Spleen is one of the two major secondary lymphatic organs which filters any worn-out old red blood cells from the blood and fights infections with lymphocytes and monocytes (cells that engulf and devour antigens). It is also the largest lymphatic organ in the body. In addition, the spleen acts as a reservoir for blood and any rupture to the spleen can cause dangerous internal bleeding. The spleen is also a site for immune function, since it contains lymphatic tissue and produces lymphocytes. However, the human body has the capability of functioning without the spleen if it becomes injured or diseased.

Peyer's patches is the other major secondary lymphatic organs which removes intestinal antigens (foreign or harmful substances in the body)