Phenotypic characteristics and significance of reticular meshwork surrounding splenic white pulp of mice.

This report describes the phenotypic characteristics of the reticular meshwork (RM) localized between the marginal zone and white pulp of mice. Considered from an anatomical point of view, RM contributes to the migration of lymphocytes into splenic white pulp. We divided the RM into two parts: one surrounding the periarterial lymphoid sheaths (PALS) and the other surrounding the follicles. Throughout both locations of RM, alkaline phosphatase activity was noted on the plasma membrane of the reticular cells and tenascin was expressed on the collagen fibrils in the matrix of the reticular fibers. In contrast, the expression of MAdCAM-1, one of the homing receptors of lymphocytes, was solely confined to the plasma membranes of the fiber-forming reticular cells and processes of the perifollicular RM. In aly mice with defective perifollicular RM and loss of MAdCAM-1 expression, lymphocyte homing to the white pulp was remarkably inhibited, and the compartmentalization of T and B cells did not occur. This fact supports the notion that perifollicular RM plays an essential role in lymphocyte homing and compartmentalization.