The ins and outs of pertussis toxin

Production and characterization of pertussis toxin specific monoclonal and polyclonal antibodies: Implication for toxin purification and detection

BACKGROUND

Pertussis is a pulmonary disease caused by the gram-negative bacteria Bordetella pertussis (BP) with a high fatality rate among newborns and young children. Pertussis toxin (PT) is essential for pertussis pathogenesis as well as production of acellular pertussis vaccines (aPV). Traditional PT purification procedures are laborious and yield low purity and recovery rates. Also, due to the low production levels of PT by BP and the difficulties of purification, an appropriate immunoassay is needed to monitor PT concentrations upstream and downstream of the production process. This study investigates production and application of monoclonal and polyclonal antibodies for efficient PT purification and quantification.

METHODS

Rabbits and mice were immunized with native PT to produce polyclonal and monoclonal antibodies (MAbs). The MAbs were selected based on affinity, isotype and specificity, as determined by enzyme-linked immunosorbent assay (ELISA) and immunoblotting. The native PT antigen was purified using an immunoaffinity column. The purity and recovery rates of native PT were analyzed by ELISA, SDS-PAGE, and immunoblotting. Additionally, monoclonal and polyclonal antibodies were used to establish an ELISA assay for measurement of PT concentration.

RESULTS

A highly pure PT with recovery rates of around 74 ± 4.9 % was obtained following purification by immunoaffinity column, using polyclonal antibodies. Furthermore, the designed ELISA demonstrated suitable reactivity for measurement of the PT antigen.

CONCLUSION

Our results indicate suitability of the produced monoclonal and polyclonal anti-PT antibodies for purification and monitoring of PT by immunoaffinity chromatography and ELISA, respectively. The immunoaffinity method offers an efficient replacement for PT purification in the context of developing aPV.

Hydroxyurea for Malignant Pertussis in Critically Ill Children

OBJECTIVES

Malignant pertussis, the most severe manifestation of Bordetella pertussis infection, is characterized by multiple organ failure and a high mortality rate despite advanced intensive care measures. Hyperleukocytosis is the hallmark of malignant pertussis and necessitates urgent and aggressive interventions. Among the therapeutic options, leukoreduction via whole blood exchange (BE) transfusion has been associated with significant procedural risks and potential clinical deterioration. Hydroxyurea was recently proposed as a pharmacological alternative for leukoreduction. This study reports our clinical experience with hydroxyurea as an alternative to BE in managing infants with malignant pertussis admitted to a PICU.

DESIGN

Prospective case series.

SETTING

A referral PICU in France.

PATIENTS

Critically ill infants (n = 27) with severe pertussis infection.

INTERVENTIONS

Hydroxyurea therapy or BE transfusion.

MEASUREMENTS AND MAIN RESULTS

We reviewed all critically ill infants admitted to our unit for severe pertussis between January 2017 and July 2024. The primary outcome was 28-day survival, and the secondary outcome was the efficacy of hydroxyurea on blood leukocyte count reduction. Among the 27 infants admitted for severe pertussis, 12 exhibited features of malignant pertussis. Of these, seven were treated with hydroxyurea and five with BE. The majority of infants were term and under 3 months old. All patients required ventilatory support, with eight on invasive mechanical ventilation and three receiving extracorporeal membrane oxygenation therapy. Overall mortality was three of 12 (25%). Hydroxyurea was administered at a dose of 20 mg/kg/d for a median duration of 12 days. Hyperleukocytosis was successfully reduced within 7 days.

CONCLUSIONS

Hydroxyurea is an alternative therapy for malignant pertussis infection that can efficiently address hyperleukocytosis with limited mortality.

Heterologous Effects of Pertussis and Influenza Vaccines During Pregnancy on Maternal and Infant Innate Immune Responses: A Pilot Study

BACKGROUND

Research has demonstrated that some vaccines may have effects on the immune system beyond their intended targets. These heterologous effects of vaccination occur through reprogramming of innate immune cells, resulting in enhanced cytokine responses to unrelated pathogens and have been observed most evidently following Bacillus Calmette-Guérin vaccination. Pregnant women in the United Kingdom are offered influenza and acellular pertussis (Tdap) vaccines to protect the mother and infant, respectively, from infection. Little is known about the potential heterologous effects of vaccines given during pregnancy on the maternal and infant immune systems.

OBJECTIVE

To investigate heterologous innate immune responses in mothers and infants from pertussis-vaccinated and pertussis/influenza double-vaccinated pregnancies compared with unvaccinated pregnancies, in a pilot cohort.

METHODS

In this pilot study, samples collected as part of 2 maternal immunization studies were utilized. Maternal and cord peripheral blood mononuclear cells (PBMCs) were collected at birth from women who had received both Tdap and influenza vaccination, only the Tdap vaccine or no vaccines during pregnancy. To further investigate the effect of influenza vaccination alone, PBMCs were collected from nonpregnant women before and after seasonal influenza vaccination. PBMCs were incubated with pattern recognition receptor (PRR) ligands, vaccine adjuvants or CRM197 for 24 hours and cytokine responses were quantified in supernatants by enzyme-linked immunosorbent assay.

RESULTS

PBMC from women who received both Tdap and influenza vaccines had reduced IL-1β, IL-6 and IL-8 cytokine responses to PRR ligand stimulation, compared with those from women who received Tdap alone. Maternal vaccine status during pregnancy did not impact cytokine responses to PRR stimulation in cord PBMCs. Seasonal influenza vaccination did not alter cytokine responses to PRR ligands in nonpregnant women.

CONCLUSIONS

Our pilot study suggests that PBMC from women receiving combined Tdap and influenza vaccination during pregnancy may have reduced in vitro cytokine responses to nonpertussis stimuli. Larger cohorts of mother-infant pairs need to be studied to confirm these findings, study the potential mechanisms and control for potential confounders.

The antiarrhythmic drugs amiodarone and dronedarone inhibit intoxication of cells with pertussis toxin

Pertussis toxin (PT) is a virulent factor produced by Bordetella pertussis, the causative agent of whooping cough. PT exerts its pathogenic effects by ADP-ribosylating heterotrimeric G proteins, disrupting cellular signaling pathways. Here, we investigate the potential of two antiarrhythmic drugs, amiodarone and dronedarone, in mitigating PT-induced cellular intoxication. After binding to cells, PT is endocytosed, transported from the Golgi to the endoplasmic reticulum where the enzyme subunit PTS1 is released from the transport subunit of PT. PTS1 is translocated into the cytosol where it ADP-ribosylates inhibitory α-subunit of G-protein coupled receptors (Gαi). We showed that amiodarone and dronedarone protected CHO cells and human A549 cells from PT-intoxication by analyzing the ADP-ribosylation status of Gαi. Amiodarone had no effect on PT binding to cells or in vitro enzyme activity of PTS1 but reduced the signal of PTS1 in the cell suggesting that amiodarone interferes with intracellular transport of PTS1. Moreover, dronedarone mitigated the PT-mediated effect on cAMP signaling in a cell-based bioassay. Taken together, our findings underscore the inhibitory effects of amiodarone and dronedarone on PT-induced cellular intoxication, providing valuable insights into drug repurposing for infectious disease management.

Pertussis toxin-dependent and -independent protection by Bordetella pertussis against influenza

Bacterial-viral co-infections are frequent, but their reciprocal effects are not well understood. Here, we examined the effect Bordetella pertussis infection and the role of pertussis toxin (PT) on influenza A virus (IAV) infection and disease. In C57BL/6J mice, prior nasal administration of virulent B. pertussis BPSM and PT-deficient BPRA provided effective and sustained protection from IAV-induced mortality. However, BPSM or BPRA administered together with purified PT (BPRA + PT) had a stronger protective effect on weight loss compared to BPRA alone, reduced the viral load, and induced IL-17A in the lungs. In IL-17-/- mice, BPSM- and BPRA + PT-mediated protection against viral replication was abolished, while BPSM, BPRA and BPRA + PT provided similar levels of protection against IAV-induced mortality and weight loss. In conclusion, B. pertussis infection protects against influenza by two mechanisms: one reducing viral replication depending on PT and IL-17, and the other, independently of PT and IL-17, resulting in protection against influenza disease without reducing the viral load.

