Unusual structure of human splenic sinusoids revealed by monoclonal antibodies.

The sinusoid of the human spleen is an unusual vascular structure which is involved in the removal of damaged or aged erythrocytes. The sinusoid also permits the migration of leukocytes from the cords of Billroth into the circulation. The sinusoids were studied with a variety of monoclonal antibodies in an effort to further delineate their structure. Immunohistochemical studies of sinusoids with antibodies to the intermediate filament protein vimentin and the T cell antigen Leu 2 revealed unusual rod-shaped and banded structures. These structures are distinct from the annular fibers detected by histochemical methods. They are not detected in other types of endothelium. The sinusoids are also distinct in that they fail to react with antibody Leu M3 which stains other types of endothelium. The sinusoids are similar to other types of endothelium in their immunoreactivity with antibodies to Factor VIII and HLA-DR antigens.