Spontaneous lesions detected in the common cotton-eared marmosets (Callithrix jacchus).

Spontaneous lesions in the common cotton-eared marmosets (Callithrix jacchus), which were maintained in our laboratory or were purchased from a commercial breeder, were examined histopathologically. There were 39 males and 22 females, between the ages of 7 and 100 months. The most interesting finding noted was extramedullary hematopoiesis, which was observed in the mesenteric lymph nodes, spleen, liver, kidney, adrenal gland, and cerebral choroid plexus. Megakaryocytes were frequently observed in the blood vessels of the alveolar wall of the lung. It is important to distinguish extramedullary hematopoiesis which occurs accidentally from that induced by repeated blood sampling or that resulting from administration of chemicals. Extramedullary hematopoiesis was easily distinguishable from inflammation or hematopoietic neoplasms, because of the various cellular elements present, including megakaryocytes. In the weak and dead animals, enterocolitis was found at a high frequency. Other common findings included thymic involution, prominent vacuolation of liver sinusoidal cells, which were probably Ito-cells, and basophilic changes in the renal tubular epithelium. The liver and the kidney are frequently affected by toxic effects of chemicals. Therefore, it is important to distinguish the toxic changes from the spontaneous ones. Proliferation of apocrine glands in the cervical skin was an interesting finding; however, neither inflammatory change nor cellular atypia was noted in this structure. Although its function is unclear, this structure may be a marmoset-specific tissue.