Foxo1 knocked down but not control lentivirus infection induced CD19‐deficient MZP cells (CD21hiIgMhiCD1dhiCD23+IgDhi) to produce MZ B cells (CD21hiIgMhiCD1dhiCD23−IgDlo) (Fig. 6D, E and Fig. S7). Here, CD19 is linked to lentivirus infection.