The T4bSS of Legionella features a two-step secretion pathway with an inner membrane intermediate for secretion of transmembrane effectors

To promote intracellular survival and infection, Legionella spp. translocate hundreds of effector proteins into eukaryotic host cells using a type IV b protein secretion system (T4bSS). T4bSS are well known to translocate soluble as well as transmembrane domain-containing effector proteins (TMD-effectors) but the mechanisms of secretion are still poorly understood. Herein we investigated the secretion of hydrophobic TMD-effectors, of which about 80 were previously reported to be encoded by L. pneumophila. A proteomic analysis of fractionated membranes revealed that TMD-effectors are targeted to and inserted into the bacterial inner membranes of L. pneumophila independent of the presence of a functional T4bSS. While the T4bSS chaperones IcmS and IcmW were critical for secretion of all tested TMD-effectors, they did not influence inner membrane targeting of these proteins. As for soluble effector proteins, translocation of all investigated TMD-effectors depended on a C-terminal secretion signal. A deeper analysis of the TMD-effector SidF showed that this signal needed to be presented towards the cytoplasmic side of the inner membrane and that a small periplasmic loop was required for efficient translocation. We propose that strongly hydrophobic TMD-effectors are secreted in a two-step secretion process: Initially, an inner membrane intermediate is formed, that is extracted towards the cytoplasmic side, possibly by the help of the type IV coupling protein complex and subsequently secreted into eukaryotic host cells by the T4bSS core complex. Overall, our study highlights the amazing versatility of T4bSS to secrete soluble and TMD-effectors from different subcellular locations of the bacterial cell.

5-hydroxytryptamine 2C/1A receptors modulate the biphasic dose response of the head twitch response and locomotor activity induced by DOM in mice

RATIONALE

The phenylalkylamine hallucinogen (-)-2,5-dimethoxy-4-methylamphetamine (DOM) exhibits an inverted U-shaped dose-response curve for both head twitch response (HTR) and locomotor activity in mice. Accumulated studies suggest that HTR and locomotor hyperactivity induced by DOM are mainly caused by the activation of serotonin 5-hydroxytryptamine 2 A receptor (5-HT2A receptor). However, the mechanisms underlying the biphasic dose response of HTR and locomotor activity induced by DOM, particularly at high doses, remain unclear.

OBJECTIVES

The primary objective of this study is to investigate the modulation of 5-HT2A/2C/1A receptors in HTR and locomotor activity, while also exploring the potential receptor mechanisms underlying the biphasic dose response of DOM.

METHODS

In this study, we employed pharmacological methods to identify the specific 5-HT receptor subtypes responsible for mediating the biphasic dose-response effects of DOM on HTR and locomotor activity in C57BL/6J mice.

RESULTS

The 5-HT2A receptor selective antagonist (R)-[2,3-di(methoxy)phenyl]-[1-[2-(4-fluorophenyl)ethyl]piperidin-4-yl]methanol (M100907) (500 µg/kg, i.p.) fully blocked the HTR at every dose of DOM (0.615-10 mg/kg, i.p.) in C57BL/6J mice. M100907 (50 µg/kg, i.p.) decreased the locomotor hyperactivity induced by a low dose of DOM (0.625, 1.25 mg/kg, i.p.), but had no effect on the locomotor hypoactivity induced by a high dose of DOM (10 mg/kg) in C57BL/6J mice. The 5-HT2C antagonist 6-chloro-5-methyl-1-[(2-[2-methylpyrid-3yloxy]pyrid-5yl)carbamoyl]indoline (SB242084) (0.3, 1 mg/kg, i.p.) reduced the HTR induced by a dose of 2.5 mg/kg DOM, but did not affect the response to other doses. SB242084 (1 mg/kg, i.p.) significantly increased the locomotor activity induced by DOM (0.615-10 mg/kg, i.p.) in mice. The 5-HT1A antagonist N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]N-(2-pyridinyl) cyclohexane carboxamide maleate (WAY100635) (1 mg/kg, i.p.) increased both HTR and locomotor activity induced by DOM in mice. The 5-HT1A agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) (1 mg/kg, i.p.) significantly reduced both the HTR and locomotor activity induced by DOM in mice. Additionally, pretreatment with the Gαi/o inhibitor PTX (0.25 µg/mouse, i.c.v.) enhanced the HTR induced by DOM and attenuated the effect of DOM on locomotor activity in mice.

CONCLUSIONS

Receptor subtypes 5-HT2C and 5-HT1A are implicated in the inverted U-shaped dose-response curves of HTR and locomotor activity induced by DOM in mice. The biphasic dose-response function of HTR and locomotor activity induced by DOM has different mechanisms in mice.

Pertussis vaccination in adults in France: Overview and suggestions for improvement

In France, the goal of the pertussis vaccination program is to protect newborns. All infants are vaccinated under the program and then given booster shots up to the age of 25 years. Pregnant women are likewise vaccinated, with the cocooning strategy reserved for infants born to unvaccinated mothers. Real-world data shows (i) inadequate coverage among adolescents and adults under 25; (ii) improper use of the tetanus, diphtheria, and polio (Td/IPV) vaccine in children under six years, adolescents, and young adults; and (iii) underdiagnosis of pertussis in adults. Older patients or those with specific chronic medical conditions are at risk of developing severe disease. Improving the diagnosis and surveillance of pertussis in adults and seniors would be one of the first steps in the right direction. Aligning pertussis vaccination in adults with the Td/IPV program (boosters at 45, 65 years of age, and then every 10 years) would make the vaccination schedule simpler, easier to understand, and easier to implement. Large-scale awareness campaigns targeting this population would increase coverage, thereby boosting the effectiveness of the other measures.

Immunization with an mRNA DTP vaccine protects against pertussis in rats

Bordetella pertussis is a Gram-negative bacterium that is the causative agent of the respiratory disease known as pertussis. Since the switch to the acellular vaccines of DTaP and Tap, pertussis cases in the US have risen and cyclically fallen. We have observed that mRNA pertussis vaccines are immunogenic and protective in mice. Here, we further evaluated the pertussis toxoid mRNA antigen and refined the formulation based on optimal pertussis toxin neutralization in vivo. We next evaluated the mRNA pertussis vaccine in Sprague-Dawley rats using an aerosol B. pertussis challenge model paired with whole-body plethysmography to monitor coughing and respiratory function. Female Sprague-Dawley rats were primed and boosted with either commercially available vaccines (DTaP or wP-DTP), an mRNA-DTP vaccine, or mock-vaccinated. The mRNA-DTP vaccine was immunogenic in rats and induced antigen-specific IgG antibodies comparable to DTaP. Rats were then aerosol challenged with a streptomycin-resistant emerging clinical isolate D420Sm1. Bacterial burden was assessed at days 1 and 9 post-challenge, and the mRNA vaccine reduced burden equal to both DTaP and wP-DTP. Whole-body plethysmography revealed that mRNA-DTP vaccinated rats were well protected against coughing which was comparable to the non-challenged group. These data suggest that an mRNA-DTP vaccine is immunogenic in rats and provides protection against aerosolized B. pertussis challenge in Sprague-Dawley rats.

