This study was approved by the ethics committee of Nara Medical University School of Medicine and was carried out in accordance with The Code of Ethics of the World Medical Association (Declaration of Helsinki) for experiments involving humans. All participants were given a complete description of the study and have provided written informed consent before enrollment.
2.1 Participants And Clinical Assessments
The participants included 29 ASD patients (age: 28.0 ± 6.7 years, 5 females) and 30 TD individuals (age: 27.2 ± 5.6 years, 5 females) of Japanese ethnicity. All participants have been born and have been living in Japan. ASD patients were recruited from the outpatient service of the Department of Psychiatry, Nara Medical University Hospital and its affiliated psychiatric clinic. ASD diagnosis was based on the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5) criteria. At least two experienced psychiatrists separately examined the patients, and a diagnostic consensus was reached. Further evaluation was performed using ADOS-2 by psychiatrists and trained staff (35). Autism symptom severity was assessed via self-report using the Autism Quotient-Japanese version (AQ-J)(36, 37). The full intelligence quotient (FIQ) of each participant was estimated using the Similarities and the Symbol search subtests of the Wechsler Adult Intelligence Scale, Third Edition (38). The following exclusion criteria were used: participants under 17 years old; those with low intelligence (FIQ < 70); those diagnosed with other neurological disorders and mental illnesses as evaluated by the Mini-International Neuropsychiatric Interview; and those who used steroids. We did not evaluate Asperger’s syndrome.
2.2 Monocyte Isolation And Macrophage Differentiation
We used a magnetic-activated cell sorting (MACS) system (Miltenyi Biotec, San Diego, CA, USA) for monocyte isolation, and subsequently we used Human M1 or M2 Macrophage Differentiation Kit (R & D Systems, Minneapolis, MN, USA) according to the manufacturer’s protocol. Briefly, whole human blood samples were collected through venipuncture from all participants during daytime (09:00–16:00) and were stored on ice. Immediately, PBMCs were separated from whole blood using density-gradient centrifugation with the separation medium Lymphoprep (Axis Shield, Oslo, Norway), separation tubes, and Leucosep (Greiner Bio-One, North Carolina, USA). CD14 + monocytes were isolated using the MACS system with CD14 microbeads (Miltenyi Biotec, Bergisch Gladbach, Germany) from PBMCs. These cells were used as monocytes.
For macrophage differentiation, CD14 + monocytes were resuspended in phosphate-buffered saline solution (Wako, Osaka, JAPAN), containing 0.5% bovine serum albumin (Sigma-Aldrich, St. Louis, MO, USA), 2 mM ethylenediaminetetraacetic acid, and 1% Penicillin-Streptomycin mixed solution (Nacalai Tesque, Kyoto, JAPAN). They were seeded at a density of 1 × 106 cells/mL onto M1 or M2 differentiation medium incubated with the recombinant human granulocyte-macrophage colony-stimulating factor (GM-CSF) or the recombinant human macrophage colony-stimulating factor (M-CSF), respectively at 37 °C in a humified atmosphere of 5% CO2. On day 3, half of each culture medium was replaced with a fresh medium, and the M1 or M2 macrophages were obtained on day 6.
2.3 Quantitative RT-PCR (qRT-PCR)
To measure the mRNA levels of cytokines (i.e., IL-1β, IL-6, TNF-α, IL-17RA, and IL-10) and C-C chemokine receptor type 7 (CCR7) in human M1 macrophages, M2 macrophages, and monocytes, total RNA was extracted from the cells using a Direct-Zol RNA miniprep kit (Zymo Research, Irvine, CA) according to the manufacturer’s protocol. RNA concentration was determined using the absorbance at 260 nm measured with a DU 730 spectrophotometer (Beckman Coulter Inc., Fullerton, CA, USA), and the concentration was standardized to be 30 ng/µL. First-strand cDNA was synthesized from the total RNA using an iScript kit (Bio-Rad Laboratories, Hercules, CA), and quantitative RT-PCR was performed using SYBR Premix Ex Taq II (Tli RNaseH Plus, TAKARA BIO INC., Otsu, Shiga, Japan) with a StepOne Plus real-time PCR system (Thermo Fisher Scientific Inc.). The normalization and the relative quantification of the expression levels of the target genes were performed using the ΔCT method, and the constitutively expressed genes β-actin (ACTB) and cyclophilin A (CyA) were used as internal controls. The mRNA expression ratios of M1/M2 macrophages were calculated by dividing the analyzed gene expression level within M1 macrophages by the same analyzed gene expression level within M2 macrophages. The primer sequences used were as follows: ACTB, forward 5′-GATGTGGATCAGCAAGCA-3′, reverse 5′-AGAAAGGGTGTAACGCAACTA-3′; CyA, forward 5′-GCAGACAAGGTCCCAAAG-3′, reverse 5′-GAAGTCACCACCCTGACAC-3′; IL-1β, forward 5′-CTGTCCTGCGTGTTGAAAGA-3′, reverse 5′-GAAGACAAATCGCTTTTCCA-3′; IL-6, forward
5′-AGTGAGGAACAAGCCAGAGC-3′, reverse 5′-CAGGGGTGGTTATTGCATCT-3′; TNF-α, forward 5′-GGCAGTCAGATCATCTTCTCG-3′, reverse 5′-CAGCTTGAGGGTTTGCTACA-3′; interleukin 17 receptor A (IL-17RA), forward 5′-GTTTTACCTTCAGCCACTTT-3′, reverse 5′-ATGGCGTGGTTACCTTCAT-3′; IL-10, forward 5′-GCCTAACATGCTTCGAGATC-3′, reverse 5′-TGATGTCTGGGTCTTGGTTC-3′; and CCR7, forward 5′-TTCAGTGGCATGCTCCTACTTC-3′, reverse 5′-GCTGAGACAGCCTGGACGAT-3′.
2.4 Statistical Analysis
Differences between the ASD patients and TD individuals in terms of demographic characteristics, i.e., age, educational level, and FIQ, were examined using Welch’s t-test, and Fisher's exact test was used to examine the differences in sex and allergic diseases. qRT-PCR data are presented as median values and interquartile ranges. Comparisons were performed using the Mann-Whitney U test. RNA concentration data were presented as the mean and standard error of the mean. The comparison was performed using one-way analysis of variance. Positive likelihood ratios (PLRs) were used to evaluate the ability of cytokine expression in M1 and M2 macrophages in predicting ASD diagnosis. The PLR is one of the best methods to evaluate diagnostic accuracy and gives the change in the odds of having a diagnosis in patients with a positive test (39). A PLR of 10 indicates a 10-fold increase in the odds of a particular condition in a patient with a positive test result. Normally, PLRs of greater than 10 significantly increase the probability of a disease (40). The PLR is calculated as sensitivity/(1 – specificity) through the receiver operating characteristic (ROC) curves. Correlation analyses between gene expression levels and age, FIQ, and the severity of ASD symptoms were performed using Spearman’s rank correlation. Logistic regression analysis was used to examine the association between TNF-α mRNA expression in macrophages and the prevalence of allergic diseases. All statistical analyses were performed using Prism 8 (GraphPad), except for logistic regression analysis, which was performed using SPSS version 26 (IBM). P-values < 0.05 were considered statistically significant and are indicated in the figures as *p < 0.05, **p < 0.01, ***p < 0.001, and ****p < 0.0001.