The spleen participates in immune and hematologic (blood filtration) functions.

• It clears microorganisms from the blood stream.
• It clears particulate antigens from the blood stream.
• The spleen is specialized to fight bloodborne pathogens. The spleen has areas for making antibodies (follicles) and amplifying antigen-specific T cells (periarteriolar lymphatic sheath, or PALS).
• Synthesis of immunoglobulin G (IgG), properdin (an essential component of the alternate pathway of complement activation), and tuftsin (an immunostimulatory tetrapeptide)
• Extramedullary hematopoiesis in certain diseases