The identification of an 18,000-molecular-weight antigen specific to big liver and spleen disease.

SUMMARY. Big liver and spleen (BLS) disease is an infectious syndrome of broiler breeders that has been serologically diagnosed worldwide with the agar gel immunodiffusion test. Liver homogenate from an affected broiler breeder was used as the antigen source in this study. This paper reports the identification, from liver, of a soluble basic protein antigen (molecular weight 18,000) that is specific to BLS disease. The antigen was partially purified from soluble extract of liver using a two-step fractionation procedure comprising Sephacryl S200 gel filtration and carboxymethyl (CM) cellulose cation exchange. After cation exchange, the partially purified (CM) antigen contained approximately 12 proteins. Immunoblotting was used to identify the single BLS disease-specific antigen. In addition, a polyclonal rabbit antiserum raised to the CM antigen was found to be monospecific to the 18,000-molecular-weight antigen by immunoblotting on the CM antigen. This serum was also of use in specifically detecting intracellular BLS disease antigen in frozen cryostat sections by indirect immunofluorescence.