Which of the following statements regarding splenic function in humans are true?

a. The specific immune function of the spleen is principally related to its antigen processing role

d. The spleen serves as a principal source of nonspecific opsonins

Immune function of the spleen includes both nonspecific and specific immune responses. Nonspecific immune function is largely characterized by removal of particulate matter by the macrophages. The spleen contains 25% of the fixed tissue macrophage population in the body. The spleen is more efficient than the liver at removal of incompletely opsonized bacteria. The liver is most effective at removing bacteria with a high density of surface opsonins. The spleen also serves as a principal source of nonspecific opsonins. These include tuftsin, properidin, and fibronectin. Tuftsin stimulates granulocyte and macrophage motility and phagocytosis. Properdin activates the alternative pathway of the complement system, leading to complement fixation. Both the activated complement complexes and the complement products facilitate the destruction of the target organism. Fibronectin is a macromolecule that appears to have nonspecific stimulatory activity on the processes of fibrosis and wound healing.

The specific immune functions of the spleen are principally related to its antigen-processing role, and this is in turn dependent on its unique anatomy and the circulation of lymphocytes into the spleen. The liver, not the spleen, is the major site of synthesis of complement pathway proteins.