C8A encodes the alpha chain of complement component C8, a critical structural component of the membrane attack complex (MAC). C8A functions as part of a tripartite complex with C8B and C8G; together these chains insert into target cell membranes to form cytolytic pores 12. During MAC assembly, C8A associates with C5b, C6, and C7 to form the C5b-8 intermediate complex that inserts into target membranes and increases membrane rigidity, ultimately leading to cell lysis 2. The complement cascade containing C8A can be activated through classical, alternative, lectin, and GZMK pathways, culminating in pathogen destruction and adaptive immune strengthening 12. C8A dysregulation associates with multiple disease states. C8A deficiency causes direct complement component 8 deficiency. Reduced C8A expression occurs in hypermobile Ehlers-Danlos syndrome (hEDS), where complement pathway attenuation contributes to systemic immune dysregulation 3. In breast cancer, C8A mRNA expression is prognostic of disease-free survival and predictive of trastuzumab treatment benefit, with high C8A expression correlating with improved outcomes 4. Rare deleterious C8A variants occur in childhood-onset systemic lupus erythematosus patients, suggesting involvement in monogenic autoimmune disease 5. Cholangiocarcinoma pathogenesis involves C8A downregulation through three-dimensional genome rearrangements 6.