On the capacity of pepsin-digested antibody to neutralize adenovirus infectivity.

Rabbit hyperimmune γ-globulin was produced against type 5 adenovirus. This was digested with pepsin to produce bivalent fragments of antibody. These fragments retained the capacity to precipitate with antigen, but were defective in their power to neutralize virus infectivity. Their neutralizing capacity deviated from that of native antibody in the following ways: 1. The proportion of virus neutralized was smaller. 2. The progressive neutralization of virus ceased within 10–15 minutes of mixing virus and fragments of antibody. 3. The rate of neutralization of virus depended only on the concentration of fragments of antibody, and was independent of the relative proportions of virus and antibody fragments. 4. Over the ranges tested the antibody fragments inactivated an approximately constant proportion of virus irrespective of the amount of virus used in the primary mixture. There is a brief discussion of the significance of these results for an understanding of the mechanism by which complete antibody neutralizes virus infectivity.