( ( ( ( the spleen ) , ) ( which ( is ( ( a gland ) ( that ( ( filters ( ( bacteria and ) ( old ( red ( blood cells ) ) ) ) ) ( from ( the body ) ) ) ) ) ) ) ) ; )
(ROOT (NP (NP (NP (DT the) (NN spleen)) (, ,) (SBAR (WHNP (WDT which)) (S (VP (VBZ is) (NP (NP (DT a) (NN gland)) (SBAR (WHNP (WDT that)) (S (VP (VBZ filters) (NP (NP (NNS bacteria)) (CC and) (NP (JJ old) (JJ red) (NN blood) (NNS cells))) (PP (IN from) (NP (DT the) (NN body))))))))))) (: ;)))
the spleen, which is a gland that filters bacteria and old red blood cells from the body;
(ROOT (S (NP (NP (DT The) (JJ main) (NN function)) (PP (IN of) (NP (DT the) (NN spleen)))) (VP (VBZ is) (S (VP (TO to) (VP (VP (VB filter) (NP (DT the) (NN blood))) (CC and) (VP (VB remove) (NP (JJ unwanted) (JJ red) (NN blood) (NNS cells))))))) (. .)))
The main function of the spleen is to filter the blood and remove unwanted red blood cells.