In contrast to lymph node GCs where antigen is delivered through the lymphatic system, antigen enters GCs of the spleen through the blood stream. B lymphocytes are concentrated within GCs and surrounding mantle and marginal zones in the splenic white pulp. T lymphocytes are concentrated in the periarteriolar lymphoid sheaths (PALS). The spleen also contains a red pulp comprised of cords and sinuses lined by specialized cells of the mononuclear phagocyte system. These macrophages clear micro-organisms coated with antibody and complement from the bloodstream. The spleen is required for early adaptive response to circulating pathogens, such as occurs in bacterial sepsis.
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