In this study, unlike the pathogenic role of IgG antibodies in the context of obesity observed by Winer et al. [21], IgM was required for B-1 cells to suppress metabolic disease in DIO mice, since secretory IgM (sIgM)-deficient B-1 cells lost their suppressive capacity [28]. Here, CD40LG is linked to obesity due to melanocortin 4 receptor deficiency.