injected into CD19‐deficient mice, the CD19 expression but not control lentivirus infection induced CD19‐deficient MZP (CD21hiIgMhiCD1dhiCD23+IgDhi) to produce MZ B cells (CD21hiIgMhiCD1dhiCD23−IgDlo) (Fig. 3E, F and Fig. S2). Here, CD19 is linked to lentivirus infection.