The influence of normal guinea-pig serum and tissue culture assay system on foot-and-mouth disease virus neutralisation.

The inclusion of normal guinea-pig serum in neutralisation reactions involving foot-and-mouth disease virus (FMDV) increased the neutralisation titre and rate of neutralisation by guinea-pig antiserum derived from animals convalescent from FMDV. Such inclusion had little or no effect on neutralisation involving guinea-pig antiserum collected early in infection or early or convalescent bovine antisera. Higher neutralisation titres and more rapid neutralisation were found from assay in bovine thyroid cells than in IB-RS-2 cells. Not all the increase in neutralising activity was removed by heating at 56 degrees C, indicating that other factors in addition to complement were responsible. In some tests a virus fraction resisting neutralisation was found and, when rabbit anti-guinea-pig gamma-globulin was added, an increase in neutralisation resulted, suggesting that most of the persistent virus fraction was due to the presence of infective virus-antibody complexes.