Cytochrome oxidase requirements in Bordetella reveal insights into evolution towards life in the mammalian respiratory tract

Little is known about oxygen utilization during infection by bacterial respiratory pathogens. The classical Bordetella species, including B. pertussis, the causal agent of human whooping cough, and B. bronchiseptica, which infects nearly all mammals, are obligate aerobes that use only oxygen as the terminal electron acceptor for electron transport-coupled oxidative phosphorylation. B. bronchiseptica, which occupies many niches, has eight distinct cytochrome oxidase-encoding loci, while B. pertussis, which evolved from a B. bronchiseptica-like ancestor but now survives exclusively in and between human respiratory tracts, has only three functional cytochrome oxidase-encoding loci: cydAB1, ctaCDFGE1, and cyoABCD1. To test the hypothesis that the three cytochrome oxidases encoded within the B. pertussis genome represent the minimum number and class of cytochrome oxidase required for respiratory infection, we compared B. bronchiseptica strains lacking one or more of the eight possible cytochrome oxidases in vitro and in vivo. No individual cytochrome oxidase was required for growth in ambient air, and all three of the cytochrome oxidases conserved in B. pertussis were sufficient for growth in ambient air and low oxygen. Using a high-dose, large-volume persistence model and a low-dose, small-volume establishment of infection model, we found that B. bronchiseptica producing only the three B. pertussis-conserved cytochrome oxidases was indistinguishable from the wild-type strain for infection. We also determined that CyoABCD1 is sufficient to cause the same level of bacterial burden in mice as the wild-type strain and is thus the primary cytochrome oxidase required for murine infection, and that CydAB1 and CtaCDFGE1 fulfill auxiliary roles or are important for aspects of infection we have not assessed, such as transmission. Our results shed light on the environment at the surface of the ciliated epithelium, respiration requirements for bacteria that colonize the respiratory tract, and the evolution of virulence in bacterial pathogens.

NAD activates olfactory receptor 1386 to regulate type I interferon responses in Plasmodium yoelii YM infection

Olfactory receptors (Olfr) are G protein-coupled receptors that are normally expressed on olfactory sensory neurons to detect volatile chemicals or odorants. Interestingly, many Olfrs are also expressed in diverse tissues and function in cell-cell recognition, migration, and proliferation as well as immune responses and disease processes. Here, we showed that many Olfr genes were expressed in the mouse spleen, linked to Plasmodium yoelii genetic loci significantly, and/or had genome-wide patterns of LOD scores (GPLSs) similar to those of host Toll-like receptor genes. Expression of specific Olfr genes such as Olfr1386 in HEK293T cells significantly increased luciferase signals driven by IFN-β and NF-κB promoters, with elevated levels of phosphorylated TBK1, IRF3, P38, and JNK. Mice without Olfr1386 were generated using the CRISPR/Cas9 method, and the Olfr1386-/- mice showed significantly lower IFN-α/β levels and longer survival than wild-type (WT) littermates after infection with P. yoelii YM parasites. Inhibition of G protein signaling and P38 activity could affect cyclic AMP-responsive element promoter-driven luciferase signals and IFN-β mRNA levels in HEK293T cells expressing the Olfr1386 gene, respectively. Screening of malaria parasite metabolites identified nicotinamide adenine dinucleotide (NAD) as a potential ligand for Olfr1386, and NAD could stimulate IFN-β responses and phosphorylation of TBK1 and STAT1/2 in RAW264.7 cells. Additionally, parasite RNA (pRNA) could significantly increase Olfr1386 mRNA levels. This study links multiple Olfrs to host immune response pathways, identifies a candidate ligand for Olfr1386, and demonstrates the important roles of Olfr1386 in regulating type I interferon (IFN-I) responses during malaria parasite infections.

Inhibitory G proteins play multiple roles to polarize sensory hair cell morphogenesis

Inhibitory G alpha (GNAI or Gαi) proteins are critical for the polarized morphogenesis of sensory hair cells and for hearing. The extent and nature of their actual contributions remains unclear, however, as previous studies did not investigate all GNAI proteins and included non-physiological approaches. Pertussis toxin can downregulate functionally redundant GNAI1, GNAI2, GNAI3, and GNAO proteins, but may also induce unrelated defects. Here, we directly and systematically determine the role(s) of each individual GNAI protein in mouse auditory hair cells. GNAI2 and GNAI3 are similarly polarized at the hair cell apex with their binding partner G protein signaling modulator 2 (GPSM2), whereas GNAI1 and GNAO are not detected. In Gnai3 mutants, GNAI2 progressively fails to fully occupy the sub-cellular compartments where GNAI3 is missing. In contrast, GNAI3 can fully compensate for the loss of GNAI2 and is essential for hair bundle morphogenesis and auditory function. Simultaneous inactivation of Gnai2 and Gnai3 recapitulates for the first time two distinct types of defects only observed so far with pertussis toxin: (1) a delay or failure of the basal body to migrate off-center in prospective hair cells, and (2) a reversal in the orientation of some hair cell types. We conclude that GNAI proteins are critical for hair cells to break planar symmetry and to orient properly before GNAI2/3 regulate hair bundle morphogenesis with GPSM2.

Alternate typhoid toxin assembly evolved independently in the two Salmonella species

AB5-type toxins are a diverse family of protein toxins composed of an enzymatic active (A) subunit and a pentameric delivery (B) subunit. Salmonella enterica serovar Typhi's typhoid toxin features two A subunits, CdtB and PltA, in complex with the B subunit PltB. Recently, it was shown that S. Typhi encodes a horizontally acquired B subunit, PltC, that also assembles with PltA/CdtB to produce a second form of typhoid toxin. S. Typhi therefore produces two AB5 toxins with the same A subunits but distinct B subunits, an evolutionary twist that is unique to typhoid toxin. Here, we show that, remarkably, the Salmonella bongori species independently evolved an analogous capacity to produce two typhoid toxins with distinct B subunits. S. bongori's alternate B subunit, PltD, is evolutionarily distant from both PltB and PltC and outcompetes PltB to form the predominant toxin. We show that, surprisingly, S. bongori elicits similar levels of CdtB-mediated intoxication as S. Typhi during infection of cultured human epithelial cells. This toxicity is exclusively due to the PltB toxin, and strains lacking pltD produce increased amounts of PltB toxin and exhibit increased toxicity compared to the wild type, suggesting that the acquisition of the PltD subunit potentially made S. bongori less virulent toward humans. Collectively, this study unveils a striking example of convergent evolution that highlights the importance of the poorly understood "two-toxin" paradigm for typhoid toxin biology and, more broadly, illustrates how the flexibility of A-B interactions has fueled the evolutionary diversification and expansion of AB5-type toxins.

IMPORTANCE

Typhoid toxin is an important Salmonella Typhi virulence factor and an attractive target for therapeutic interventions to combat typhoid fever. The recent discovery of a second version of this toxin has substantial implications for understanding S. Typhi pathogenesis and combating typhoid fever. In this study, we discover that a remarkably similar two-toxin paradigm evolved independently in Salmonella bongori, which strongly suggests that this is a critical aspect of typhoid toxin biology. We observe significant parallels between how the two toxins assemble and their capacity to intoxicate host cells during infection in S. Typhi and S. bongori, which provides clues to the biological significance of this unusual toxin arrangement. More broadly, AB5 toxins with diverse activities and mechanisms are essential virulence factors for numerous important bacterial pathogens. This study illustrates the capacity for novel A-B interactions to evolve and thus provides insight into how such a diverse arsenal of toxins might have emerged.

Overview of Bacterial Protein Toxins from Pathogenic Bacteria: Mode of Action and Insights into Evolution

Bacterial protein toxins are secreted by certain bacteria and are responsible for mild to severe diseases in humans and animals. They are among the most potent molecules known, which are active at very low concentrations. Bacterial protein toxins exhibit a wide diversity based on size, structure, and mode of action. Upon recognition of a cell surface receptor (protein, glycoprotein, and glycolipid), they are active either at the cell surface (signal transduction, membrane damage by pore formation, or hydrolysis of membrane compound(s)) or intracellularly. Various bacterial protein toxins have the ability to enter cells, most often using an endocytosis mechanism, and to deliver the effector domain into the cytosol, where it interacts with an intracellular target(s). According to the nature of the intracellular target(s) and type of modification, various cellular effects are induced (cell death, homeostasis modification, cytoskeleton alteration, blockade of exocytosis, etc.). The various modes of action of bacterial protein toxins are illustrated with representative examples. Insights in toxin evolution are discussed.

