C8B encodes the beta chain of complement component C8, a critical structural component of the membrane attack complex (MAC) 1. C8B associates with C8A and C8G to form the C8 heterotrimer, which functions as a non-covalently bound complex in serum 2. During complement activation through classical, alternative, lectin, and GZMK pathways, C8B participates in MAC assembly by associating with C5b, C6, and C7 to form the C5b8 intermediate complex 3. This complex inserts into target cell membranes and traverses the lipid bilayer, increasing membrane rigidity and facilitating pore formation that leads to cell lysis 3. Notably, C8B does not independently form pores but contributes essential structural components to the functional MAC 3. C8B is located on chromosome 1 within a linked cluster with C8A, spanning approximately 40 kb with 12 exons 2. Disease associations include complement component C8 deficiency; genetic variations in C8B (p.Thr542Ile) combined with C2 mutations impair complement pathway activation and neutrophil/monocyte function 4. Reduced C8B expression correlates with complement pathway dysregulation in hypermobile Ehlers-Danlos syndrome 5 and intrahepatic cholangiocarcinoma 6. Elevated plasma C8B levels show potential as a biomarker for acute myocardial infarction diagnosis 7.