Role of environment in the development of "natural" hemagglutinins in Minnesota miniature swine.

"Natural" hemagglutinin titers against a panel of fixed erythrocyte antigens were determined for groups of Minnesota miniature swine reared conventionally, in a specific pathogen-free facility, and in germfree isolators. Sera were assayed for hemagglutination (HA) titers by the microtiter method against 12 species of erythrocytes stabilized by treatment with pyruvic aldehyde and formaldehyde. These erythrocytes were stable for up to 2 years and gave slightly enhanced HA titers as compared to fresh, unfixed erythrocytes. Of the sera from conventional swine tested, the highest "natural" HA titers were directed towards rabbit, cat, swine dog, and burro erythrocytes (greater than 1:1,000), intermediate titers were detected against human A, B, and O, and sheep, pig, and chicken erythrocytes (1:64 to 1:1,000), whereas the lowest titers were found against ox and goat erythrocytes (less than 1:8). Titers obtained with sera from specific pathogen-free swine were 2- to 16-fold lower than those of conventional swine, but were of a similar distribution with regard to the species of erythrocyte tested. Germfree swine sera uniformly exhibited HA titers less than 1:4 against all species of erythrocytes. The majority of these hemagglutinins were immunoglobulin M class but there were some agglutinins of immunoglobulin A class and a slight amount of immunoglobulin G class. Specificity of these agglutinins was examined by absorption tests. The results are consistent with the hypothesis that natural hemagglutinins develop due to dietary or microbial antigenic stimulation, or both.