( That ( ( ( triggers ( ( ( the ( complement cascade ) ) , ) ( ( a series ) ( of ( ( 20 proteins ) ( in ( the ( blood serum ) ) ) ) ) ) ) ) ( that ( ( ( clog arteries ) and ) ( ( kill ( any ( graft cells ) ) ) ( ( the blood ) ( can reach ) ) ) ) ) ) . ) )
(ROOT (S (NP (DT That)) (VP (VBZ triggers) (NP (NP (DT the) (JJ complement) (NN cascade)) (, ,) (NP (NP (DT a) (NN series)) (PP (IN of) (NP (NP (CD 20) (NNS proteins)) (PP (IN in) (NP (DT the) (NN blood) (NN serum))))))) (SBAR (IN that) (S (S (VP (VBG clog) (NP (NNS arteries)))) (CC and) (S (VP (VB kill) (NP (DT any) (NN graft) (NNS cells)) (SBAR (S (NP (DT the) (NN blood)) (VP (MD can) (VP (VB reach)))))))))) (. .)))
That triggers the complement cascade, a series of 20 proteins in the blood serum that clog arteries and kill any graft cells the blood can reach.
(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)))))))) (. .)))