5 - Monoclonal Antibodies to the Lipopolysaccharide and Capsular Polysaccharide of Bacteroides fragilis

Abstract

This chapter presents the results of a study on monoclonal antibodies (MAbs) to two pathogenetically interesting surface structures of B. fragilis, lipopolysaccharide (LPS), and capsular polysaccharide (CPS). MAbs have been produced against B. fragilis LPS and CPS by immunizing mice before hybridization with air-exposed whole organisms or Triton X-100-treated outer membranes (OM) of B. fragilis. The LPS MAbs appeared to react with a determinant located in the oligosaccharide part of LPS and containing D-galactose. This determinant is common to most B. fragilis isolates. A determinant closely resembling it also occurred in some B. thetaiotaomicron and B. ovatus strains, but not in other anaerobic and aerobic bacteria tested. Electron microscopy-immunocytochemistry (EIC) studies showed that the determinant is located on the surface of OM, but it is expressed only on about 10% of bacterial cells taken from the same culture. This suggests that the occurrence of this determinant depends on the growth phase of the organism. The target determinant of the CPS MAbs appeared to be very labile. It can usually be demonstrated only in fresh B. fragilis isolates. It has been shown by EIC that the determinant is located in the outer part of the B. fragilis capsule.