Summary IgM, electrophoretically fast IgG and slow IgG fractions of rabbit γ-globulin were separated using DEAE-cellulose columns, gel filtration and/or ultracentrifugation. The early appearance of IgM and fast IgG antibodies and the later appearance of slow IgG antibodies were correlated in hemagglutination-inhibition (HI) tests and in plaque reduction neutralization tests (NT). All fractions from 7-day immune serum were potentiated in NT by fresh normal serum, but the effect declined markedly during immunization. IgM and IgG fractions were potentiated by the addition of anti-rabbit γ-globulin to NT mixtures. Dose-response experiments revealed differences in the combining capacities of IgG fractions obtained from the same serum or at different times during immunization. A persistent fraction of approximately 10% was observed in NT with IgM antibodies. In HI tests with other group B arboviruses, IgM and slow IgG antibodies cross-reacted less than fast IgG antibodies. Neutralizing antibodies in the fractions reacted more specifically when tested separately but synergistic activity in cross-reactions was observed when fractions were recombined. Inclusion of fresh serum in cross NT produced some loss of specificity. The results were discussed in relation to the probable disposition of antigen-antibody complexes forming a critical area on each neutralized virus particle.
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E. G. Westaway (1968) studied this question.
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