AN SEM STUDY OF LYMPHOCYTE EXTRAVASATION IN THE MOUSE SPLEEN

Although it is well established that mammalian lymphocytes leave the circulatory system and enter the white pulp of the spleen, little is known about the mechanism of their movement. This study attempts to shed some light on the mechanism of lymphocyte movement into the spleen. Graft-versus-host reactions were induced in mice by injecting parental lymphocytes into F₁ hybrids. Experimental and control spleens were fixed, dehydrated, embedded in paraffin, fractured, and studied using the scanning electron microscope. The marginal sinus wall was examined for lymphocyte migration between the cells of the endothelium. Experimental mice showed many lymphocytes in the marginal sinus migrating into and/or out of the white pulp through fenestrations between cells. Control mice showed little or no sign of lymphocyte migration. We suggest that the lymphocytes move out of the arteriole into the white pulp through the endothelium of the marginal sinus.