Murine monoclonal antibodies to type Ib polysaccharide of group B streptococci bind to human milk oligosaccharides.

The chemical structures of the repeating units of the type Ib polysaccharide of group B streptococci and of the desialylated form of this antigen are almost identical to those of some oligosaccharides in human milk and certain fetal antigens. The structural similarities suggested that the molecules may be immunologically cross-reactive. Mouse monoclonal antibodies to the sialylated and nonsialylated forms of the type Ib polysaccharide were produced and tested for their ability to bind to immobilized human milk oligosaccharides. One antibody, SMB19, reacted specifically with the sialylated form of the type Ib polysaccharide and was also bound by an affinity column containing immobilized sialyllacto-N-tetraose a. The antibody was eluted from the affinity column with EDTA, since its binding to the antigen was calcium dependent. A second monoclonal antibody. SIbD2, bound specifically to the nonsialylated form of the type Ib polysaccharide and also to immobilized lacto-N-tetraose. The antibody was eluted from the affinity column at an acidic pH and retained immunologic activity. These results further extend our previous observations that certain antibodies raised against group B streptococci can also react with normal human glycoconjugates.