Comparison of peripheral blood TLR mRNA levels in patients diagnosed with Autism Spectrum Disorder and healthy controls

Autism Spectrum Disorder (ASD) is a neurodevelopmental disorder in which multiple factors play a role in its etiology, and no single factor can be identified as the cause. In the etiology, genetic, environmental, and neurobiological factors are effective, and it has also been demonstrated in the literature that neuroinflammation and components of the immune system play a role. Toll-Like Receptors (TLRs), which are pattern recognition receptors in the immune system, not only function as receptors but also to influence dynamic processes in the central nervous system, including neurogenesis, axonal growth, and plasticity through TLR signaling. In recent years, TLRs have become a subject of research in neuropsychiatric disorders; however, studies on TLRs in ASD appear to be limited. In order to investigate the role of TLRs in the etiopathogenesis of ASD, TLR mRNA expression and serum protein levels were analyzed in the peripheral blood of 31 ASD patients and 31 healthy control children and adolescents. The case group consisted of children and adolescents aged 4-18 years who were diagnosed with ASD according to the DSM-V criteria, had no known chronic systemic diseases, and not receiving any medical treatment. The control group consisted of healthy children and adolescents without psychiatric disorders or known chronic systemic diseases, also not receiving any medical treatment, and had a similar age and gender distribution to the case group. A clinical interview based on DSM-V was conducted with the participants and their parents, and the Childhood Autism Rating Scale and Aberrant Behavior Checklist were applied. The TLR mRNA expression levels in the peripheral blood of the participants were compared using RT-qPCR, and the serum TLR protein levels of the differentially expressed TLR types were measured by the ELISA method. As a result, our study revealed that the TLR1, TLR4, TLR5, and TLR8 mRNA expression and protein levels were higher in the ASD group compared to the control group, while the TLR6 mRNA expression and protein levels were lower. No significant differences were observed in the mRNA expression levels of TLR2, TLR3, TLR7, TLR9, and TLR10. The higher mRNA expression and protein levels of TLR4 in the ASD group are consistent with the literature; however, to the best of our knowledge, no previous studies have analyzed the expression and protein levels of TLR1, TLR5, TLR6, and TLR8 in ASD, our findings represent the first report of these results in the literature. A better understanding of TLR signaling in ASD may shed light on the etiology of ASD and contribute to the development of future therapeutic strategies. Furthermore, TLRs could serve as potential biomarkers for the diagnosis of ASD. Our findings may be considered as a preliminary study for future research aimed at exploring the potential role of TLRs in the etiopathogenesis of ASD. Keywords: Autism Spectrum Disorder, Toll-Like Receptors, Child and Adolescent