The significant differences in IL-4 levels, which were 27.4 times higher in Bangladeshi MDD patients compared to Chinese MDD patients, and in the fold increase in MDD patients relative to controls, which were 16.5 times higher in Bangladeshi controls compared to Chinese control subjects, may have been caused by differences in the study subjects, biases in the detection methods, or racial and ethnic differences between the Chinese and Bangladeshi populations. This evidence concerns the gene IL4 and major depressive disorder.