Dose-response relationships in a microneutralization test for foot-and-mouth disease viruses

Two-dimensional quantal microneutralization tests on foot-and-mouth disease viruses, in which neutralizing antibody activity was titrated against a serial range of virus doses, demonstrated a variety of dose-response curves some of which were rectilinear, others clearly curvilinear. Moreover, in the case of the non-linear responses obtained with some antisera, the shape of the curve was such that antibody titres recorded with doses of virus ranging from 103–105 TCD 50 were closely similar. Studies were carried out on the effect of varying the conditions of the test on the shape of the dose-response curve: significant differences were obtained after treatment of the antiserum–virus mixtures with anti-species globulin, and when the test was assayed in cells of differing susceptibility to infection.