( ( that is ) ( , ( ( ( ( ( factors ( in ( the ( immune system ) ) ) ) , ) ( including antibodies ) ) , ) ( ( ( ( attack cells ) ( in ( ( the ( person 's ) ) ( own body ) ) ) ) ( as ( if ( they ( were ( foreign substances ) ) ) ) ) ) . ) ) ) )
(ROOT (S (ADVP (DT that) (VBZ is)) (, ,) (NP (NP (NNS factors)) (PP (IN in) (NP (DT the) (JJ immune) (NN system))) (, ,) (PP (VBG including) (NP (NNS antibodies))) (, ,)) (VP (VBP attack) (NP (NNS cells)) (PP (IN in) (NP (NP (DT the) (NN person) (POS 's)) (JJ own) (NN body))) (SBAR (RB as) (IN if) (S (NP (PRP they)) (VP (VBD were) (NP (JJ foreign) (NNS substances)))))) (. .)))
that is, factors in the immune system, including antibodies, attack cells in the person's own body as if they were foreign substances.
(ROOT (S (NP (DT The) (JJ immune) (NN system)) (ADVP (RB typically)) (VP (VP (VBZ recognizes)) (, ,) (VP (VBZ attacks)) (, ,) (CC and) (VP (VBZ destroys) (NP (NP (JJ foreign) (NNS cells) (CC or) (NNS substances)) (SBAR (WHNP (WDT that)) (S (VP (MD may) (VP (VB cause) (NP (NN disease))))))))) (. .)))
The immune system typically recognizes, attacks, and destroys foreign cells or substances that may cause disease.