A Study to Assess Adverse Events, How the Drug Moves Through the Body and Effectiveness of Intravenous Infusions of ABBV-319 in Adult Participants With Systemic Lupus Erythematosus (SLE) and Sjogren's Disease (SjD)

Who May Qualify: - Systemic Lupus Erythematosus (SLE) Population - Clinical diagnosis of SLE at least 6 months prior to Screening as defined by the 2019 European Alliance of Associations for Rheumatology (EULAR)/American College Of Rheumatology (ACR) classification criteria for SLE and a positive antinuclear antibody (ANA) \>= 1:80 drawn at Screening. - SLE Population - Presence of anti-double stranded DNA (dsDNA), anti-Smith (Sm), anti-ribonucleoprotein (RNP), or anti-Sjogren's syndrome Ag A (SSA) Abs above the upper limit of normal (ULN). - Sjogren's Disease (SjD) Population - Primary diagnosis of SjD at least 6 months prior to Screening as defined by the ACR/EULAR 2016 Criteria. - SjD Population - EULAR Sjogren's Syndrome Disease Activity Index (ESSDAI) \>= 5 at Screening. - SjD Population - EULAR Sjogren's Syndrome Patient Reported Index (ESSPRI) \>= 5 at Screening. Who Should NOT Join This Trial: - History of infection as defined in the protocol. - Any of the medical diseases or disorders listed in the protocol. - History of clinically significant (per investigator's judgment) drug or alcohol abuse within the 6 months prior to Screening. - Any planned elective surgery that would impact study procedures or assessments through the completion of the Day 365 assessments. - Any clinically significant ECG abnormalities at Screening. Always talk to your doctor about whether this trial is right for you.