Phenotypic characterization of histiocytes infiltrating a leiomyofibrosarcoma

We described previously a unique cutaneous tumour in a young pig, which was characterized by several criteria as a histiocytic leiomyofibrosarcoma. The lipid-laden macrophages (histiocytes) which permeated the tumour were CD2+/CD18+/CD49d+ but MAC387 (L1 antigen) and CD15 negative. The present study compared the phenotypes of histiocytes in tumour metastases in the liver with resident liver macrophages, revealing differential expression of certain macrophage activation markers. After repeated subcutaneous passage of the tumour in athymic (nu/nu) mice, flow cytometry demonstrated a rapid loss of porcine MHC Class II, but a more prolonged expression of porcine MHC Class I, consistent with our immunohistological observations. Mouse macrophages (CD2+/F4.80+) infiltrated the later-passage tumours, suggesting that the histiocytes were not of neoplastic origin.