Functions of the spleen in host defense against infection.

In humans the spleen functions in host defense as a filter and site for phagocytic clearance of the bloodstream. The spleen serves an essential role in this phagocytic clearance if the host has deficient concentrations of opsonizing antibodies. The spleen also produces antibody, and splenic function is required for the host to mount an early IgM response. There is evidence from experiments using animals that the spleen is important in regulating secondary antibody response and in certain aspects of cell-mediated immunity. However, the role of the spleen in these events in the human remains to be defined.