CANINE CUTANEOUS HISTIOCYTOMA IS AN EPIDERMOTROPIC LANGERHANS CELL HISTIOCYTOSIS THAT EXPRESSES CD1 AND SPECIFIC BETA(2)-INTEGRIN MOLECULES

Canine cutaneous histiocytoma (CCH) is a common, benign neoplasm of th e clog, Histiocytomas most commonly occur as solitary lesions that und ergo spontaneous regression. The age-specific incidence rate for histi ocytomas drops precipitously after 3 years, although histiocytomas occ ur in dogs of all ages. Langerhans cells (LCs) in humans and dogs expr ess abundant major histocompatibility complex class II molecules and a variety of leukocyte antigens characteristic of dendritic cell differ entiation including CD1a, CD1b, CD1c, and CD11c, The immunophenotype o f CCH resembled that of cutaneous LCs by virtue of the expression of c ol molecules (CD1a, -b, and -c), CD11c, and major histocompatibility c omplex class II. Furthermore, histiocytoma cells had a tropism for epi dermis, which was also consistent with an epidermal LC lineage. The ex pression of adhesion molecules such as CD11b (variable), CD44, CD54 (I CAM-1), and CD49d (VLA-4) ill ccn indicated that the infiltrating cell s had some of the characteristics of activated LCs, as these molecules are not expressed by normal, resting canine epidermal LCs, CCH did no t express Thy-1 or CD4. Thy-1 expression is a characteristic of human and canine dermal dendrocytes, which are perivascular dendritic antige n-presenting cells closely related to epidermal LCs, CD4 expression is prevalent in human LC histiocytosis, and in this respect CCH differed front human LC histiocytosis. Here we demonstrate that CCH is a local ized form of self-limiting LC histiocytosis, which predominately expre sses an epidermal LC phenotype. CCH occurs as solitary or, less common ly, as multiple cutaneous nodules or plaques, which rarely may extend beyond the skin to local lymph nodes. Regression of CCH occurs spontan eously in the vast majority of cases in primary, and secondary sites, and is mediated by CD8(+) alpha beta T cells. The high frequency, of c cn within the general canine population offers the potential that the dog may provide an interesting model system to further the understandi ng of LC proliferative disorders, particularly the self-limiting, cuta neous form of human LC histiocytosis.