditions.