Contribution of C4b-binding protein to interactions of Neisseria gonorrhoeae with human neutrophils

Neisseria gonorrhoeae (Gc) is the causative agent of the sexually transmitted infection gonorrhea. With an estimated 87 million cases worldwide annually, increasing resistance to last-line antibiotics, and no protective vaccine, Gc is an urgent public health concern. Investigating Gc-host interactions is crucial to identify new drug targets and decrease the global burden of disease. The host response to Gc is highly inflammatory and drives a robust influx of neutrophils to the site of infection. To persist in its obligate human host, Gc has evolved strategies to evade the innate response and survive neutrophil exposure, including sequestration of host proteins for protection. Our lab recently reported that in the absence of all other complement factors, human complement inhibitor C4b-binding protein (C4BP) from serum binds outer membrane protein porin on Gc and reduces killing and phagocytosis by neutrophils. However, the molecular mechanisms underlying the complement- independent role of C4BP in protecting Gc from neutrophil killing remain undefined. The overarching goal of this fellowship proposal is to define the molecular mechanisms driving complement-independent protection of Gc by C4BP during neutrophil interaction. One crucial interaction at the Gc-neutrophil interface is binding of Gc Opacity proteins (Opa) to selected human carcinoembryonic-antigen related adhesion molecules (CEACAM). Opa proteins are Gc surface proteins that act as adhesins and invasins via interaction with CEACAMs, which are a family of immunoglobulin domain-containing receptors present on neutrophils and other cell types. Importantly, C4BP-mediated protection from neutrophils is restricted to Opa-expressing Gc. My preliminary data suggests that C4BP interrupts interactions between Opa and CEACAM3, which is a neutrophil-activating receptor, but not CEACAM1, which is canonically inhibitory. I hypothesize that C4BP enhances Gc survival by blocking stimulatory Opa-CEACAM interactions to modulate neutrophil signaling and prevent antimicrobial activities. To evaluate the molecular mechanisms of C4BP’s complement-independent, protective role against killing by neutrophils, I propose two Specific Aims: 1) Evaluate how CEACAM3 binding and signaling initiation are impeded by C4BP binding to Gc and 2) Define the consequences of C4BP on Gc and neutrophil outcomes over time. I will use a combination of targeted and unbiased approaches to dissect these mechanisms and define the contributions of C4BP to Gc-neutrophil interactions. Completion of this project will reveal the molecular mechanisms responsible for the complement-independent protection of Gc by C4BP, provide valuable insight into the success of Gc within its obligate human host, and uncover potential pathways that could be exploited by emerging C4BP-based therapeutics. The proposed studies will provide me with rigorous training in the study of host-pathogen interactions, which will help me achieve my goal of becoming an independent academic investigator in microbial pathogenesis. Project Number: 1F31AI188753-01A1 | Fiscal Year: 2025 | NIH Institute/Center: National Institute of Allergy and Infectious Diseases (NIAID) | Principal Investigator: Mary Broden | Institution: UNIVERSITY OF VIRGINIA, CHARLOTTESVILLE, VA | Award Amount: $38,922 | Activity Code: F31 | Study Section: Special Emphasis Panel[ZRG1 F07A-W (20)] View on NIH RePORTER: https://reporter.nih.gov/project-details/1F31AI18875301A1