Direct interrogation of context-dependent GPCR activity with a universal biosensor platform

G protein-coupled receptors (GPCRs) are the largest family of druggable proteins encoded in the human genome, but progress in understanding and targeting them is hindered by the lack of tools to reliably measure their nuanced behavior in physiologically relevant contexts. Here, we developed a collection of compact ONE vector G-protein Optical (ONE-GO) biosensor constructs as a scalable platform that can be conveniently deployed to measure G-protein activation by virtually any GPCR with high fidelity even when expressed endogenously in primary cells. By characterizing dozens of GPCRs across many cell types like primary cardiovascular cells or neurons, we revealed insights into the molecular basis for G-protein coupling selectivity of GPCRs, pharmacogenomic profiles of anti-psychotics on naturally occurring GPCR variants, and G-protein subtype signaling bias by endogenous GPCRs depending on cell type or upon inducing disease-like states. In summary, this open-source platform makes the direct interrogation of context-dependent GPCR activity broadly accessible.

The T4bSS of Legionella features a two-step secretion pathway with an inner membrane intermediate for secretion of transmembrane effectors

To promote intracellular survival and infection, Legionella spp. translocate hundreds of effector proteins into eukaryotic host cells using a type IV b protein secretion system (T4bSS). T4bSS are well known to translocate soluble as well as transmembrane domain-containing effector proteins (TMD-effectors) but the mechanisms of secretion are still poorly understood. Herein we investigated the secretion of hydrophobic TMD-effectors, of which about 80 were previously reported to be encoded by L. pneumophila. A proteomic analysis of fractionated membranes revealed that TMD-effectors are targeted to and inserted into the bacterial inner membranes of L. pneumophila independent of the presence of a functional T4bSS. While the T4bSS chaperones IcmS and IcmW were critical for secretion of all tested TMD-effectors, they did not influence inner membrane targeting of these proteins. As for soluble effector proteins, translocation of TMD-effectors into host cells depended on a C-terminal secretion signal and this signal needed to be presented towards the cytoplasmic side of the inner membrane. A different secretion behavior of TMD- and soluble effectors and the need for small periplasmic loops within TMD-effectors provided strong evidence that TMD-effectors are secreted in a two-step secretion process: Initially, an inner membrane intermediate is formed, that is extracted towards the cytoplasmic side, possibly by the help of the type IV coupling protein complex and subsequently secreted into eukaryotic host cells by the T4bSS core complex. Overall, our study highlights the amazing versatility of T4bSS to secrete soluble and TMD-effectors from different subcellular locations of the bacterial cell.

Effects of free fatty acid receptor (FFAR) signaling on the modulation of cancer cell functions under hypoxic conditions

In the tumor environment, hypoxia promotes tumor progression, such as cancer cell growth, migration and chemoresistance. This study aimed to evaluate the roles of free fatty acid receptors (FFARs) in the regulation of cancer cell functions under hypoxic conditions, using fibrosarcoma HT1080 cells. HT1080 cells expressed FFAR1, FFAR2 and FFAR3 genes, but not FFAR4 gene. FFAR1, FFAR2 and FFAR3 expression levels in HT1080 cells cultured at 1 % O2 were elevated, compared with 21 % O2. The cell growth activities of HT1080 cells cultured at 21 % O2 were inhibited by acetic acid (AA) and propanoic acid (PA), but not 1 % O2. HT1080 cell motility was markedly reduced by culturing at 1 % O2. The cell growth and motility of HT1080 cells were enhanced by FFAR2 knockdown. The cell viability to cisplatin (CDDP) of HT1080 cells cultured at 1 % O2 was increased, compared with 21 % O2. FFAR2 knockdown suppressed the cell viability to CDDP of HT1080 cells. On the other hand, the cell motility and viability to CDDP of HT1080 cells cultured at 21 % O2 were suppressed by TUG-770. When HT1080 cells were cultured at 1 % O2, the cell motility and viability to CDDP were decreased, correlating with FFAR1 expression level. Moreover, FFAR1 knockdown increased the cell viability to CDDP of HT1080 cells cultured at 1 % O2. These results suggest that FFAR-mediated signaling plays an important role in the modulation of cellular functions of HT1080 cells under hypoxic conditions.

Inhibitory G proteins play multiple roles to polarize sensory hair cell morphogenesis

Inhibitory G alpha (GNAI or Gαi) proteins are critical for the polarized morphogenesis of sensory hair cells and for hearing. The extent and nature of their actual contributions remains unclear, however, as previous studies did not investigate all GNAI proteins and included non-physiological approaches. Pertussis toxin can downregulate functionally redundant GNAI1, GNAI2, GNAI3 and GNAO proteins, but may also induce unrelated defects. Here we directly and systematically determine the role(s) of each individual GNAI protein in mouse auditory hair cells. GNAI2 and GNAI3 are similarly polarized at the hair cell apex with their binding partner GPSM2, whereas GNAI1 and GNAO are not detected. In Gnai3 mutants, GNAI2 progressively fails to fully occupy the subcellular compartments where GNAI3 is missing. In contrast, GNAI3 can fully compensate for the loss of GNAI2 and is essential for hair bundle morphogenesis and auditory function. Simultaneous inactivation of Gnai2 and Gnai3 recapitulates for the first time two distinct types of defects only observed so far with pertussis toxin: 1) a delay or failure of the basal body to migrate off-center in prospective hair cells, and 2) a reversal in the orientation of some hair cell types. We conclude that GNAI proteins are critical for hair cells to break planar symmetry and to orient properly before GNAI2/3 regulate hair bundle morphogenesis with GPSM2.

Direct interrogation of context-dependent GPCR activity with a universal biosensor platform

G protein-coupled receptors (GPCRs) are the largest family of druggable proteins in the human genome, but progress in understanding and targeting them is hindered by the lack of tools to reliably measure their nuanced behavior in physiologically-relevant contexts. Here, we developed a collection of compact ONE vector G-protein Optical (ONE-GO) biosensor constructs as a scalable platform that can be conveniently deployed to measure G-protein activation by virtually any GPCR with high fidelity even when expressed endogenously in primary cells. By characterizing dozens of GPCRs across many cell types like primary cardiovascular cells or neurons, we revealed new insights into the molecular basis for G-protein coupling selectivity of GPCRs, pharmacogenomic profiles of anti-psychotics on naturally-occurring GPCR variants, and G-protein subtype signaling bias by endogenous GPCRs depending on cell type or upon inducing disease-like states. In summary, this open-source platform makes the direct interrogation of context-dependent GPCR activity broadly accessible.

The diverse landscape of AB5-type toxins

AB5-type toxins are a group of secreted protein toxins that are central virulence factors for bacterial pathogens such as Shigella dysenteriae, Vibrio cholerae, Bordetella pertussis, and certain lineages of pathogenic Escherichia coli and Salmonella enterica. AB5 toxins are composed of an active (A) subunit that manipulates host cell biology in complex with a pentameric binding/delivery (B) subunit that mediates the toxin's entry into host cells and its subsequent intracellular trafficking. Broadly speaking, all known AB5-type toxins adopt similar structural architectures and employ similar mechanisms of binding, entering and trafficking within host cells. Despite this, there is a remarkable amount of diversity amongst AB5-type toxins; this includes different toxin families with unrelated activities, as well as variation within families that can have profound functional consequences. In this review, we discuss the diversity that exists amongst characterized AB5-type toxins, with an emphasis on the genetic and functional variability within AB5 toxin families, how this may have evolved, and its impact on human disease.

