IMMUNOHISTOCHEMISTRY OF THE PROGRESSIVE AND REGRESSIVE STAGES OF BOVINE PAPILLOMATOSIS

The progressive and regressive stages of fibropapilloma in their unusu al papillomatous formation in calves are described. Papillated hyperpl asia of the epidermis and high mitotic activity in stratum basale char acterized the progressive stage. The regressive stage (120 days later) showed infiltration of dermal papillary layer by mononuclear cells (C D3+ cells and macrophages),a thin stratum spinosum without long rete r idges, and massive hyalinization of collagen in the dermis. Several ba sal cells in the mitotic cycle were immunohistochemically positive for papillomavirus. Immunohistochemically, papillomavirus was demonstrate d in these lesions with the higher numbers of virus positive cells in the progressive stage. Some cells in the stratum spinosum showed both cytoplasmic-and nuclear staining for the virus, which implies the budd ing of the virion into the cytoplasm in these layers.