VIRAL SAFETY OF BLOOD DERIVATIVES BY IMMUNE NEUTRALIZATION

Despite careful oner selection and virus inactivation procedures, tran smission of viruses by transfusion of blood and blood derivatives is s till a threat. Outbreaks of hepatitis A among hemophiliacs Raving rece ived highly purified, immune globulin depleted coagulation factor conc entrates, put the importance of immune neutralization of viruses in bl ood derivatives in focus. Neutralizing antibodies may block several st eps in the virus infection of a cell, from binding of virus to the cel lular receptor to the uncoating of virus after uptake in the cell, The efficacy of antibody neutralizing activity depends on the availabilit y and stability of the neutralizing epitopes. Hepatitis A and B viruse s are very efficiently neutralized by antibodies and immune escape mut ants rarely emerge. Anti-parvovirus B19 antibodies do not fully inacti vate the virus, at least in low concentrations, but may prevent develo pment of disease. The neutralizing epitopes on hepatitis C virus and h uman immunodeficiency virus are located on hypervariable regions of vi rus membrane proteins. The effects of neutralizing antibodies are thus marginal as immune escape mutants emerge at a relatively high frequen cy for both viruses. The neutralizing activity of anti-cytomegalovirus antibodies is also questionable as persons may become reinfected with cytomegolvirus despite high levels of antibodies. Plasma and plasma d erivatives produced from large donor pools have the potential of being very efficient transmitters of viruses, Neutralizing antibodies are N ature's own, and very important barriers against the spread of many kn own and unknown viruses contaminating the plasma pools.