• Male or female aged 8 to \< 21 years;

• Must meet Classification Criteria for SLE as per the criteria of the American College of Rheumatology (ACR)/ European League Against Rheumatism

• Diagnosed with proliferative LN as per the International Society of Nephrology/Renal Pathology Society4 based on kidney biopsy done within 90 days prior to enrollment into the study;

• Subjects may have been previously diagnosed with LN. For study inclusion, the kidney biopsy must be interpreted as one of the following classes: Class 3, Class 3/5, Class 4, or Class 4/5.

• Treatment of LN with twice daily MMF as per the decision of the treating physician.

• The subject will have taken MMF as prescribed by their treating physician for a minimum of 4 days (or 8 doses).

• Subject tolerates MMF as per the treating physician's opinion;

• Able to swallow MMF tablets and capsules;

• If subject is treated with belimumab, must be IV or SQ;

• Subjects who are willing and able to comply with scheduled visits, treatment plan, laboratory tests, and other study procedures;

• Evidence of a personally signed and dated Informed Consent document and Assent document (as appropriate) indicating that the subject and a legally acceptable representative/ parent(s)/legal guardian has been informed of all pertinent aspects of the study.

⁃ Parent or legal guardian must have a smart phone available and able to support the PLUMM smart phone application.

⁃ Must be able to complete study questionnaires in English or Spanish.