Kay Johswich

Ligand specificity of the anaphylatoxin C5L2 receptor and its regulation on myeloid and epithelial cell lines

During complement activation the pro-inflammatory anaphylatoxins C3a and C5a are generated, which interact with the C3a receptor and C5a receptor (CD88), respectively. C5a and its degradation product C5a-des-Arg74 also bind to the C5a receptor-like 2 (C5L2). C3a and C3a-des-Arg77, also called acylation-stimulating protein, augment triglyceride synthesis and glucose uptake in adipocytes and skin fibroblasts. Based on data obtained using transfected HEK293 and RBL cells, C5L2 is additionally proposed as a functional receptor for C3a and C3a-des-Arg77. Here we use 125I-ligand binding assays and flow cytometry with fluorescently labeled ligands to demonstrate that neither C3a nor C3a-des-Arg77 binds to C5L2. C5L2 expression and its regulation are investigated on various cell lines by a novel C5L2-restricted binding assay and quantitative real time PCR. Dibutyryl cAMP and interferon-γ induce up-regulation of this receptor on myeloblastic cell lines (U937 and HL-60), whereas tumor necrosis factor-α (TNF-α) has no effect. In contrast, epithelial HeLa cells are found to constitutively express C5L2 but not the C5a receptor. In HeLa cells, interferon-γ and TNF-α drastically reduce C5L2 expression. No C5a-dependent Ca2+ signaling is observed even in these cells endogenously expressing C5L2. Taken together, C5L2 is not a receptor for C3a or C3a-des-Arg77. Thus, this receptor is unlikely to be directly involved in lipid metabolism. Instead, the identification of stimuli modifying C5L2 expression indicates that C5L2 is a highly regulated scavenger receptor for C5a and C5a-des-Arg74.

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

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.

Invasive Potential of Nonencapsulated Disease Isolates of Neisseria meningitidis

ABSTRACT The capsule of Neisseria meningitidis is the major virulence factor that enables this bacterium to overcome host immunity elicited by complement and phagocytes, rendering it capable of surviving in blood. As such, nonencapsulated N. meningitidis isolates are generally considered nonpathogenic. Here, we consider the inherent virulence of two nonencapsulated N. meningitidis isolates obtained from our national surveillance of infected blood cultures in Canada. Capsule deficiency of both strains was confirmed by serology and PCR for the ctrA to ctrD genes and siaA to siaC genes, as well as siaD genes specific to serogroups B, C, Y, and W135. In both strains, the capsule synthesis genes were replaced by the capsule null locus, cnl-2. In accordance with a lack of capsule, both strains were fully susceptible to killing by both human and baby rabbit complement. However, in the presence of cytidine-5′ monophospho-N-acetylneuraminic acid (CMP-NANA), allowing for lipooligosaccharide (LOS) sialylation, a significant increase of resistance to complement killing was observed. Mass spectrometry of purified LOS did not reveal any uncommon modifications that would explain their invasive phenotype. Finally, in a mouse intraperitoneal challenge model, these nonencapsulated isolates displayed enhanced virulence relative to an isogenic mutant of serogroup B strain MC58 lacking capsule (MC58ΔsiaD). Virulence of all nonencapsulated isolates tested was below that of encapsulated serogroup B strains MC58 and B16B6. However, whereas no mortality was observed with MC58ΔsiaD, 5/10 mice succumbed to infection with strain 2275 and 2/11 mice succumbed to strain 2274. Our results suggest the acquisition of a new virulence phenotype by these nonencapsulated strains.

