Marginal zones: the major B cell compartment of rat spleens.

The marginal zones of rat and human spleens are a broad band of cells, which surround the small lymphocyte area of the white pulp. Staining for acid phosphatase and alpha-naphthyl acetate esterase activity indicates that the majority of cells in this compartment are intermediate-sized lymphocytes. Macrophages only form a minor component. Using quantitative histology, it is shown that the marginal zones are the largest white pulp compartment in terms of volume. They contain approximately as many lymphocytes as the small lymphocyte zones. The cells of the marginal zone are strongly C3- and Fc receptor-positive. While the cells of this zone have demonstratable surface membrane Ig, it is difficult to exclude that this is not passively absorbed. Other means were therefore sought to determine the lineage of lymphocytes in this area. First, the cells in this zone do not bear appreciable quantities of the rat T cell selective antigen detected by the monoclonal antibody W313. Second, marginal zone cells are present in normal numbers in congenitally athymic "nude" rats. Finally, marginal zones do not become populated with lymphocytes in rats treated from birth with anti-mu antibody. Further experiments showed that marginal zone lymphocytes do not recirculate.