Expression and detection of anti-HBs antibodies after hepatitis B virus infection or vaccination in the context of protective immunity.

Anti-HBs antibodies develop after natural infection with hepatitis B virus (HBV) or vaccination against this virus, as a result of activation of the human immune system by the HBV surface antigen (HBsAg). Anti-HBs-positive individuals are immunologically competent against HBV infection. This immunity is determined by the antibody levels in the bloodstream after resolution of natural infection or after vaccination. Anti-HBs antibody levels have been observed to decrease to below the protective level years after natural infection or vaccination, and there is reason to doubt that protective immunity to HBV is maintained after that. Factors that affect the maintenance of the anti-HBs antibody level in the bloodstream have been reported. Maintenance of immunity to HBV has been reported in anti-HBs negative individuals and those with detectable but low levels after natural infection or after vaccination. On the other hand, detection of anti-HBs antibodies without protective activity has also been observed. The presence or absence of anti-HBs antibodies in the context of HBV immunity has been the subject of extensive discussion and clinical, laboratory and epidemiological interest. These three scenarios of the anti-HBs response are discussed in this review article.