The homing of lymphocytes into various peripheral lymphoid organs involves a complex set of interactions between the circulating lymphoid cells and the local endothelium. While the initial binding and the adhesion processes of lymphocytes leading to their homing to the lymph nodes have thoroughly been studied, relatively little is known about the lymphoid- endothelial interactions taking place in the spleen. Our aim was to isolate rat monoclonal antibodies (MAbs) against the endothelial cells of the mouse spleen. Using splenic stroma derived from irradiated mice as antigen, two new rat MAbs were isolated. The MAb designated as IBL-7/1 bound to the sinus- lining (littoral) cells in the red pulp, marginal zone, and to the T- and B- cell compartments of the white pulp, respectively. However, it did not react with the central arteriole in the periarteriolar lymphoid sheath (PALS). In contrast to this pattern, the IBL-7/22 MAb recognized a shared antigen expressed by the sinusoidal and arterial endothelium. In addition to the endothelial reactivity, the IBL-7/22 MAb also stained the reticular components of the PALS and red pulp, but not that of the follicles. In vivo labelling with fluorescein (FITC)-conjugated IBL-7/1 MAb followed by confocal microscopic analysis revealed that the antigen recognized was expressed on the luminal surface of the sinusoids. The treatment of mice with IBL-7/1 MAb did not result in the altered distribution of T and B cells. These two new MAbs may be valuable tools for the phenotypic analysis of splenic endothelium, and can be used for the identification of various endothelial cell subpopulations of the mouse spleen.
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