Circulating capsid-antibody-complexes (CACs) drive intrahepatic complement deposition and inform subclinical liver...

Chronic infection with Hepatitis B Virus (HBV) often results in a dysfunctional virus-specific T cell response hampering viral clearance. Paradoxically, intrahepatic inflammatory responses that contribute more to liver histopathology than to viral suppression are commonly observed, which are widely believed to be cell mediated. The involvement of humoral immunity in this process however is not well documented. To investigate the possible roles of HBV Capsid-Antibody Complexes (CACs) in eliciting chronic liver inflammation, we developed a novel microplate-based assay for the quantification of CACs in serum. The CACs assay showed high sensitivity and specificity with its readout closely correlating with the molecular features of CACs. A cross-sectional study on untreated chronic hepatitis B (CHB) patients showed a 77% positive rate for CACs with significant association with alanine transaminase (ALT), intrahepatic inflammation, and complement deposition, suggestive of its functional role in hepatic injury. Multiple staining of complement activation fragment C4d with major leukocyte and myofibroblast markers revealed an intertwined picture in periportal area with a morphology reminiscent of "piecemeal necrosis". In a pooled cohort with ALT levels lower than 40 IU/ml, CACs alone revealed subclinical liver inflammation. We provide definitive evidence for a causative role for CACs in complement-mediated intrahepatic immunopathology, an additional mechanism contributing to liver damage in CHB. Assessment of CACs in serum complements current clinical markers for assessing CHB associated inflammation.