Antibody response of pigs to foot-and-mouth disease oil emulsion vaccine: the antibody classes involved.

Groups of three pigs were vaccinated with water-in-oil emulsion vaccine and revaccinated either 21 and 148 or 106 days later. Sera were taken periodically for six months and fractionated into heavy and light elements on sucrose density gradients. The heavier fraction contained IgM and the lighter fraction IgG and IgA. Neutralising antibodies were first detectable eight days after initial vaccination (dpiv), rose to a peak between 14 and 21 dpiv and persisted at relatively high titres until the time of revaccination. Neutralising antibody at eight dpiv was attributed to IgM but by 10 to 14 dpiv both IgM and IgG were involved. Thirty-five days (and later) after a single vaccination all the neutralising activity in the sera was due to IgG. The revaccinations produced an increment in the whole serum neutralising titres and in each case both IgM and IgG class antibodies were involved.