Splenic marginal zone lymphocytes and related cells in the lymph node: a morphologic and immunohistochemical study.

The marginal zone of the spleen contains a well-defined population of lymphocytes with an unknown function. The question is whether this cell population is unique to the spleen or is it also present in the lymph node. These cells have medium-sized nuclei and a moderate amount of cytoplasm. Immunohistochemistry and enzyme histochemistry revealed a marker pattern by which these cells could be distinguished from the lymphocytes of the mantle zone of the spleen: IgD-, CD23-, KiB3-, and alkaline phosphatase+. In the lymph node, the outer side of the follicular mantle contains a subpopulation of B lymphocytes with a similar morphology and the same marker pattern. This subpopulation differs from the marginal zone cells in the spleen in that it does not form a distinct zone. These cells are especially prominent in lymph nodes with fatty atrophy. Their relationship to other subpopulations of B lymphocytes and to malignant lymphomas is evaluated but remains questionable.