Safety Study of AMG 811 in Subjects With Systemic Lupus Erythematosus With and Without Glomerulonephritis

Inclusion Criteria: * Men and women, between the ages of 18 and 70 years of age; * Body mass index from 18 to 40 kg/m2 \[Body Weight (kg)/Height2 (m2)\] at screening; * Diagnosis of SLE at least 6 months before randomization, including a positive antinuclear antibodies (ANA) during screening; if screening ANA is negative, documented historical ANA with a titer of at least 1:80 will be acceptable; * Any concurrent SLE pharmacologic regimen (including mycophenolate mofetil, azathioprine, leflunomide, methotrexate, and anti-malarials) must be stable for at least 30 days before randomization; * Prednisone ≤ 20 mg/day (or equivalent) is permitted; one increase or one decrease of ≤ 5 mg/day prednisone equivalent will be allowed within 30 days before randomization; Additional inclusion criteria for Part B: \- Active SLE with GN with no other apparent cause, defined by the following: Renal biopsy evidence (within 18 months) of nephritis using the WHO or International Society of Nephrology (ISN)/Renal Pathology Society (RPS) classification of SLE with GN (Class III or IV); Urine protein/creatinine ratio (UP/Cr) \> 1 or 24 hour urine protein \> 1g after at least 12 weeks of treatment with mycophenolate mofetil (at least 1.5 grams/day) or azathioprine (at least 100 mg orally per day); Superimposed membranous changes are allowed for those with Class III or Class IV SLE with GN; \- Prednisone ≤ 20 mg/day (or equivalent) at the time of randomization. Exclusion Criteria: * Any disorder (including psychiatric), condition or clinically significant disease (other than a diagnosis of SLE) that would, by its progressive nature and/or severity, interfere with the study evaluation, completion and/or procedures per the investigator's discretion; * Creatinine clearance within the screening period of less than 50 mL/min as calculated by the Cockcroft-Gault method * Signs or symptoms of a viral, bacterial or fungal infection within 30 days of study randomization, or recent history of repeated infections; * Underlying condition other than SLE or being on allowed immunosuppressants that predisposes one to infections * Prior use of the following agents: * Administration of an investigational biologic agent that primarily targets the immune system * Administration of cyclosporine, tacrolimus, sirolimus, IV immunoglobulin, and/or plasmapheresis within 3 months of randomization; * Administration of oral or IV cyclophosphamide (or any other alkylating agent) within 12 months (Part A) or 3 months (Part B) of randomization; * History of ethanol or drug abuse within the last one year prior to randomization; Additional exclusion criteria for Part B: * Rapidly progressive GN (defined as a doubling of serum creatinine within the past 3 months); * Evidence of significant chronicity, defined as: \> 50% glomeruli with sclerosis or \> 50% interstitial fibrosis on renal biopsy; or International Society of Nephrology (ISN)/Renal Pathology Society (RPS) 2003 Class III (C), IV-S (C) or IV-G (C).