AN ORIGINAL PERIFOLLICULAR ZONE CELL IN THE CANINE REACTIVE LYMPH-NODE - A MORPHOLOGICAL, PHENOTYPICAL AND ETIOLOGIC STUDY

In this study of 109 canine reactive lymph nodes, the perifollicular z one (PZ) cell was characterized by cytological, histological, immunocy tochemical and electron microscopical techniques. The PZ cell was alwa ys found in association with plasma cell hyperplasia. Its main cytolog ical characteristics were medium size, fine chromatin and a large cent ral prominent nucleolus with a small amount of pale cytoplasm. It was located in a clearly recognizable PZ surrounding the follicles; this z one was particularly well developed at the capsular pole of the lymph node. Electron microscopical findings indicated a poorly differentiate d cell. Immunolabelling indicated a CD3(-), cIg(-), Ki-67(-) immunophe notype, suggesting a resting B cell. These results suggest that the PZ cell belongs either to a post-follicular stage between large immunobl asts and plasma cells or, as is more likely, to a pre-follicular lymph oid subpopulation occurring early in the B-cell differentiation scheme , as with most human marginal zone (MZ) cells. Its high frequency of o ccurrence in reactive lymph nodes in mammary tumour lymphadenopathies, systemic lupus erythematosus and leishmaniasis, suggests that the PZ cell has a special role in the canine immune response, or perhaps in t he arrested maturation of the normal developmental process. (C) 1995 A cademic Press Limited