CGM1a antigen of neutrophils, a receptor of gonococcal opacity proteins

Abstract

Neisseria gonorrhoeae (GC) or Escherichia coli expressing phase-variable opacity (Opa) protein (Opa⁺ GC or Opa⁺ E. coli) adhere to human neutrophils and stimulate phagocytosis, whereas their counterparts not expressing Opa protein (Opa⁻ GC or Opa⁻ E. coli) do not. Opa⁺ GC or E. coli do not adhere to human lymphocytes and promyelocytic cell lines such as HL-60 cells. The adherence of Opa⁺ GC to the neutrophils can be enhanced dramatically if the neutrophils are preactivated. These data suggest that the components binding the Opa⁺ bacteria might exist in the granules. CGM1a antigen, a transmembrane protein of the carcinoembryonic antigen family, is exclusively expressed in the granulocytic lineage. The predicted molecular weight of CGM1a is ≈30 kDa. We observed specific binding of OpaI⁺ E. coli to a 30-kDa band of polymorphonuclear leukocytes lysates. To prove the hypothesis that the 30-kDa CGM1a antigen from neutrophils was the receptor of Opa⁺ bacteria, we showed that a HeLa cell line expressing human CGM1a antigen (HeLa-CGM1a) bound Opa⁺ E. coli and subsequently engulfed the bacteria. Monoclonal antibodies (COL-1) against CGM1 blocked the interaction between Opa⁺ E. coli and HeLa-CGM1a. These results demonstrate that HeLa cells when expressing the CGM1a antigens bind and internalize OpaI⁺ bacteria.