Immunophenotyping of Nonneoplastic and Neoplastic Histiocytes in Cats and Characterization of a Novel Cell Line Derived From Feline Progressive Histiocytosis.

Histiocytic proliferative diseases are rare in cats, and their pathogenesis is poorly understood. In the present study, 25 cases of histiocytic sarcoma (HS) and 6 of feline progressive histiocytosis (FPH) were examined, and survival times were recorded in 19 cases. The immunophenotypes of tumor cells in these cases as well as of nonneoplastic feline histiocytes were characterized using formalin-fixed, paraffin-embedded tissues. An FPH cell line (AS-FPH01) and xenotransplant mouse model of FPH were also established. The median survival time of HS (150 days) was significantly shorter than that of FPH (470 days). Immunohistochemically, nonneoplastic histiocytes were immunopositive for various combinations of Iba-1, HLA-DR, E-cadherin, CD204, CD163, CD208, and MAC387. By immunohistochemistry, dermal interstitial dendritic cells (iDCs) and macrophages were CD204+/E-cadherin-, while epidermal Langerhans cells (LCs) were CD204-/E-cadherin+. Neoplastic cells of 4 FPH and 18 HS were CD204+/E-cadherin- (iDC/macrophage immunophenotype), while 2 FPH and 2 HS were CD204-/E-cadherin+ (LC immunophenotype), and 5 HS were CD204+/E-cadherin+ (LC-like cell immunophenotype). Furthermore, immunohistochemical and western blot analyses of AS-FPH01 cells derived from E-cadherin-negative FPH revealed that cultured cells were immunopositive for both CD204 and E-cadherin in vitro and in vivo. These results indicate that the neoplastic cells of feline HS and FPH were variably positive for iDC/macrophage and LC markers, and their immunophenotype changed in different microenvironments. The novel cell line established in the present study may serve as an experimental model of FPH that will enable further molecular and therapeutic studies on this disease.