COMPARATIVE IMMUNOHISTOCHEMICAL STUDY OF STELLATE CELLS IN NORMAL CANINE AND EQUINE ADENOHYPOPHYSES AND IN PITUITARY-TUMORS

The presence and distribution of S100 protein (alpha and beta subunits ), cytokeratin polypeptides, glial fibrillary acidic protein, neurofil aments, vimentin, neuron specific enolase, synaptophysin, HLA class II DR antigen, and pituitary hormones (prolactin, adrenocorticotropic ho rmone and human chorionic gonadotrophin) in stellate cells were studie d immunohistochemically in four normal canine pituitary glands, five c anine pituitary adenomas, two canine pituitary carcinomas and two equi ne pituitary adenomas (with surrounding normal glandular tissue). Stel late cells of the pars distalis and pars intermedia of canine and equi ne adenohypophyses showed a strong reaction with antibodies against S1 00 protein subunits alpha and beta. They also reacted with antibody ag ainst high and low molecular weight cytokeratins, but not with those a gainst other intermediate filament proteins, neuroendocrine markers, t he HLA-class II DR antigen or the pituitary hormones. Other population s of cells expressing both subunits of the S100 protein were polygonal cells of the pars distalis of the adenohypophysis (horse) and margina l epithelial cells of the pars intermedia of the adenohypophysis (dog and horse). Some pituitary tumours had S100-immunoreactive cells with a distribution of alpha and beta subunits that differed between the tw o species. Some canine tumours (one adenoma and one carcinoma) express ed only the alpha subunit, but both of the equine adenomas expressed a lpha and beta protein subunits. Some of the S100-immunoreactive tumour cells reacted with RCK-102 (cytokeratins 5+8) antibody in the dog but not in the horse. The results suggested that canine and equine stella te cells of the adenohypophysis are more closely related to epithelial than to glial cells, as is the case in cattle, sheep and goats but no t human beings or mice. No subpopulation of cells of bone marrow origi n could be identified among canine stellate cells, as they lack MHC cl ass II antigen. The results also suggested that the presence of S100-i mmunoreactive cells is more striking in canine and equine tumours than in human tumours. (C) 1998 W.B. Saunders Company Limited.