Neuroimmune Dysregulation and Synaptic Pruning in Autism Spectrum Disorder

Autism spectrum disorder (ASD) is a neurodevelopmental condition characterized by social communication deficits and repetitive behaviors, now affecting approximately 1 in 31 children. While traditionally defined behaviorally, ASD is increasingly understood as a disorder of brain connectivity arising from altered synaptic formation and refinement. This narrative review synthesizes evidence on neuroimmune dysregulation in ASD, focusing on immune-mediated synaptic pruning mechanisms. We conducted a comprehensive literature search in PubMed, Scopus, and Web of Science (2010–2026), prioritizing high-impact peer-reviewed research. Convergent findings suggest that the classical complement cascade (C1q-C3) tags specific synapses for elimination, while microglia participate in the phagocytic removal of tagged connections. Genetic studies have reported associations between ASD and variants in complement-related genes (C1q, C3, CR3, and C4A, although the strongest evidence for C4A-mediated pruning comes from schizophrenia research), as well as in microglial function genes (TREM2, PTEN, SHANK3). Neuroimaging reveals a dynamic pattern of local hyperconnectivity transitioning to long-range hypoconnectivity during development, particularly affecting prefrontal, insular, and cerebellar regions. Systemic inflammation, including gut–brain axis dysbiosis and maternal immune activation, may amplify neuroimmune dysregulation. We conclude that ASD can be understood, in part, as a disorder of synaptic immunology, where disrupted neuroimmune communication during critical developmental windows may contribute to altered connectivity. The complement–microglia axis therefore represents a potential mechanistic target for future therapeutic investigation.