CTLA4 and obesity due to melanocortin 4 receptor deficiency: Bifidobacterium pseudolongum enhances antitumor immunity (Mager et al., 2020), exerts an anti-influenza effect (Zhang et al., 2020), enhances the efficacy of anti-CTLA4 treatment (Research, A. A for C. 2020), and treated obesity (Bo et al., 2020) in an animal model, which inspired us to explore its mechanism from the perspectives of immunity and metabolism.