Autoantibodies to Fe2+ Hb and Fe3+ Hb exhibited high penetrance in lupus-prone mice (Figure 2E; Figure S3 in Supplementary Material), with a predominance of the IgM isotype in sera and of the IgM and IgG2a isotypes in organ eluates (Figure 2F). The gene discussed is CD40LG; the disease is systemic lupus erythematosus.