Development and validation of capillary electrophoresis sodium dodecyl sulfate (CE-SDS) method for purity analysis of pertussis toxin, filamentous haemagglutinin and pertactin antigens

We report here the development and validation of CE-SDS method for purity analysis of Acellular Pertussis vaccine components viz. purified Pertussis toxin (PTx), purified Filamentous haemagglutinin (FHA), and Pertactinantigen (PRN). The method was found to be specific and showed excellent linearity at a concentration range of 15.62 µg/mL-1000 µg/mL for purified PTx, 31.25 µg/mL-1000 µg/mL for purified FHA, and 3.9 µg/mL-1000 µg/mL for PRN antigen. Method reported limit of quantification (LOQ) 31.25 µg/mL, 62.5 µg/mL, and 7.8 µg/mL for purified PTx, FHA, and PRN respectively. Method precision (repeatability and intermediate precision) for purity and molecular weight determination in product matrix was below 10% for all three proteins. Method comparability studies were performed with SDS-PAGE. CE-SDS demonstrated corroborating results with SDS-PAGE for the estimation of purity and molecular weight analysis. However, CE-SDS method exhibited better resolution capabilities for resolving all the sub-unit peaks of PTx and isoforms of purified FHA. CE-SDS method also demonstrated stability indicating potential and thus fits its intended purpose as an effective analytical tool for quality control of acellular pertussis-based vaccines.

Regulation of FGF2-induced proliferation by inhibitory GPCR in normal pituitary cells

Introduction

Intracellular communication is essential for the maintenance of the anterior pituitary gland plasticity. The aim of this study was to evaluate whether GPCR-Gαi modulates basic fibroblast growth factor (FGF2)-induced proliferative activity in normal pituitary cell populations.

Methods

Anterior pituitary primary cell cultures from Wistar female rats were treated with FGF2 (10ng/mL) or somatostatin analog (SSTa, 100nM) alone or co-incubated with or without the inhibitors of GPCR-Gαi, pertussis toxin (PTX, 500nM), MEK inhibitor (U0126, 100µM) or PI3K inhibitor (LY 294002, 10 μM).

Results

FGF2 increased and SSTa decreased the lactotroph and somatotroph BrdU uptak2e (p<0.05) whereas the FGF2-induced S-phase entry was prevented by SSTa co-incubation in both cell types, with these effects being reverted by PTX, U0126 or LY294002 pre-incubation. The inhibition of lactotroph and somatotroph mitosis was associated with a downregulation of c-Jun expression, a decrease of phosphorylated (p) ERK and pAKT. Furthermore, SSTa was observed to inhibit the S-phase entry induced by FGF2, resulting in a further increase in the number of cells in the G1 phase and a concomitant reduction in the number of cells in the S phases (p< 0.05), effects related to a decrease of cyclin D1 expression and an increase in the expression of the cell cycle inhibitors p27 and p21.

Discussion

In summary, the GPCR-Gαi activated by SSTa blocked the pro-proliferative effect of FGF2 in normal pituitary cells via a MEK-dependent mechanism, which acts as a mediator of both anti and pro-mitogenic signals, that may regulate the principal effectors of the G1 to S-phase transition.

Domperidone Inhibits Clostridium botulinum C2 Toxin and Bordetella pertussis Toxin

Bordetella pertussis toxin (PT) and Clostridium botulinum C2 toxin are ADP-ribosylating toxins causing severe diseases in humans and animals. They share a common translocation mechanism requiring the cellular chaperones Hsp90 and Hsp70, cyclophilins, and FK506-binding proteins to transport the toxins' enzyme subunits into the cytosol. Inhibitors of chaperone activities have been shown to reduce the amount of transported enzyme subunits into the cytosol of cells, thus protecting cells from intoxication by these toxins. Recently, domperidone, an approved dopamine receptor antagonist drug, was found to inhibit Hsp70 activity. Since Hsp70 is required for cellular toxin uptake, we hypothesized that domperidone also protects cells from intoxication with PT and C2. The inhibition of intoxication by domperidone was demonstrated by analyzing the ADP-ribosylation status of the toxins' specific substrates. Domperidone had no inhibitory effect on the receptor-binding or enzyme activity of the toxins, but it inhibited the pH-driven membrane translocation of the enzyme subunit of the C2 toxin and reduced the amount of PTS1 in cells. Taken together, our results indicate that domperidone is a potent inhibitor of PT and C2 toxins in cells and therefore might have therapeutic potential by repurposing domperidone to treat diseases caused by bacterial toxins that require Hsp70 for their cellular uptake.

Development of a droplet digital PCR for pertussis toxin locus copy number determination in a genetically-modified Bordetella pertussis strain

To improve pertussis toxin (PT) yield in B. pertussis strains for vaccine production a genetically-engineered strain (gdPT 191-134 strain) with a second copy of the genetically detoxified PT (gdPT) locus was developed. The consistency of the production and genetic stability of the strain when used for vaccine production must be established. We developed two simplex ddPCR assays with PCR systems for ptxA, the target gene present in two copies, and pgm, the reference gene present as a single copy. The ddPCR assay had sufficient precision to discriminate the copy number of the PT locus accurately in two B. pertussis strains: one copy in the parent, non-genetically-engineered strain and two copies in the gdPT 191-134 strain. Using the ddPCR assays, we were able to show that the ratio of the ptxA to pgm genes decreased during serial culture passages, due to the loss of PT locus, which in turn, resulted in lower levels of PT production over time. We were then able to assess culture conditions that improved the stability of the double locus, as shown by non-significant reduction in gdPT toxin yield.

Effects of free fatty acid receptor-2 (FFAR2)-mediated signaling on the regulation of cellular functions in osteosarcoma cells

G protein coupled free fatty acid receptors (FFARs) are involved in the pathogenesis of several human diseases. FFAR2 and FFAR3 are activated by the binding of short-chain fatty acids (SCFAs). This study aimed to evaluate the roles of FFAR2 in the regulation of cellular functions in osteosarcoma HOS cells, using acetic acid and propanoic acid as FFAR2 and FFAR3 agonists. FFAR2 and FFAR3 genes were expressed in HOS cells. The cell motile activity of HOS cells was significantly stimulated by acetic acid and propanoic acid. In contrast, acetic acid and propanoic acid had no impact on the activation of matrix metalloproteinase-2 (MMP-2) and MMP-9. In cell survival assay, the cell survival rate to cisplatin (CDDP) of HOS cells was elevated by acetic acid and propanoic acid. To assess the effects of FFAR2 on cellular functions, FFAR2 knockdown (HOS-FFAR2) cells were generated from HOS cells. The cell motile activity of HOS-FFAR2 cells was enhanced by acetic acid and propanoic acid. In the presence of acetic acid and propanoic acid, MMP-2 and MMP-9 activities were reduced in HOS-FFAR2 cells, compared with control cells. When cells were treated with acetic acid and propanoic acid, the cell survival rate to CDDP of HOS-FFAR2 cells was significantly lower than that of control cells. These results suggest that activation of FFAR2-mediated signaling is involved in the modulation of cellular functions in HOS cells.

Pasteurian Contributions to the Study of Bordetella pertussis Toxins

As a tribute to Louis Pasteur on the occasion of the 200th anniversary of his birth, this article summarizes the main contributions of scientists from Pasteur Institutes to the current knowledge of toxins produced by Bordetella pertussis. The article therefore focuses on publications authored by researchers from Pasteur Institutes and is not intended as a systematic review of B. pertussis toxins. Besides identifying B. pertussis as the causative agent of whooping cough, Pasteurians have made several major contributions with respect to the structure–function relationship of the Bordetella lipo-oligosaccharide, adenylyl cyclase toxin and pertussis toxin. In addition to contributing to the understanding of these toxins’ mechanisms at the molecular and cellular levels and their role in pathogenesis, scientists at Pasteur Institutes have also exploited potential applications of the gathered knowledge of these toxins. These applications range from the development of novel tools to study protein–protein interactions over the design of novel antigen delivery tools, such as prophylactic or therapeutic vaccine candidates against cancer and viral infection, to the development of a live attenuated nasal pertussis vaccine. This scientific journey from basic science to applications in the field of human health matches perfectly with the overall scientific objectives outlined by Louis Pasteur himself.

A semi high-throughput whole blood-based flow cytometry assay to detect and monitor Bordetella pertussis-specific Th1, Th2 and Th17 responses

Introduction

The characterization of B. pertussis (Bp) antigen-specific CD4⁺ T cell cytokine responses should be included in the evaluation of immunogenicity of pertussis vaccines but is often hindered by the lack of standardized robust assays.

