Characterization of Influenza Antibodies by Serum

In preceding reports (1, 2) antibody responses to monovalent influenza virus vaccines were characterized for three age groups including children (age 4 to 10), recruits (age 17 to 25) and adults (older than 30). The peculiar patterns noted with sera from each age group indicated that influenza antigens experienced early in life produced a continuing specific effect on antibody formation (3-9). This interpretation has been subjected to test by absorbing sera with virus and measuring the remaining hemagglutination-inhibiting levels with other strains. Using previously described serum absorption technics with virus-coated erythrocytes (10), it has been possible to analyze the sera demonstrating that hemagglutination-inhihiting titers obtained for strains are composites of different antibodies. The data also demonstrated that antibody in some human sera might be highly cross-reactive and inhibitory for distantly related strains, such as Swine-1931 and FM1-1947. It is now clear that the range of reactivity can be defined by removing that antibody which is reactive with a given strain. In this manner information was obtained concerning the nature of antibody in serum from persons who have had experience with many or few antigenic variants of influenza virus. Immunologic relationships among strains became clearly evident from these results. I t was observed that absorption with one Type A strain often removed antibody against all Type A and A-prime strains. The phenomenon has been even more strikingly demonstrated using sera from ferrets that had been successively infected with several antigenically different but related strains of virus. In sera from either experimental animals or man a persistent antibody orientation to the strain of first antigenic experience is demonstrated.