Studies reporting that depression is accompanied by activation of immune–inflammatory pathways [35] with increased IgM/IgA responses to lipopolysaccharides (LPS) from gram-negative commensal bacteria, indicate that at least in part adverse mood is supported by commensal microbes and or metabolite translocations across the intestinal epithelial barrier [32,33]. The gene discussed is CD40LG; the disease is major depressive disorder.