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.