LEUKOCYTE DIFFERENTIATION ANTIGENS IN CANINE CUTANEOUS AND ORAL PLASMACYTOMAS

Seventeen cutaneous and oral tumours with light microscopic features o f plasmacytomas from 16 dogs were studied. Clinically, most neoplasms were benign: although three recurred after excision and three were loc ally invasive. Tumours most often arose on the pinnae, digits, gingiva , and inguinal regions near areas of chronic inflammation and exhibite d variable degrees of plasmacytic differentiation microscopically. Dia gnosis of plasmacytoma was confirmed in paraffin-embedded tissues with a panel of leukocyte differentiation antigen markers that included cr oss-reactive antibodies for Mb-1 (CD79a), CD3, and vimentin and canine -specific antibodies for CD45RA and CD18. Immunoreactivity for Mb-1 an d CD45RA, including staining of multinucleate cells and cells with kar yomegaly, confirmed a B-cell origin of neoplasms, while staining for C D3 and CD18 revealed an extensive network of infiltrative T-cells and dendritic cells in tumours suggestive of a directed immune response. T hese findings (i) demonstrate the value of using a panel of antibodies for leukocyte antigens to differentiate plasmacytomas from other cuta neous and oral round cell tumours, and (ii) suggest that immune recogn ition and responsiveness within tumours may play a role in the behavio ur of plasmacytomas in dogs by affecting tumour cell growth and differ entiation.