Neisseria Heparin Binding Antigen is targeted by the human alternative pathway C3-convertase.

Martina Di Fede,Silvia Rossi Paccani,Isabel Delany,Massimiliano Biagini,Alfredo Pezzicoli,Sara Marchi,Manuele Martinelli,Elena Cartocci,Alessandra Greco,Carlo Parillo,Daniela Flavia Hozbor

doi:10.1371/journal.pone.0194662

Abstract

Neisserial Heparin Binding Antigen (NHBA) is a surface-exposed lipoprotein specific for Neisseria and constitutes one of the three main protein antigens of the Bexsero vaccine. Meningococcal and human proteases, cleave NHBA protein upstream or downstream of a conserved Arg-rich region, respectively. The cleavage results in the release of the C-terminal portion of the protein. The C-terminal fragment originating from the processing of meningococcal proteases, referred to as C2 fragment, exerts a toxic effect on endothelial cells altering the endothelial permeability. In this work, we reported that recombinant C2 fragment has no influence on the integrity of human airway epithelial cell monolayers, consistent with previous findings showing that Neisseria meningitidis traverses the epithelial barrier without disrupting the junctional structures. We showed that epithelial cells constantly secrete proteases responsible for a rapid processing of C2 fragment, generating a new fragment that does not contain the Arg-rich region, a putative docking domain reported to be essential for C2-mediated toxic effect. Moreover, we found that the C3-convertase of the alternative complement pathway is one of the proteases responsible for this processing. Overall, our data provide new insights on the cleavage of NHBA protein during meningococcal infection. NHBA cleavage may occur at different stages of the infection, and it likely has a different role depending on the environment the bacterium is interacting with.

Highlights

Neisseria meningitidis, a gram-negative obligate human commensal typically residing in nasopharyngeal mucosa, is a pathogenic member of the Neisseria family and a leading cause of fatal sepsis and bacterial meningitis worldwide
The recent finding that Neisserial Heparin Binding Antigen (NHBA) protein is more expressed and cleaved at lower temperatures than 37 ̊C [12], which are temperatures encountered during N. meningitidis initial colonization of the upper respiratory tract, led us to hypothesize that C2 fragment could alter the epithelial permeability and facilitate the traversal of N. meningitidis through the epithelium
When we checked the stability of the C2 fragment during permeability assays by performing a Western blot analysis on treated cell supernatants, a second shorter band was observed (Fig 1A), indicating that epithelial cells were able to process the protein during the assays

Summary

Introduction

A gram-negative obligate human commensal typically residing in nasopharyngeal mucosa, is a pathogenic member of the Neisseria family and a leading cause of fatal sepsis and bacterial meningitis worldwide. Based on the immunologic reactivity of the capsular polysaccharides, 12 distinct serogroups have been defined (A, B, C, E, H, I, K, L, W, X, Y and Z), six of which cause life-threatening disease (A, B, C, W, X and Y) [1]. In non-epidemic settings, approximately 10% of healthy individuals at any time carry N. meningitidis in the upper airways [2]. Acquisition of the bacteria from a healthy carrier or an infected person occurs through close direct contact with respiratory droplets or secretions.

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