IL6 and major depressive disorder: This is similar to MR findings for coronary heart disease, where IL-6 but not CRP have been shown to play a potential causal role [92, 93].Studies on a broader range of immune markers (e.g. cytokines, immune cells) and specific immune pathways may be more useful to understand the role of inflammation in depression, rather than CRP which is a non-specific marker of systemic immune activation [94].