This study consists of a randomized, double-blind, placebo-controlled Phase Ia part and an open-label Phase Ib part. The Phase Ia part is a single ascending-dose study of subcutaneous QLS2404 Injection in healthy participants, designed to evaluate the safety and tolerability of QLS2404 Injection in healthy participants. The Phase Ib part is a multiple ascending-dose study of subcutaneous QLS2404 Injection in participants with systemic lupus erythematosus and primary Sjögren's syndrome, designed to evaluate the safety, tolerability, pharmacokinetics, pharmacodynamics, and preliminary efficacy of QLS2404 Injection.