Colostral IgA, IgG, and IgM-IgA fractions as fluorescent antibody for the detection of the coronavirus of transmissible gastroenteritis.

Colostrum from sows and gilts inoculated with virulent transmissible gastroenteritis virus was fractionated into the 3 major immunoglobulin classes, IgA, IgG, and IgM-IgA fractions, by chromatographic and gel-filtration procedures. Each fraction was assayed for purity with rabbit anti-porcine serum and rabbit monospecific anti-porcine IgG, anti-porcine IgA, and anti-porcine IgM. These analyses showed that the IgG and IgA fractions were pure. The IgM fraction contained some IgA in the polymeric form and was designated the IgM-IgA fraction. Each Ig was assayed for virus-neutralizing activity on swine testes cells by the plaque-reduction method before and after conjugation with fluorescein isothiocyanate. On the basis of activity per milligram of protein, the virus-neutralizing titers were 1:641, 1:44, and 1:6.8 for the IgA, IgG, and IgM-IgA fractions respectively; the fluorescent antibody titers were 1:31.3, 1:0.1, and 1:15.6, respectively, for the same Ig.