Background <p>Systemic lupus erythematosus (SLE) is a complex autoimmune disease where B-cell proliferation and activation play a pivotal role in pathogenesis. While the role of basophils in SLE is recognized, the impact of basophil-derived exosomes on B-cell proliferation and activation has not been thoroughly investigated.</p> Methods <p>Exosomes from human basophils in both resting and activated states were isolated and characterized. These exosomes were then co-cultured with B cells to assess their effects on B-cell survival and proliferation. To investigate the in vivo roles, a Pristane-induced lupus model in <i>Mcpt8</i>^{<i>flox/flox CAGGCre−</i>}^<i>ERTM</i>&#xa0;mice was utilized. The Pristane-<i>Mcpt8</i>^{<i>flox/flox, CAGGCre−ERTM</i>} mice were analyzed for basophil-derived exosome accumulation in the spleen and kidneys, and the effects on immune cell proliferation and plasma cell-plasmablast balance were assessed. Transcriptomic analysis was conducted on basophil-derived exosomes to identify key non-coding RNAs. Lupus mice were humanized by transplanting peripheral blood mononuclear cells (PBMCs) from patients with SLE into immunodeficient mice to evaluate the effects of intervening miR-24550 in B cells.</p> Results <p>Activated basophil-derived exosomes were found to enhance B-cell survival and proliferation in patients with SLE. In the lupus mouse model, basophil-derived exosomes accumulated primarily in the spleen and kidneys, inducing excessive immune cell proliferation and disrupting the plasma cell-plasmablast balance, which worsened kidney damage. Transcriptomic analysis revealed key non-coding RNAs within basophil-derived exosomes. Activated basophil-derived exosomes were internalized by B cells, releasing miR-24550, which promoted B-cell proliferation. In humanized SLE mice, inhibiting miR-24550 in B cells reduced immune hyperactivation and improved renal function, similar to the effects of inhibiting basophil-derived exosomes release in Pristane-<i>Mcpt8</i>^{<i>flox/flox, CAGGCre−ERTM</i>}&#xa0;mice. Ultimately, basophil-derived exosomal miR-24550 promotes B-cell proliferation and activation by targeting Krüppel-like factor 5 (KLF5), which exacerbates SLE progression.</p> Conclusions <p>Basophil-derived exosomal miR-24550 promotes B-cell proliferation and activation by targeting KLF5, thereby exacerbating SLE progression. This study presents a novel strategy for SLE prevention and treatment.</p> Graphical Abstract <p></p>