Isolation of a protein antigen from Coxiella burnetii.

Antigens prepared from Coxiella burnetti, strain Frankfurt, phase II, propagated in persistently infected Buffalo Green Monkey (BGM) cell cultures were purified by guanidinium hydrochloride treatment and chloroform/methanol extraction. By ELISA analysis, chloroform/methanol residues (CMR) proved to be free of host cell antigens. The CMR were sensitive to trypsin, pronase E and proteinase K, as determined by absorption-kinetics of CMR suspensions at 600 nm and release of protein. Coomassie blue stained SDS polyacrylamide gels of proteinase hydrolysates from CMR revealed only a single component of apparently 27,000 D. Silver stained gels, however, showed a second component of apparently 12,000 D. In contrast, from untreated native C. burnetii a large variety of proteins, most of them protease-sensitive, were released by detergents at low temperatures, but the 27,000 D component was only solubilized at 60-100 degrees C. The 27,000 D component was obviously the major protein of CMR as well as of whole cells. Antigenicity of this 27,000 D protein could be demonstrated by agargel precipitation test, ELISA and immunoperoxidase techniques applying antisera raised against whole cells and against the extracted component. The component was also recognized in a dot immunobinding assay by sera from guinea pigs infected with cloned C. burnetii stain Nine Mile, phase I, thus indicating an important role of this antigen in C. burnetii specific immune response.