In Vivo Adaptation and Persistence of Neisseria meningitidis within the Nasopharyngeal Mucosa

Abstract

Neisseria meningitidis (Nme) asymptomatically colonizes the human nasopharynx, yet can initiate rapidly-progressing sepsis and meningitis in rare instances. Understanding the meningococcal lifestyle within the nasopharyngeal mucosa, a phase of infection that is prerequisite for disease, has been hampered by the lack of animal models. Herein, we compare mice expressing the four different human carcinoembryonic antigen-related cell adhesion molecules (CEACAMs) that can bind the neisserial Opa protein adhesins, and find that expression of human CEACAM1 is necessary and sufficient to establish intranasal colonization. During infection, in vivo selection for phase variants expressing CEACAM1-specific Opa proteins occurs, allowing mucosal attachment and entry into the subepithelial space. Consistent with an essential role for Opa proteins in this process, Opa-deficient meningococci were unable to colonize the CEACAM1-humanized mice. While simple Opa-mediated attachment triggered an innate response regardless of meningococcal viability within the inoculum, persistence of viable Opa-expressing bacteria within the CEACAM1-humanized mice was required for a protective memory response to be achieved. Parenteral immunization with a capsule-based conjugate vaccine led to the accumulation of protective levels of Nme-specific IgG within the nasal mucus, yet the sterilizing immunity afforded by natural colonization was instead conferred by Nme-specific IgA without detectable IgG. Considered together, this study establishes that the availability of CEACAM1 helps define the exquisite host specificity of this human-restricted pathogen, displays a striking example of in vivo selection for the expression of desirable Opa variants, and provides a novel model in which to consider meningococcal infection and immunity within the nasopharyngeal mucosa.

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

“…This ongoing diversification of phenotypes is balanced by ongoing phenotypic selection of variants expressing adhesins or other factors that facilitate infection within an individual and/or within a particular tissue-specific niche. In vitro cell culture and primary cell-based systems have clearly established that most Opa variants can bind one or more human CEACAMs, and transgenic mouse-based studies corroborate the importance of this binding for the establishment of infection (37,38). Experimental human urethral model studies also suggest the importance of Opa proteins and pilus (6,(12)(13)(14)(65)(66)(67), yet the binding specificity of Opa variants expressed during human infection had not been addressed before this study.…”

“…Due to the host specificity of Neisseria, mouse models remain limited. 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).…”

Sterilizing Immunity Elicited by Neisseria meningitidis Carriage Shows Broader Protection than Predicted by Serum Antibody Cross-Reactivity in CEACAM1 -Humanized Mice

“…Generation of CEACAM1-humanized mice was described in detail in the work of Gu et al (18). The infection procedure was carried out as previously described (17). Inocula were obtained by resuspending the lawn of growth from an overnight agar plate into 1 ml of phosphate-buffered saline (PBS) containing 1 mM MgCl 2 (PBS/Mg), with adjustment to 10 7 CFU/ml, and 32 mg/ml of human holotransferrin was added (Sigma-Aldrich, Oakville, Canada).…”

“…Previously, we observed carriage of serogroup B meningococci after nasal inoculation of transgenic mice expressing human CEACAM1 but not their wild-type (WT) littermates (17). In order to assess the applicability of this model for other meningococcal isolates, we intranasally infected CEACAM1-humanized mice versus WT littermates with inocula of serogroup A, B, C, and Y strains and then recovered viable bacteria in the nasal tissues at day 3 postinfection.…”

“…This model allows N. meningitidis to intimately associate with the nasal mucosa as its Opa protein adhesins bind to human CEACAM1, allowing us to dissect both innate and adaptive responses to infection (17). In this study, we take advantage of this mouse model to assess strain-specific crossprotection conferred upon N. meningitidis colonization of the respiratory mucosa.…”