Despite careful donor selection and virus inactivation procedures, transmission of viruses by transfusion of blood and blood derivatives is still a threat. Outbreaks of hepatitis A among hemophiliacs having received highly purified, immune globulin depleted coagulation factor concentrates, put the importance of immune neutralization of viruses in blood derivatives in focus. Neutralizing antibodies may block several steps in the virus infection of a cell, from binding of virus to the cellular receptor to the uncoating of virus after uptake in the cell. The efficacy of antibody neutralizing activity depends on the availability and stability of the neutralizing epitopes. Hepatitis A and B viruses are very efficiently neutralized by antibodies and immune escape mutants rarely emerge. Anti-parvovirus B19 antibodies do not fully inactivate the virus, at least in low concentrations, but may prevent development of disease. The neutralizing epitopes on hepatitis C virus and human immunodeficiency virus are located on hypervariable regions of virus membrane proteins. The effects of neutralizing antibodies are thus marginal as immune escape mutants emerge at a relatively high frequency 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 derivatives produced from large donor pools have the potential of being very efficient transmitters of viruses. Neutralizing antibodies are Nature's own, and very important barriers against the spread of many known and unknown viruses contaminating the plasma pools.
The localization of individually specific antigenic determinants on the monoclonal γM Mö was studied in gel diffusion experiments with 19S γM Mö and its 7S subunit. Various types of such determinants were delineated. Some were demonstrable both on the intact macroglobulin molecule and on the subunit. The latter was often unable to precipitate with the corresponding antibody, but combined with it and inhibited precipitation. Immunization of rabbits with purified γMs Mö was the most useful way to obtain antisera demonstrating individually specific antigenic determinants on the subunit by direct precipitation. Still other determinants were apparently destroyed by mild reduction of the γM molecule. Reduction and reassociation of mixtures of two monoclonal γM-globulins resulted in formation of hybrid molecules containing subunits of different origin. Individually specific antisera against the two components were useful for demonstrating hybrid formation. Serological activity, i.e., cold agglutinin activity, was present in the hybrid molecules.
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