Inclusion Criteria:

• Age \> 18 years old.
• SLE with ≥ 4 of eleven diagnostic criteria approved by the American College of Rheumatology
• Stable immunosuppressants (MMF ≤ 3 g/day, azathioprine ≤ 100 mg/day; methotrexate ≤ 15 mg/day) and/or antimalarials (hydroxychloroquine ≤ 400 mg/day) for 30 days prior to screening; stable oral corticosteroids for 2 weeks prior to screening; ≤ 20 mg/day prednisone or equivalent; stable belimumab for 90 days prior to screening;
• BILAG 2004 index level A disease activity in ≥ 1 organ/system except renal or central nervous system or (ii) BILAG 2004 index level B disease activity in ≥ 2 organs/systems if no level A disease activity is present and (iii) SLEDAI ≥ 6;

Exclusion Criteria:

• Acute flare of SLE threatening vital organs and requiring intravenous
• Pregnant or lactating
• Moderately serious or serious comorbidities (e.g., diabetes mellitus, congestive heart failure, chronic obstructive pulmonary disease, chronic renal insufficiency)
• Patients receiving cyclophosphamide within 3 months
• Active chronic infections (e.g., HIV, hepatitis B virus, hepatitis C virus, mycobacteria); patient with oral steroid-dependent asthma;
• Infections requiring intravenous antibiotics within a month or oral antibiotics within two weeks of screening; Patients taking (unwilling or unable to stop) NAC or other antioxidants within 1 month of screening
• Patients who participated in the pilot RCT or are taking daily acetaminophen (\</= 1 g/day PRN is allowed if documented)
• Patients receiving rituximab within 12 months or other biologic therapy within five half-lives
• Patients receiving mTOR inhibitors (rapamycin/sirolimus, everolimus)
• Patients enrolled in other interventional trials
• Healthy subjects serve as controls for in vitro immunological studies