The Ibc Proteins Of Group b Streptococci: Isolation Of The α and β Antigens by Immunosorbent Chromatography and Test For Human Serum Antibodies Against The Two Antigens

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Abstract
The Ibc protein fraction from group B streptococci contains at least two antigens, named α and β. Rabbit antisera to each of these antigens were used to prepare affinity-purified α and β antigens. Analysis of the purified antigens by SDS-PAGE showed at least three weakly stained proteins in the α antigen -and multiple protein bands in the β antigen preparation. Conditions for optimalization of ELISA for testing of human serum antibodies against these antigens were investigated. When tested at a dilution of 1 in 200, ELISA activity corresponding to an OD405 > 0.2 was shown by 11.2 per cent of 157 blood donor sera in tests with the α antigen, and 77.7 per cent with the β antigen. Increasing antibody activity against the α antigen was shown by a patient with septicaemia caused by an α antigen-producing strain. The antigens were immunoblotted and tested against human and rabbit antibodies. With the α antigen, antibodies from both species produced a diffuse stained area, and with the β antigen multiple stained bands, some of which were colinear with the human and rabbit antibody. Thus, antibodies to the β antigen of group B streptococci are present in a large proportion of the healthy population. These antibodies may be important in the protection against group B streptococcal disease.