The Transcription Factors AP-1 and Ets Are Regulators of C3a Receptor Expression

The anaphylatoxin C3a is a proinflammatory mediator generated during complement activation. The tight control of C3a receptor (C3aR) expression is crucial for the regulation of anaphylatoxin-mediated effects. Key factors regulating constitutive expression of the C3aR in the mast cell line HMC-1 and receptor induction by dibutyryl-cAMP in monomyeloblastic U937 cells were determined by functional characterization of the C3aR promoter. Nucleotides -18 to -285 upstream of the translational start site proved to be critical for promoter activity in HMC-1 cells. Binding sites for the transcription factors AP-1 and Ets could be located. Overexpressed c-Jun/c-Fos (AP-1) and Ets-1 led synergistically to increased promoter activity that was substantially reduced by site-directed mutagenesis of the corresponding elements within the C3aR promoter. In HMC-1 cells, Ets interacted directly with the predicted binding motif of the C3aR promoter as determined by electromobility shift assays. AP-1 binding to the C3aR promoter was augmented during C3aR induction in U937 cells. A retroviral gene transfer system was used to express a dominant negative mutant of Ets-1 in these cells. The resulting cells failed to up-regulate the C3aR after stimulation with dibutyryl-cAMP and showed decreased AP-1 binding, suggesting that Ets acts here indirectly. Thus, it was established that Ets and the AP-1 element mediates dibutyryl-cAMP induction of C3aR promoter activity, hence providing a mechanistic explanation of dibutyryl-cAMP-dependent up-regulation of C3aR expression. In conclusion, this study demonstrates an important role of AP-1 and a member of the Ets family in the transcriptional regulation of C3aR expression, a prerequisite for the ability of C3a to participate in immunomodulation and inflammation.

A native outer membrane vesicle vaccine confers protection against meningococcal colonization in human CEACAM1 transgenic mice

BACKGROUND The effect of protein-based meningococcal vaccines on prevention of nasopharyngeal colonization has been difficult to investigate experimentally because a reliable animal colonization model did not exist. METHODS Human CEACAM1 transgenic mice, which can be colonized by meningococci, were immunized IP with one of two meningococcal native outer membrane vesicle (NOMV) vaccines prepared from mutants with attenuated endotoxin (lpxL1 knockout) and over-expressed sub-family B Factor H-binding proteins (FHbp). Animals were challenged intranasally two weeks after the third dose with wild-type strain H44/76, or were treated IP with anti-NOMV serum before and during the bacterial challenge. RESULTS The NOMV-1 vaccine, prepared from the serogroup B H44/76 mutant, elicited ∼40-fold higher serum bactericidal antibody titers against the wild-type H44/76 challenge strain than the NOMV-2 vaccine prepared from a heterologous serogroup W mutant strain with different PorA and FHbp amino acid sequence variants. Compared to aluminum hydroxide-immunized control mice, the efficacy for prevention of any H44/76 colonization was 93% (95% confidence interval, 52-99, P<0.0001) for the NOMV-1 vaccine, and 19% (-3-36, P=0.23) for NOMV-2. NOMV-2-vaccinated mice had a 5.6-fold decrease in geometric mean CFU of bacteria per animal in tracheal washes compared to control mice (P=0.007). The efficacy of passive administration of serum from NOMV-1-vaccinated mice to immunologically naïve mice against colonization was 44% (17-61; P=0.002). CONCLUSIONS Both NOMV vaccines protected against meningococcal colonization but there was greater protection by the NOMV-1 vaccine with antigens matched with the challenge strain. Meningococcal vaccines that target protein antigens have potential to decrease colonization.

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

ABSTRACT Neisseria meningitidis asymptomatically colonizes the human upper respiratory tract but is also the cause of meningitis and severe septicemia. Carriage or disease evokes an immune response against the infecting strain. Hitherto, we have known little about the breadth of immunity induced by natural carriage of a single strain or its implications for subsequent infectious challenge. In this study, we establish that transgenic mice expressing human CEACAM1 support nasal colonization by a variety of strains of different capsular types. Next, we nasally challenged these mice with either of the N. meningitidis strains H44/76 (serogroup B, ST-32) and 90/18311 (serogroup C, ST-11), while following the induction of strain-specific immunoglobulin. When these antisera were tested for reactivity with a diverse panel of N. meningitidis strains, very low levels of antibody were detected against all meningococcal strains, yet a mutually exclusive “fingerprint” of high-level cross-reactivity toward certain strains became apparent. To test the efficacy of these responses for protection against subsequent challenge, CEACAM1-humanized mice exposed to strain 90/18311 were then rechallenged with different N. meningitidis strains. As expected, the mice were immune to challenge with the same strain and with a closely related ST-11 strain, 38VI, while H44/76 (ST-32) could still colonize these animals. Notably, however, despite the paucity of detectable humoral response against strain 196/87 (ST-32), this strain was unable to colonize the 90/18311-exposed mice. Combined, our data suggest that current approaches may underestimate the actual breadth of mucosal protection gained through natural exposure to N. meningitidis strains.