〔Abstract〕 Objective To explore the impacts and fundamental mechanisms of the PU.1 inhibitor DB2313 on the immune function in MRL/lpr mice. Methods A total of thirty MRL/lpr lupus mice were randomly distributed into three separate groups: the model control group, the PU.1 inhibitor DB2313 treatment group(administered at a dose of 17 mg/kg), and the positive drug control Telitacicept(TACI-Ig) group(administered at a dose of 7.5 mg/kg). Furthermore, a group of ten BALB/c mice were assigned as the normal group. The DB2313 administration group was treated with intraperitoneal injections of the drug on three occasions per week, while the TACI-Ig group received subcutaneous injections every second day; both treatment protocols were maintained for a duration of five weeks. Both the control group and the model group were administered intraperitoneal injections of a volume of saline that was equivalent across groups. After the drug was given, mice were sacrificed by dislocation after orbital vein blood collection. The thymus and spleen were aseptically excised, individually weighed, and subsequently utilized to compute the thymus index and spleen index. The relative distribution of T lymphocyte subsets within the spleen was ascertained through flow cytometry. Serum concentrations of anti-nuclear antibodies(ANA) and anti-double-stranded DNA antibodies were quantified using an enzyme-linked immunosorbent assay(ELISA). The levels of inflammatory factors interleukin-6(IL-6),tumor necrosis factor-α(TNF-α),interferon-γ(IFN-γ) were measured by CBA method. Hematoxylin and eosin(HE) staining was employed to examine pathological alterations in the spleen. The expression of PU.1 and IL-9 in spleen tissue was detected using immunohistochemistry. Additionally, the expression level of PU.1 protein in the spleen tissue was ascertained through Western blot analysis. Results The administration of DB2313 significantly ameliorated spleen lesions in MRL/lpr mice and decreased the levels of anti-ds-DNA, ANA, TNF-α, IL-6, and IFN-γ. It also reduced the proportion of total T cells, TFH cells, Th17 cells, and Th9 cells in the mouse spleen, while increasing the proportion of Treg cells. Furthermore, it lowered the level of PU.1 protein in the spleen. Immunohistochemistry results demonstrated that DB2313 treatment significantly diminished the expression of PU.1 and IL-9 in spleen tissue. Conclusion The PU.1 inhibitor DB2313 can improve spleen lesions in MRL/lpr mice and slow the progression of the disease, and its mechanism is related to the regulation of immune cell functions.