EFFECT OF SIALYLATION OF LIPOPOLYSACCHARIDE OF NEISSERIA-GONORRHOEAE ON RECOGNITION AND COMPLEMENT-MEDIATED KILLING BY MONOCLONAL-ANTIBODIES DIRECTED AGAINST DIFFERENT OUTER-MEMBRANE ANTIGENS

Growth of gonococci in the presence of CMP-N-acetylneuraminic acid (CM P-NANA) has previously been shown to induce resistance to the bacteric idal effect of normal human serum and is accompanied by sialylation of the gonococcal lipopolysaccharide (LPS). We have used monoclonal anti bodies (mAbs) to compare the effect of LPS sialylation on recognition of gonococci and complement-mediated killing by antibodies directed ei ther against LPS or against defined epitopes on outer-membrane protein PI, Despite differences in binding to sialylated LPS on Western blots , all three mAbs directed against LPS showed considerably reduced bind ing to gonococci grown in the presence of CMP-NANA and a concomitant r eduction in ability to promote complement-mediated killing, In contras t, mAbs directed against previously defined epitopes on a surface expo sed loop of PI showed little difference in binding between sialylated and non-sialylated gonococci and promoted killing of the sialylated go nococci, Similarly a mAb directed against an epitope on a loop of the outer-membrane Rmp protein, which had previously been shown to block k illing by antibodies directed against other surface antigens, also exe rted a blocking effect with sialylated gonococci, Thus in the present study the continued biological effect of mAbs was correlated with the ability of the antibody to recognize surface-exposed epitopes on sialy lated gonococci, Despite the presence of the sialylation which is like ly to occur in vivo, it should be possible to induce complement-mediat ed killing by focusing the immune response to those surface-exposed ep itopes which are least susceptible to the potential inhibitory effect of LPS sialylation.