Differential expression of heparan sulfate domains in rat spleen.

The microarchitecture of the spleen is composed of a meshwork of reticulum cells and their matrix. Heparan sulfates (HS) are important components of this meshwork and are involved in processes such as cell adhesion, cell migration, and cytokine/growth factor binding. The expression of HS epitopes was analyzed using anti-HS antibodies. Four different staining patterns were observed, as exemplified by antibodies RB4EA12, HS4E4, AO4B08, and HS4C3. These antibodies recognize different chemical modifications in HS. In adult spleen, RB4EA12 stained only the reticular meshwork and blood vessels in the red pulp and marginal zone. HS4E4 stained blood vessel-associated basal lamina. AO4B08 and HS4C3 stained the reticular meshwork and blood vessels throughout the spleen, but only AO4B08 strongly stained smooth muscle cells and ring fibers. Interleukin-2 localized in the red pulp and marginal zone and was bound to HS. AO4B08, HS4C3, and RB4EA12 but not HS4E4 co-localized with interleukin-2. In 10-day-old spleen, HS4E4 recognized reticular fibers, which were not stained in the adult stage. Immunoelectron microscopy revealed that HS was restricted to basal laminae and reticular fibers. Taken together, data show that HS epitopes are differentially expressed in the spleen and that this may create specific extracellular environments for immunological processes.