Comparing the serum IgM/IgA responses directed to the LPS of six Gram-negative bacteria and the IgG responses to oxidized LDL (oxLDL) in 29 BP1 patients, 37 BP2, 44 MDD and 30 healthy individuals it was found that MDD, BP1 and BP2 are accompanied by an immune response due to increased LPS load, while these aberrations in the gut–brain axis are more pronounced in BP1 and melancholia. The gene discussed is CD79A; the disease is major depressive disorder.