A new complement-dependent bactericidal factor found in nonimmune mouse sera: specific binding to polysaccharide of...

It has been shown that nonimmune mouse sera contain a complement-dependent bactericidal factor that reacts specifically with Ra chemotype Salmonella. In this study we investigate a specific determinant to which this factor binds. This factor bound to Ra chemotype lipopolysaccharide (LPS) but not to S or Re chemotype LPS. The binding was markedly inhibited by N-acetyl-D-glucosamine (GlcNAc), which was the nonreducing terminal of the Ra polysaccharide chain and by certain monosaccharides structurally relating to L-glycero-D-mannoheptose, a terminal component of a side branch of Ra polysaccharide. The factor bound to the Ra bacteria could be eluted with a medium containing GlcNAc. These results indicate that the specific determinant is the polysaccharide region of LPS characteristic of Ra chemotype Salmonella. Ca2+ but not Mg2+ was required for the specific binding of the factor to cells of Ra bacteria. A molecule composed of a polypeptide of 28,000 m.w. was found in the active fraction obtained by the monosaccharide elution. However, no polypeptides corresponding to light and heavy chains of mouse immunoglobins were detected from the active fraction.