Anatomical pathways from the white to the red pulp in the human spleen.

In the human spleen we failed to find marginal zone bridging channels which in rats and mice are said to serve as return routes for lymphocytes from the white into the red pulp. In human spleens, using anticartilaginous antisera which distinctly visualized extracellular structures, in some parts we found the periarterial lymphocyte sheath to be closely attached to the red pulp, so that lymphocytes and other material could pass from the white pulp directly into the red pulp and vice versa. The strips of reticular fibres that seemed to bridge the marginal zone between the follicles and the red pulp proved to be components of reticular structures around the arteries, passing from the periarterial lymphocyte sheath into the follicles or from the follicles through the marginal zone into the red pulp.