Cohort 1 will consist of 12 subjects (6 AMG 557: 6 placebo) randomized to receive AMG 557 210 mg or matching placebo. Cohort 2 will consist of 12 subjects (6 AMG 557: 6 placebo) randomized to receive AMG 557 140 mg or matching placebo. Enrollment of Cohort 2 (140 mg) will be initiated after enrollment of Cohort 1 (210 mg) is completed. After Cohort 1 and 2 enrollment has been completed, the emerging PK and PD data will be reviewed to determine if an additional 4-8 subjects with SCLE will be enrolled into the study to address equivocal results from the study. These 4-8 additional subjects will receive the same dose of either 210 mg or 140 mg SC (in an allocation ratio of 1 AMG 557: 1 placebo).