CRP and major depressive disorder: The immune imbalances associated with depression may already begin to emerge during adolescence, with increases in interleukin (IL)-6 and C-Reactive Protein (CRP) being most robust indicators of depressive symptoms, although meta-analytic studies show large differences in outcomes and effects sizes between studies and immune measures (Colasanto et al., 2020; D'Acunto et al., 2019; Toenders et al., 2021).