( ( ( ( ( ( Studying genes ) ( for complement ) ) , ) ( ( a series ) ( of ( proteins ( in ( ( the blood ) ( that ( play ( ( an ( important part ) ) ( in ( the ( immune system ) ) ) ) ) ) ) ) ) ) ) ) , ) ( ( is ( ( another ( active area ) ) ( of ( lupus research ) ) ) ) . ) )
(ROOT (S (NP (NP (NP (VBG Studying) (NNS genes)) (PP (IN for) (NP (NNP complement)))) (, ,) (NP (NP (DT a) (NN series)) (PP (IN of) (NP (NP (NNS proteins)) (PP (IN in) (NP (NP (DT the) (NN blood)) (SBAR (WHNP (WDT that)) (S (VP (VBP play) (NP (NP (DT an) (JJ important) (NN part)) (PP (IN in) (NP (DT the) (JJ immune) (NN system)))))))))))) (, ,)) (VP (VBZ is) (NP (NP (DT another) (JJ active) (NN area)) (PP (IN of) (NP (JJ lupus) (NN research))))) (. .)))
Studying genes for complement, a series of proteins in the blood that play an important part in the immune system, is  another active area of lupus research.
(ROOT (S (NP (DT The) (JJ complement) (NN system)) (VP (VBZ is) (NP (NP (DT a) (NN series)) (PP (IN of) (NP (NP (NNS proteins)) (VP (ADVP (RB constitutively)) (VBN found) (PP (IN in) (NP (DT the) (NN blood) (NN plasma)))))))) (. .)))