IMMUNOPHENOTYPIC AND ULTRASTRUCTURAL EVIDENCE OF THE LANGERHANS CELL ORIGIN OF THE CANINE CUTANEOUS HISTIOCYTOMA

Canine cutaneous histiocytoma (CCH), a histiocytic benign, dermal, sel f-healing tumor in the young dog, and epidermal Langerhans cells (LC) are thought to be related. In this study, we used immunohistochemical staining and transmission electron microscopy for 5 fresh CCH and 17 f ixed tumors, to examine if, on the basis of their immunophenotype and their ultrastructural morphology, these tumor cells originate as LCs. The immunophenotype of CCH: canine CD11a, 11c, 18, 45, MHC II positive and ACM1, human CD14 negative, was different from canine macrophage i mmunophenotype but very similar to the canine LC phenotype. Furthermor e, we have described ultrastructural markers in CCH cells for the firs t time: these consist of coated vesicles, regularly laminated bodies, pleiomorphic inclusions, paracrystalline structures, and deep invagina tions of the plasma membrane, usually observed in congenital self-heal ing histiocytosis, a human LC tumor, or occasionally observed in human LC. The occurrence of such immunophenotype and ultrastructural marker s confirmed the common lineage of LCs and CCH cells.