(S (S (BASENP (DT The) (NNS mice)) (VP (VBD had) (NP (BASENP (DT a) (JJ dramatic) (NN reduction)) (PP (IN in) (NP (BASENP (DT the) (NN number) (CC and) (NN activity)) (PP (IN of) (BASENP (NN natural) (NN killer) (NNS cells)))))))) (PERIOD .))