Further Studies on Effect of Endotoxin on Antibody Response of Rabbit to Common Antigen of Enterobacteriaceae

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Abstract
Summary and Conclusions: Neutralization and precipitation of bacteriophage f2 by γG-immunoglobulin, 5S pepsin fragments and Fab′ fragments were used to test the hypothesis that steric hindrance is important in virus neutralization. There was no demonstrable difference in the capacity of intact γG-immunoglobulin and 5S pepsin fragments to precipitate bacteriophage. The zones of equivalence with γG-immunoglobulin and 5S pepsin fragments were broad. These results suggested that there was no difference in the combining capacities of f2 for bivalent antibodies or for bivalent antibody fragments. As expected, the Fab′ fragments did not precipitate with bacteriophage f2. The antibody to antigen ratios necessary to produce neutralization of bacteriophage correspond to points on the antibody excess end of the equivalence zone of the precipitin curve. In all cases the kinetics of neutralization were first order. The γG-immunoglobulin was most active and the Fab′ fragment was least active. The 5S pepsin fragments were intermediate in activity. However, the neutralization constants were not strictly proportional to molecular weights. This suggests that virus neutralization may not be entirely explicable on the basis of steric hindrance.