Methods

To overcome this limitation, we developed a two-step assay comprising a short-term stimulation of fresh whole blood with Bp antigens and cryopreservation of the stimulated cells, followed later on by batch-wise intracellular cytokine analysis by flow cytometry. Blood samples collected from recently acellular (aP) vaccine boosted subjects with a whole-cell- or aP-primed background was incubated for 24 hrs with Pertussis toxin, Filamentous hemagglutinin or a Bp lysate (400µl per stimulation). Antigen-specific IFN-γ-, IL-4/IL-5/IL-13-, IL-17A/IL-17F- and/or IL-22-producing CD4⁺ T cells were quantified by flow cytometry to reveal Th1, Th2, and Th17-type responses, respectively. The frequencies of IFN-γ-producing CD8⁺ T cells were also analyzed.

Results

We demonstrate high reproducibility of the Bp-specific whole blood intracellular staining assay. The results obtained after cryopreservation of the stimulated and fixed cells were very well correlated to those obtained without cryopreservation, an approach used in our previously published assay. Optimization resulted in high sensitivity thanks to very low non-specific backgrounds, with reliable detection of Bp antigen-specific Th1, Th2 and Th17-type CD4⁺ T cells, in the lowest range frequency of 0.01-0.03%. Bp antigen-specific IFN-γ⁺ CD8⁺ T lymphocytes were also detected. This test is easy to perform, analyse and interpret with the establishment of strict criteria defining Bp antigen responses.

Discussion

Thus, this assay appears as a promising test for evaluation of Bp antigen-specific CD4⁺ T cells induced by current and next generation pertussis vaccines.

Salmonella antibacterial Rhs polymorphic toxin inhibits translation through ADP-ribosylation of EF-Tu P-loop

Rearrangement hot spot (Rhs) proteins are members of the broad family of polymorphic toxins. Polymorphic toxins are modular proteins composed of an N-terminal region that specifies their mode of secretion into the medium or into the target cell, a central delivery module, and a C-terminal domain that has toxic activity. Here, we structurally and functionally characterize the C-terminal toxic domain of the antibacterial Rhsmain protein, TreTu, which is delivered by the type VI secretion system of Salmonella enterica Typhimurium. We show that this domain adopts an ADP-ribosyltransferase fold and inhibits protein synthesis by transferring an ADP-ribose group from NAD+ to the elongation factor Tu (EF-Tu). This modification is specifically placed on the side chain of the conserved D21 residue located on the P-loop of the EF-Tu G-domain. Finally, we demonstrate that the TriTu immunity protein neutralizes TreTu activity by acting like a lid that closes the catalytic site and traps the NAD+.

The evolutionary diversification of the Salmonella artAB toxin locus

Salmonella enterica is a diverse species of bacterial pathogens comprised of >2,500 serovars with variable host ranges and virulence properties. Accumulating evidence indicates that two AB₅-type toxins, typhoid toxin and ArtAB toxin, contribute to the more severe virulence properties of the Salmonella strains that encode them. It was recently discovered that there are two distinct types of artAB-like genetic elements in Salmonella: those that encode ArtAB toxins (artAB elements) and those in which the artA gene is degraded and the ArtB homolog, dubbed PltC, serves as an alternative delivery subunit for typhoid toxin (pltC elements). Here, we take a multifaceted approach to explore the evolutionary diversification of artAB-like genetic elements in Salmonella. We identify 7 subtypes of ArtAB toxins and 4 different PltC sequence groups that are distributed throughout the Salmonella genus. Both artAB and pltC are encoded within numerous diverse prophages, indicating a central role for phages in their evolutionary diversification. Genetic and structural analyses revealed features that distinguish pltC elements from artAB and identified evolutionary adaptations that enable PltC to efficiently engage typhoid toxin A subunits. For both pltC and artAB, we find that the sequences of the B subunits are especially variable, particularly amongst amino acid residues that fine tune the chemical environment of their glycan binding pockets. This study provides a framework to delineate the remarkably complex collection of Salmonella artAB/pltC-like genetic elements and provides a window into the mechanisms of evolution for AB₅-type toxins.

RGS12 polarizes the GPSM2-GNAI complex to organize and elongate stereocilia in sensory hair cells

Inhibitory G proteins (GNAI/Gαi) bind to the scaffold G protein signaling modulator 2 (GPSM2) to form a conserved polarity complex that regulates cytoskeleton organization. GPSM2 keeps GNAI in a guanosine diphosphate (GDP)-bound state, but how GPSM2-GNAI is generated or relates to heterotrimeric G protein signaling remains unclear. We find that RGS12, a GTPase-activating protein (GAP), is required to polarize GPSM2-GNAI at the hair cell apical membrane and to organize mechanosensory stereocilia in rows of graded heights. Accordingly, RGS12 and the guanine nucleotide exchange factor (GEF) DAPLE are asymmetrically co-enriched at the hair cell apical junction, and Rgs12 mouse mutants are deaf. GPSM2 and RGS12 share GoLoco motifs that stabilize GNAI(GDP), and GPSM2 outcompetes RGS12 to bind GNAI. Our results suggest that polarized GEF/GAP junctional activity might dissociate heterotrimeric G proteins, generating free GNAI(GDP) for GPSM2 at the adjacent apical membrane. GPSM2-GNAI(GDP), in turn, imparts asymmetry to the forming stereocilia to enable sensory function in hair cells.

Requirement of Peptidyl-Prolyl Cis/Trans isomerases and chaperones for cellular uptake of bacterial AB-type toxins

Bacterial AB-type toxins are proteins released by the producing bacteria and are the causative agents for several severe diseases including cholera, whooping cough, diphtheria or enteric diseases. Their unique AB-type structure enables their uptake into mammalian cells via sophisticated mechanisms exploiting cellular uptake and transport pathways. The binding/translocation B-subunit facilitates binding of the toxin to a specific receptor on the cell surface. This is followed by receptor-mediated endocytosis. Then the enzymatically active A-subunit either escapes from endosomes in a pH-dependent manner or the toxin is further transported through the Golgi to the endoplasmic reticulum from where the A-subunit translocates into the cytosol. In the cytosol, the A-subunits enzymatically modify a specific substrate which leads to cellular reactions resulting in clinical symptoms that can be life-threatening. Both intracellular uptake routes require the A-subunit to unfold to either fit through a pore formed by the B-subunit into the endosomal membrane or to be recognized by the ER-associated degradation pathway. This led to the hypothesis that folding helper enzymes such as chaperones and peptidyl-prolyl cis/trans isomerases are required to assist the translocation of the A-subunit into the cytosol and/or facilitate their refolding into an enzymatically active conformation. This review article gives an overview about the role of heat shock proteins Hsp90 and Hsp70 as well as of peptidyl-prolyl cis/trans isomerases of the cyclophilin and FK506 binding protein families during uptake of bacterial AB-type toxins with a focus on clostridial binary toxins Clostridium botulinum C2 toxin, Clostridium perfringens iota toxin, Clostridioides difficile CDT toxin, as well as diphtheria toxin, pertussis toxin and cholera toxin.

Pertussis toxin suppresses dendritic cell-mediated delivery of B. pertussis into lung-draining lymph nodes

The adenylate cyclase (ACT) and the pertussis (PT) toxins of Bordetella pertussis exert potent immunomodulatory activities that synergize to suppress host defense in the course of whooping cough pathogenesis. We compared the mouse lung infection capacities of B. pertussis (Bp) mutants (Bp AC⁻ or Bp PT^–) producing enzymatically inactive toxoids and confirm that ACT action is required for maximal bacterial proliferation in the first days of infection, whereas PT action is crucial for persistence of B. pertussis in mouse lungs. Despite accelerated and near complete clearance from the lungs by day 14 of infection, the PT⁻ bacteria accumulated within the lymphoid tissue of lung-draining mediastinal lymph nodes (mLNs). In contrast, the wild type or AC⁻ bacteria colonized the lungs but did not enter into mLNs. Lung infection by the PT⁻ mutant triggered an early arrival of migratory conventional dendritic cells with associated bacteria into mLNs, where the PT⁻ bacteria entered the T cell-rich paracortex of mLNs by day 5 and proliferated in clusters within the B-cell zone (cortex) of mLNs by day 14, being eventually phagocytosed by infiltrating neutrophils. Finally, only infection by the PT⁻ bacteria triggered an early production of anti-B. pertussis serum IgG antibodies already within 14 days of infection. These results reveal that action of the pertussis toxin blocks DC-mediated delivery of B. pertussis bacteria into mLNs and prevents bacterial colonization of mLNs, thus hampering early adaptive immune response to B. pertussis infection.

