Neisseria gonorrhoeae interactions with human polymorphonuclear neutrophils and host proteins were studied in order to understand how the expression of different gonococcal surface components affects bacterial association with host cells and cell surface proteins. Studies were carried out to characterize A) gonococcal interactions with human extracellular matrix proteins and B) the role of fourth oligopeptide loop of gonococcal opacity proteins in mediating neutrophil (PMN) responses to gonococci. A. Attachment of gonococci to extracellular matrix proteins: Gonococcal with or without opacity (Opa) proteins were tested for adherence to plastic coverslips coated with human laminin, vitronectin, fibronectin (FN), collagen type IV or bovine serum albumin (BSA). Neither Opa+ nor Opa- variants showed increased adherence BSA compared to the plastic coverslips alone. Opa+ variants, but not Opa-, adhered significantly more to FN than to BSA. Gonococci expressing Opa A showed 1.8X, 3.8X and 11.2X times greater adherence to laminin, vitronectin and FN, respectively, than to BSA but no increased adherence to collagen type IV. Rabbit anti-human FN antiserum inhibited Opa A attachment to FN by 50% while normal rabbit serum had no effect. Interestingly, PMN responses to Opa+ gonococci were inhibited in a dose-dependent manner by added FN. B. Role of the gonococcal opacity protein fourth loop in mediating human neutrophil responses to gonococci: A peptide representing the conserved surface-exposed Opa protein fourth loop inhibited neutrophil responses to gonococci in suspension and when coated on surfaces directly stimulated neutrophil responses; a control peptide with a scrambled sequence did neither. Rabbit antisera against the fourth loop peptide was opsonic for Opa+ gonococci and affinity-purified anti-fourth loop IgG inhibited PMN non-opsonic responses to gonococci. This suggests a role for the fourth oligopeptide loop in neutrophil interactions.