Autoimmunity and expansion of B1b cells requires Itch^−/− T cells.(A) Rag1^−/− mice were reconstituted with combinations of bone marrow from WT or Itch^−/− mouse strains (Table 1) and analyzed 14 to 18 weeks later. Anti-IgM and anti-IgE ELISA are shown for sera of mixed chimeras. (B) Representative FACS plots of peritoneal cells from mixed chimeric mice are shown for B cells after gating on lymphocytes using side and forward scatter profiles. (C) B1-gated peritoneal cells from the same mice were stained for B1a (Mac1⁺CD5⁺) and B1b (Mac1⁺CD5⁻) cells. (D) Rag1^−/− mice were reconstituted with WT or Itch^−/− purified peritoneal B1 cells together with purified Itch^−/− or WT CD4⁺ T cells (LN), as indicated. Sera were analyzed 4 weeks later for total IgM (left) and IgE (right) by ELISA. (*P < .05). (E) Rag1^−/− mice were reconstituted with WT or Itch^−/− B cells (LN) together with purified Itch^−/− or WT CD4⁺ T cells, as indicated. Sera were analyzed 4 weeks later for IgE by ELISA.