Recognition of different epitopes on the Ca & R4 proteins of group B streptococci by normal human & antibodies induced in animals.

BACKGROUND & OBJECTIVES Levels of protective antibodies against Calpha and R4 proteins of the group B streptococci (GBS) have been measured in humans. The findings indicated that the human anti Calpha and anti-R4 antibodies may recognize targets which are different from those recognized by antibodies raised in animals. In the present study normal human serum antibodies which target the GBS proteins Calpha and R4 and immune anti-Calpha and anti -R4 antibodies raised in animals were compared. METHODS The antigens were prepared by extraction of whole cells of GBS with trypsin and purified, and the testing was done by ELISA and Western blotting. RESULTS The immune antibodies showed specificity for the corresponding protein and targeted proteins which had been denatured by hot sodium dodecyl sulphate (SDS) or by heating in a nearly neutral buffer. The human antibodies targeted a site(s) common to Calpha and R4 and failed to bind to the denatured proteins. The bulk of antibodies in sera from healthy pregnant women was directed against the SDS and heat labile determinant(s). INTERPRETATION & CONCLUSION The present results indicated that the immune antibodies were directed against sequential epitopes and the normal human serum antibodies against epitopes determined by molecular conformation.