Dose Ranging Study Comparing the Efficacy, Safety and Pharmacokinetics of Intravenous Infusions of ABT-874 vs Placebo in Subjects With Active Crohn's Disease

Inclusion Criteria: * Diagnosis of Crohn's disease for greater than 4 months confirmed by endoscopy or radiologic evaluation. * CDAI score of \>= 220 and \<= 450 at Week 0. * Males and females \>= 18 years and \< 75 years of age at the Screening visit. * Judged to be in generally good health as determined by the Investigator. Exclusion Criteria: * Current diagnosis of the colitis other than Crohn's disease. * Symptomatic known strictures. * Surgical bowel resections within the past 6 months or is planning any resection at any time point while enrolled in the study. * Ostomy or ileoanal pouch. (Subjects with a previous ileo-rectal anastomosis are not excluded). * Short bowel syndrome as determined by the investigator. * Infection or risk factors for severe infections. * Females who are pregnant or considering becoming pregnant during the study, or breast-feeding.