Of the three classical Bordetella species causing respiratory infections in mammals, only the human-specialized whooping cough agent B. pertussis produces the pertussis toxin (PT) as its major virulence factor. Human pertussis is an acute respiratory illness and the pleiotropic activities of pertussis toxin account for the characteristic systemic manifestations of the disease, such as hyperleukocytosis, histamine sensitization, hyperinsulinemia, or inflammatory lung pathology. We found that PT activity inhibits the migration of infected dendritic cells from the lungs into the draining mediastinal lymph nodes (mLNs). This prevents mLN infection by bacteria evading from migratory cells and delivery of bacterial antigens into mLNs. As a result, the induction of adaptive serum antibody responses to infection is delayed. We thus propose that PT action serves to create a time window for proliferation of B. pertussis on airway mucosa to facilitate transmission of the pathogen among humans.

Bacterial protein secretion systems: Game of types

Protein trafficking across the bacterial envelope is a process that contributes to the organisation and integrity of the cell. It is the foundation for establishing contact and exchange between the environment and the cytosol. It helps cells to communicate with one another, whether they establish symbiotic or competitive behaviours. It is instrumental for pathogenesis and for bacteria to subvert the host immune response. Understanding the formation of envelope conduits and the manifold strategies employed for moving macromolecules across these channels is a fascinating playground. The diversity of the nanomachines involved in this process logically resulted in an attempt to classify them, which is where the protein secretion system types emerged. As our knowledge grew, so did the number of types, and their rightful nomenclature started to be questioned. While this may seem a semantic or philosophical issue, it also reflects scientific rigour when it comes to assimilating findings into textbooks and science history. Here I give an overview on bacterial protein secretion systems, their history, their nomenclature and why it can be misleading for newcomers in the field. Note that I do not try to suggest a new nomenclature. Instead, I explore the reasons why naming could have escaped our control and I try to reiterate basic concepts that underlie protein trafficking cross membranes.

The Fim and FhaB adhesins play a crucial role in nasal cavity infection and Bordetella pertussis transmission in a novel mouse catarrhal infection model

Pulmonary infections caused by Bordetella pertussis used to be the prime cause of infant mortality in the pre-vaccine era and mouse models of pertussis pneumonia served in characterization of B. pertussis virulence mechanisms. However, the biologically most relevant catarrhal disease stage and B. pertussis transmission has not been adequately reproduced in adult mice due to limited proliferation of the human-adapted pathogen on murine nasopharyngeal mucosa. We used immunodeficient C57BL/6J MyD88 KO mice to achieve B. pertussis proliferation to human-like high counts of 108 viable bacteria per nasal cavity to elicit rhinosinusitis accompanied by robust shedding and transmission of B. pertussis bacteria to adult co-housed MyD88 KO mice. Experiments with a comprehensive set of B. pertussis mutants revealed that pertussis toxin, adenylate cyclase toxin-hemolysin, the T3SS effector BteA/BopC and several other known virulence factors were dispensable for nasal cavity infection and B. pertussis transmission in the immunocompromised MyD88 KO mice. In contrast, mutants lacking the filamentous hemagglutinin (FhaB) or fimbriae (Fim) adhesins infected the nasal cavity poorly, shed at low levels and failed to productively infect co-housed MyD88 KO or C57BL/6J mice. FhaB and fimbriae thus appear to play a critical role in B. pertussis transmission. The here-described novel murine model of B. pertussis-induced nasal catarrh opens the way to genetic dissection of host mechanisms involved in B. pertussis shedding and to validation of key bacterial transmission factors that ought to be targeted by future pertussis vaccines.

Aluminum hydroxide adjuvant diverts the uptake and trafficking of genetically detoxified pertussis toxin to lysosomes in macrophages

Aluminum salts have been successfully utilized as adjuvants to enhance the immunogenicity of vaccine antigens since the 1930s. However, the cellular mechanisms behind the immune adjuvanticity effect of these materials in antigen‐presenting cells are poorly understood. In this study, we investigated the uptake and trafficking of aluminum oxy‐hydroxide (AlOOH), in RAW 264.7 murine and U‐937 human macrophages‐like cells. Furthermore, we determined the impact that the adsorption to AlOOH particulates has on the trafficking of a Bordetella pertussis vaccine candidate, the genetically detoxified pertussis toxin (gdPT). Our results indicate that macrophages internalize AlOOH by constitutive macropinocytosis assisted by the filopodial protrusions that capture the adjuvant particles. Moreover, we show that AlOOH has the capacity to nonspecifically adsorb IgG, engaging opsonic phagocytosis, which is a feature that may allow for more effective capture and uptake of adjuvant particles by antigen‐presenting cells (APCs) at the site of vaccine administration. We found that AlOOH traffics to endolysosomal compartments that hold degradative properties. Importantly, while we show that gdPT escapes degradative endolysosomes and traffics toward the retrograde pathway, as reported for the wild‐type pertussis toxin, the adsorption to AlOOH diverts gdPT to traffic to the adjuvant’s lysosome‐type compartments, which may be key for MHC‐II‐driven antigen presentation and activation of CD4⁺ T cell. Thus, our findings establish a direct link between antigen adsorption to AlOOH and the intracellular trafficking of antigens within antigen‐presenting cells and bring to light a new potential mechanism for aluminum adjuvancy. Moreover, the in‐vitro single‐cell approach described herein provides a general framework and tools for understanding critical attributes of other vaccine formulations.

Novel Strategies to Inhibit Pertussis Toxin

Pertussis, also known as whooping cough, is a respiratory disease caused by infection with Bordetella pertussis, which releases several virulence factors, including the AB-type pertussis toxin (PT). The characteristic symptom is severe, long-lasting paroxysmal coughing. Especially in newborns and infants, pertussis symptoms, such as leukocytosis, can become life-threatening. Despite an available vaccination, increasing case numbers have been reported worldwide, including Western countries such as Germany and the USA. Antibiotic treatment is available and important to prevent further transmission. However, antibiotics only reduce symptoms if administered in early stages, which rarely occurs due to a late diagnosis. Thus, no causative treatments against symptoms of whooping cough are currently available. The AB-type protein toxin PT is a main virulence factor and consists of a binding subunit that facilitates transport of an enzyme subunit into the cytosol of target cells. There, the enzyme subunit ADP-ribosylates inhibitory α-subunits of G-protein coupled receptors resulting in disturbed cAMP signaling. As an important virulence factor associated with severe symptoms, such as leukocytosis, and poor outcomes, PT represents an attractive drug target to develop novel therapeutic strategies. In this review, chaperone inhibitors, human peptides, small molecule inhibitors, and humanized antibodies are discussed as novel strategies to inhibit PT.

