Enzyme immunoassay of antibodies to Sjögren's syndrome B antigen.

I describe a solid-phase enzyme immunoassay of IgG-IgA-, and IgM-type antibodies to Sjögren's syndrome B antigen. Polystyrene tubes are coated with the purified antigen. The antibodies are allowed to bind with their antigens, and then detected with alkaline-phosphatase-conjugated anti-human IgG, IgA, or IgM sera. The amount of alkaline phosphatase fixed to the tubes is determined in pH 10.0 diethanolamine buffer at 37 degrees C with p-nitrophenyl phosphate as substrate. The absorbance of the p-nitrophenolate ion liberated in 1 h at 37 degrees C is measured at 406 nm. When rheumatoid factor is present, the values obtained for IgG antibodies are too low, and those for IgM antibodies are too high.