[The role of the different immunoglobulins in the milk ring test used for the detection of brucellosis (author's transl)].

The serum immunoglobulins obtained from one heifer vaccinated against brucellosis, and milk immunoglobulins from a cow suffering from a natural udder infection, were purified. The preparations were more than 99.5 per cent pure. The role of each immunoglobulin in the milk ring test was determined. Fractions sIgA and IgM induce the formation of a broad coloured ring after 1 hour's incubation at 37 degrees C. Under these same conditions, no ring was observed with IgG1 or IgG2 but the coloured agglutinated bacteria were visible at the bottom of the tube. The maintenance of the tubes at 4 degrees for 18 hours increased the sensitivity of the milk ring test, with all immunoglobulins. When the four immunoglobulins were simultaneously present in milk, the formation of the coloured ring prevented the formation of a deposit of agglutinated bacteria on the bottom of the tube. In this case, agglutination at the bottom of the tube occured only at dilutions above that giving the coloured ring. Addition of IgG1 and IgG2 to the mild containing sIgA or IgM slightly increased the title of the milk ring test: one part of the deposit of agglutinated bacteria rose to the surface with the fat globules.