Table 2.

Included articles and their study design

Publication	Study design	Country	Clinical scales	Investigation
Author, year				Medium	Markers
A. Immunoglobulins
Kanchanatawan et al. 2017 [40]	Observational cross-sectional with healthy controls	Thailand	DSM IV, FF, PANSS, SANS, SDS, HAM-D, HAM-A, CANTAB	Blood	3HK, KYNA, QUIN, AA, XA, PA, and IgA and IgM responses to these six TRYCATs
Kanchanatawan et al. 2018a [41]	Observational cross-sectional with healthy controls	Thailand	DSM-IV-TR, Thai version of MINI, SDS, SANS, PANSS, BPRS	Blood	3HK, KA, QUIN, AA, XA, PA, and IgA and IgM responses to these six TRYCATs
Kanchanatawan et al. 2018b [42]	Observational cross-sectional with healthy controls	Thailand	DSM-IV, SDS, SANS, PANSS, BPRS	Blood	3HK, KYNA, QUIN, AA, XA, PA, and IgA responses to these six TRYCATs
Bechter et al. 2010 [43]	Observational cross-sectional with healthy controls	Germany	ICD-10	Blood and CSF	KYN, Trp, albumin, IgG, IgA, IgM, oligoclonal IgG
B. Interleukins
Szymona et al. 2017 [44]	Observational prospective case-control study	Poland	ICD-10 (F20), SAPS, SANS, PANSS	Blood	KYNA, 3-HK, sIL-2R, IFN-α, IL-4
Barry et al. 2009 [45]	Observational cross-sectional with healthy controls	Ireland	DSM-IV, SCID-I for DSM-IV, SAPS, SANS, CDSS	Blood	L-Trp, KYN, 3HK, KYNA, 3-hydroxy-anthranilic acid, XA and 3-nitro-l-tyrosine
Kim et al. 2009 [46]	Observational prospective case-control study	Korea	DSM IV, PANSS	Blood	Trp and KYN as well as IL-2, IL-4, IL-6, TNF-α, IFN-γ, TGF-β1
Schwieler et al. 2015 [47]	Observational cross-sectional with healthy controls	Sweden	DSM­IV, BPRS, GAF	CSF	Cytokines: IL­1β, IL­2, IL­4, IL­6, IL­8, IL­10, IL­18, TNF­α, IFN­α­2a, and IFN­γ as well as KYNA, KYN, and Trp
				Human astrocyte culture	Effects of IL-6 on KYN and KYNA
Kegel et al. 2017 [48]	Observational cross-sectional with healthy control twins	Sweden	SCID-I, SCID-II, SANS, SAPS, SPQ-B, HAM-D, YMRS, GAF	CSF	KYNA, QUIN, Trp, IL-6, IL-8, TNF-α, albumin
				Blood	CRP and albumin
C. C-reactive protein
Wurfel et al. 2017 [49]	Observational cross-sectional with healthy controls	USA	DSM-IV, HAM-D, YMRS, BPRS version 4.0, CORE assessment of psychomotor change	Blood	High-sensitivity CRP, Trp, KYN, KYNA, 3HK

Abbreviations: 3HK 3-OH-kynurenine, AA anthranilic acid, Af affective disorder, BPRS The Brief Psychiatric Rating Scale, CANTAB The Cambridge Neuropsychological Test Automated Battery, CDSS Calgary Depression Scale for Schizophrenia, CRP C-reactive protein, CSF cerebrospinal fluid, DSM-IV-TR Diagnostic and Statistical Manual of Mental Disorders-Text Revision, DZ dizygotic twins, FF Fibromyalgia and Chronic Fatigue Syndrome Rating Scale, GAF Global Assessment of Functioning Scale, HAM-A Hamilton Anxiety Rating Scale, HAM-D Hamilton Depression Rating Scale, ICD 10 The International Classification of Diseases Tenth Edition, IFN- interferon-, Ig immunoglobulin, IL- interleukin-, KYN kynurenine, KYNA kynurenic acid, MDD major depressive disorder, MINI Mini-International Neuropsychiatric Interview, MZ monozygotic twins, ND not determined, PA picolinic acid, PANSS The Positive and Negative Syndrome Scale, QUIN quinolinic acid, SANS Scale for the Assessment of Negative Symptoms, SAPS Scale for the Assessment of Positive Symptoms, SCID-I/II for DSM-IV Structured Clinical Interview for Diagnostic and Statistical Manual IV Axis I/II Disorders, SDS Schedule for Deficit Syndrome, sIL-2R soluble interleukin-2 receptor, SPQ-B Schizotypal Personality Questionnaire Brief, Sz schizophrenia, SzA schizo-affective disorder, TGF- transforming growth factor, TNF­α tumor necrosis factor­α, Trp Tryptophan, TRYCATs tryptophan catabolites, XA xanthurenic acid, YMRS The Young Mania Rating Scale