A multicenter (more than one medical research center involved in study), randomized (study drug assigned by chance), double-blind (neither the Investigator nor the participant know about the study drug), placebo-controlled, proof-of-concept study of ustekinumab in participants with active systemic lupus erythematosus. Participants will be screened to achieve all inclusion criteria and none exclusion criteria and will then receive either ustekinumab or placebo along with concomitant background medicine. Participants will be primarily assessed for response using the Systemic Lupus Erythematosus Response Index 2000 (SRI-4). Participants' safety will be assessed throughout the study.