Immunobiology of persistent blood-borne viral infections.

Host-virus interactions have co-evolved to play an interactive role in the pathogenesis of viral infections and their disease outcome. Host responses to viral infections, including the cell-mediated and humoral immune responses, have been a subject of intensive research in virology and immunology. Definition of specific cellular receptors for cellular entry of the agents, the rates of their intracellular viral replication, the rates of turnover of circulating virions, persistence of viral infection possibly due to inadequate immune responses, and continued formation of circulating immune complexes provide the framework for our current understanding of the immunopathology of virally induced disease. Among the multiple blood-borne viruses (BBV) transmissible through transfusion, hepatitis B virus (HBV), hepatitis C virus (HCV), and human immunodeficiency viruses (HIV-1/-2) are relatively more important than several other viruses. Not only do they establish asymptomatic persistent infections with occasional oncogenic sequelae, but they also cause significant morbidity and mortality when transmitted through transfusion of blood and blood products. Molecular characterization of these agents and their in vitro inactivation and removal from blood have become key issues in contemporary transfusion safety since the advent of AIDS. Because many of the BBV are associated with white blood cells that have no therapeutic benefit in haemotherapy, simple filtration-removal of leukocytes from donated blood confers a dual benefit of immunological and virological safety in transfusion medicine.