CRP and major depressive disorder: In addition, although observational studies have consistently reported elevated CRP and IL-6 levels in depression and schizophrenia (Goldsmith et al., 2016; Haapakoski et al., 2015; Miller et al., 2011; Upthegrove et al., 2014), MR analysis has reported a protective effect of CRP for schizophrenia (Hartwig et al., 2017).