CD40LG and major depressive disorder: ↑ IgM levels against LPS of P. aeruginosa and P. putida in MDD. ↑ The peak IgM, IgA and the total sum of all six IgM and IgA values in MDD. The symptom profiles of ↑ IgM and IgA were: fatigue, autonomic and gastro-intestinal symptoms, and subjective feeling of infection.