Global Analysis of Neutrophil Responses to Neisseria gonorrhoeae Reveals a Self-Propagating Inflammatory Program

Abstract

An overwhelming neutrophil-driven response causes both acute symptoms and the lasting sequelae that result from infection with Neisseria gonorrhoeae. Neutrophils undergo an aggressive opsonin-independent response to N. gonorrhoeae, driven by the innate decoy receptor CEACAM3. CEACAM3 is exclusively expressed by human neutrophils, and drives a potent binding, phagocytic engulfment and oxidative killing of Opa-expressing bacteria. In this study, we sought to explore the contribution of neutrophils to the pathogenic inflammatory process that typifies gonorrhea. Genome-wide microarray and biochemical profiling of gonococcal-infected neutrophils revealed that CEACAM3 engagement triggers a Syk-, PKCδ- and Tak1-dependent signaling cascade that results in the activation of an NF-κB-dependent transcriptional response, with consequent production of pro-inflammatory cytokines. Using an in vivo model of N. gonorrhoeae infection, we show that human CEACAM-expressing neutrophils have heightened migration toward the site of the infection where they may be further activated upon Opa-dependent binding. Together, this study establishes that the role of CEACAM3 is not restricted to the direct opsonin-independent killing by neutrophils, since it also drives the vigorous inflammatory response that typifies gonorrhea. By carrying the potential to mobilize increasing numbers of neutrophils, CEACAM3 thereby represents the tipping point between protective and pathogenic outcomes of N. gonorrhoeae infection.

Selection for a CEACAM Receptor-Specific Binding Phenotype during Neisseria gonorrhoeae Infection of the Human Genital Tract

“…We recently revealed that CEACAM3 engagement activates a proinflammatory transcriptional program in neutrophils, which results in production of proinflammatory cytokines via a signaling pathway that is independent of bacterial phagocytosis (47). Consistent with this, infection with the Opa ϩ phase variant led to significantly higher levels of both TNF and IL-8 (Fig.…”

“…We hypothesized that the high prevalence of Opa expression in our LPCIs suggests that Opa proteins facilitate infection. However, since each Opa variant may have a different spectrum of CEACAM binding, since the spectrum of binding has the potential to drastically affect the host cellular response to infection (28,30,32,38,43,44,47), and since the pattern of CEACAM expression varies between sexes and cell types, we sought to characterize the binding specificity of each N. gonorrhoeae isolate.…”

“…Characterization of individual CEACAM function in neutrophilic cell lines showed that Opa-mediated neutrophil activation is mediated by CEACAM3 signaling, while CEACAM1 and CEACAM6 allowed bacterial internalization without triggering production of reactive oxygen species (ROS) or release of toxic granule proteins (44). However, all of the studies focusing on neutrophil responses to Opa-CEACAM binding have been done exclusively with the commonly studied N. gonorrhoeae strains MS11 (44,45,47,61,62) and FA1090 (63,64).…”

“…However, expression of human CEACAM1 in a mouse allowed persistent colonization by N. meningitidis (37), and a mouse model expressing human CEACAM5 showed increased gonococcal recovery from the lower genital tract (38). In contrast, Opa binding to neutrophil CEACAM3 drives inflammation and gonococcal clearance (39)(40)(41)(42)(43)(44)(45)(46)(47). The specific contribution of Opa binding to individual CEACAMs for N. gonorrhoeae colonization and pathogenesis in humans and how differences in CEACAM distribution between the sexes might affect the outcome of infection have not been addressed.…”

Neisserial Opa Protein–CEACAM Interactions: Competition for Receptors as a Means of Bacterial Invasion and Pathogenesis

“…22–24 CEACAM3 contains an immunoreceptor tyrosine-based activation motif (ITAM), which recruits kinases (Src family kinases, such as Syk) upon activation to propagate pro-inflammatory signaling cascades. 25–28 CEACAM3, which is expressed exclusively on human neutrophils and other granulocytes, is thought to have evolved as innate immune protection, as it has no known endogenous ligand, but interacts specifically with proteins expressed on the surface of human-specific bacterial pathogens such as Neisseria . 1 These CEACAM3 interactions mediate uptake of the pathogen, which induces the oxidative burst as well as toxic granule release to effect pathogen killing.…”