Introduction: There has long been a need for diagnostic, theragnostic, and prognostic
biomarkers for psychiatric disorders. Biomarkers help in reducing ambiguity and arbitrariness and
increase objectivity. In this context, many candidates for hormonal, immunological, serological, and
neuroimaging markers have been proposed, but none of these marker candidates alone nor a biomarker
panel has been approved for any disease. The fact that almost all psychiatric disorders are
heterogeneous makes this process challenging. However, strong biomarker candidates have been
identified, especially in light of the large number of clinical and preclinical studies conducted within
the last five years.
Objective: The aim of this article was to compile and discuss the current information on immune
biomarkers in major psychiatric disorders, such as schizophrenia, depression, bipolar disorder, and
Methods: In this study, respected scientific databases were searched using key terms related to the
subject, and the related literature was examined in detail.
Results: There are many relationships between psychiatric disorders and immune system parameters.
Evidence also suggests that neuroinflammation is involved in the etiopathogenesis of psychiatric
disorders. Markers, such as proinflammatory cytokines, tumor necrosis factor alpha, and C-reactive
protein have been associated with psychiatric disorders in numerous studies.
Conclusions: The neuroinflammation hypothesis has an important place in the etiopathogenesis of
psychiatric disorders. Uncertainty remains as to whether neuroinflammation is a cause or consequence
of psychiatric disorders. Some researchers have indicated that intestinal microbiota composition
disorders and dysbiosis are sources of neuroinflammation. Immune marker studies are of
great importance in terms of eliminating this uncertainty and overcoming diagnostic and treatment
difficulties in the clinic. In this review, biomarker studies on psychiatric disorders were examined
from the viewpoint of the immune system and discussed in light of the current studies.