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

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.

Alpha C protein-specific immunity in humans with group B streptococcal colonization and invasive disease

“…Two previous reports have addressed α C-specific antibody in humans. Bevanger [12] found high antibody activity against α C protein in one patient with septicaemia caused by an α C protein producing strain. Larsson et al [13] compared antibody concentrations in sera from 13 mothers of neonates infected with α C-expressing GBS concentration in sera from mothers of non-infected neonates and found no association between α C-specific antibody concentration and risk for invasive infection.…”

“…Thus, α C protein is an attractive candidate GBS vaccine component. Although naturally occurring α C protein-specific antibodies have been found in human sera [12,13], no work published to date has addressed the antibody response after exposure to α Ccontaining GBS strains through colonization or invasive disease or its role in immunity against GBS infection in humans.…”

Characterisation of invasive group B streptococci based on investigation of surface proteins and genes encoding surface proteins

“…The first surface protein identified in GBS was the C antigen [14]. The C antigen is composed of the α and β proteins [15]. A GBS strain can express α‐C‐protein or β‐C‐protein, or both.…”

Mouse‐Protective Antibodies Against The Ibc Proteins of Group B Streptococci

“…Antisera which contained antibodies against the a or p antigen of group B streptococci protected mice from lethal infection by serotype Ia bacteria which produced the corresponding antigen. Protective effect was not observed in animals injected with a strain which did not produce the a or (3 antigen, or which produced the heterologous antigen. These results confirm observations by Lance-Jeld (12) that antiserum against the Ibc protein fraction protected mice challenged by Ibc-containing strains.…”

“…They all contained the type Ia polysaccharide. Strain A909 also produced both of the a and p antigens, strain 335 the a antigen, and strain 70339 the p antigen of the Ibc proteins (3,7). The strain 090 did not produce Ibc proteins.…”