Reduction of CD21hiCD23low marginal zone B (MZB) cells among splenic B220+ B cells (Figure S17, Supporting Information) suggested the depletion of DLL1‐dependent MZB cells, confirming the efficacy of the DLL1 antibody in vivo.[29] As expected, lupus mice treated with DLL1 antibody presented a lower incidence of cutaneous lupus (Figure 7E) and reduced sizes and weights of lymph nodes (exemplified by renal draining, cervical and axillary lymph nodes (Figure 7F). Here, DLL1 is linked to systemic lupus erythematosus.