In Vivo Metabolic Roles of G Proteins of the Gi Family Studied With Novel Mouse Models

G protein-coupled receptors (GPCRs) are the target of ~30% to 35% of all US Food and Drug Administration-approved drugs. The individual members of the GPCR superfamily couple to 1 or more functional classes of heterotrimeric G proteins. The physiological outcome of activating a particular GPCR in vivo depends on the pattern of receptor distribution and the type of G proteins activated by the receptor. Based on the structural and functional properties of their α-subunits, heterotrimeric G proteins are subclassified into 4 major families: Gs, Gi/o, Gq/11, and G12/13. Recent studies with genetically engineered mice have yielded important novel insights into the metabolic roles of Gi/o-type G proteins. For example, recent data indicate that Gi signaling in pancreatic α-cells plays a key role in regulating glucagon release and whole body glucose homeostasis. Receptor-mediated activation of hepatic Gi signaling stimulates hepatic glucose production, suggesting that inhibition of hepatic Gi signaling could prove clinically useful to reduce pathologically elevated blood glucose levels. Activation of adipocyte Gi signaling reduces plasma free fatty acid levels, thus leading to improved insulin sensitivity in obese, glucose-intolerant mice. These new data suggest that Gi-coupled receptors that are enriched in metabolically important cell types represent potential targets for the development of novel drugs useful for the treatment of type 2 diabetes and related metabolic disorders.

Budowa IV systemu sekrecji Legionella pneumophilai jego znaczenie w patogenezie

Bakterie Legionella pneumophila w środowisku naturalnym pasożytują wewnątrz komórek wybranych gatunków pierwotniaków, a po przedostaniu się do sztucznych systemów dystrybucji wody stają się ważnym czynnikiem etiologicznym zapalenia płuc u ludzi. Główną cechą determinującą patogenność tych bakterii jest zdolność do życia i replikacji w makrofagach płucnych, czyli w komórkach wyspecjalizowanych do fagocytozy, zabijania i trawienia mikroorganizmów. Warunkiem wstępnym rozwoju infekcji jest przełamanie mechanizmów bójczych makrofagów i utworzenie wakuoli replikacyjnej LCV (Legionella containing vacuole). Biogeneza wakuoli LCV jest możliwa dzięki sprawnemu funkcjonowaniu IV systemu sekrecji Dot/Icm, który jest wielobiałkowym, złożonym kompleksem umiejscowionym w wewnętrznej i zewnętrznej membranie osłony komórkowej bakterii. System Dot/Icm liczy 27 elementów, na które składają się m.in. kompleks rdzeniowo-transmembranowy, tworzący strukturalny szkielet całego systemu oraz kompleks białek sprzęgających. Geny kodujące komponenty systemu Dot/Icm są zorganizowane na dwóch regionach chromosomu bak-teryjnego. System sekrecji Dot/Icm umożliwia L. pneumophila wprowadzenie do cytozolu komórki gospodarza ponad 300 białek efektorowych, których skoordynowane działanie powoduje utrzymanie integralności błony wakuoli replikacyjnej oraz pozwala na manipulowanie różnymi procesami komórki. Ważnym elementem strategii wewnątrzkomórkowego namnażania się L. pneumophila jest modulowanie transportu pęcherzykowego, interakcja z retikulum endoplazmatycznym oraz zakłócenie biosyntezy białek, procesów autofagii i apoptozy komórki gospodarza. Poznanie złożonych mechanizmów regulacji i funkcji białek efektorowych systemu Dot/Icm ma decydujące znaczenie w zapobieganiu i leczeniu choroby legionistów.

Pathogenicity and virulence of Bordetella pertussis and its adaptation to its strictly human host

The highly contagious whooping cough agent Bordetella pertussis has evolved as a human-restricted pathogen from a progenitor which also gave rise to Bordetella parapertussis and Bordetella bronchiseptica. While the latter colonizes a broad range of mammals and is able to survive in the environment, B. pertussis has lost its ability to survive outside its host through massive genome decay. Instead, it has become a highly successful human pathogen by the acquisition of tightly regulated virulence factors and evolutionary adaptation of its metabolism to its particular niche. By the deployment of an arsenal of highly sophisticated virulence factors it overcomes many of the innate immune defenses. It also interferes with vaccine-induced adaptive immunity by various mechanisms. Here, we review data from invitro, human and animal models to illustrate the mechanisms of adaptation to the human respiratory tract and provide evidence of ongoing evolutionary adaptation as a highly successful human pathogen.

Bordetella Adenylate Cyclase Toxin Elicits Airway Mucin Secretion through Activation of the cAMP Response Element Binding Protein

The mucus layer protects airway epithelia from damage by noxious agents. Intriguingly, Bordetella pertussis bacteria provoke massive mucus production by nasopharyngeal epithelia during the initial coryza-like catarrhal stage of human pertussis and the pathogen transmits in mucus-containing aerosol droplets expelled by sneezing and post-nasal drip-triggered cough. We investigated the role of the cAMP-elevating adenylate cyclase (CyaA) and pertussis (PT) toxins in the upregulation of mucin production in B. pertussis-infected airway epithelia. Using human pseudostratified airway epithelial cell layers cultured at air–liquid interface (ALI), we show that purified CyaA and PT toxins (100 ng/mL) can trigger production of the major airway mucins Muc5AC and Muc5B. Upregulation of mucin secretion involved activation of the cAMP response element binding protein (CREB) and was blocked by the 666-15-Calbiochem inhibitor of CREB-mediated gene transcription. Intriguingly, a B. pertussis mutant strain secreting only active PT and producing the enzymatically inactive CyaA-AC^– toxoid failed to trigger any important mucus production in infected epithelial cell layers in vitro or in vivo in the tracheal epithelia of intranasally infected mice. In contrast, the PT^– toxoid-producing B. pertussis mutant secreting the active CyaA toxin elicited a comparable mucin production as infection of epithelial cell layers or tracheal epithelia of infected mice by the wild-type B. pertussis secreting both PT and CyaA toxins. Hence, the cAMP-elevating activity of B. pertussis-secreted CyaA was alone sufficient for activation of mucin production through a CREB-dependent mechanism in B. pertussis-infected airway epithelia in vivo.

In Vivo Models and In Vitro Assays for the Assessment of Pertussis Toxin Activity

One of the main virulence factors produced by Bordetella pertussis is pertussis toxin (PTx) which, in its inactivated form, is the major component of all marketed acellular pertussis vaccines. PTx ADP ribosylates Gα_i proteins, thereby affecting the inhibition of adenylate cyclases and resulting in the accumulation of cAMP. Apart from this classical model, PTx also activates some receptors and can affect various ADP ribosylation- and adenylate cyclase-independent signalling pathways. Due to its potent ADP-ribosylation properties, PTx has been used in many research areas. Initially the research primarily focussed on the in vivo effects of the toxin, including histamine sensitization, insulin secretion and leukocytosis. Nowadays, PTx is also used in toxicology research, cell signalling, research involving the blood–brain barrier, and testing of neutralizing antibodies. However, the most important area of use is testing of acellular pertussis vaccines for the presence of residual PTx. In vivo models and in vitro assays for PTx often reflect one of the toxin’s properties or details of its mechanism. Here, the established and novel in vivo and in vitro methods used to evaluate PTx are reviewed, their mechanisms, characteristics and limitations are described, and their application for regulatory and research purposes are considered.

A multilayered blood vessel/tumor tissue chip to investigate T cell infiltration into solid tumor tissues

Cancer immunotherapies based on the ability of T cells to recognize and kill tumor cells (TCs), including immune checkpoint blockade (ICB) therapy and chimeric antigen receptor (CAR) T cell therapy, have been greatly successful recently, but they are applicable for only a fraction of patients. One of the main challenges in cancer immunotherapy is the improvement of T cell infiltration into solid tumor tissues, as T cells can exert cytotoxicity against TCs only when they are in contact with TCs. T cells in the bloodstream infiltrate into solid tumor tissues by following two steps known as extravasation and interstitial migration. Herein, we developed a multilayered blood vessel/tumor tissue chip (MBTC) that allows systematic investigation on T cell tumor infiltration. The MBTC is composed of a top fluidic chamber, a porous membrane covered with an endothelial cell (EC) monolayer, and a collagen gel block encapsulating TCs. The full sequence of T cell tumor infiltration, including extravasation and interstitial migration, required for TC killing is demonstrated in the MBTCs: T cells applied through the top fluidic chamber of the MBTCs exhibited dynamic interactions with ECs for extravasation, including intraluminal crawling and transendothelial migration (TEM). After extravasation, T cells migrate toward TCs located at the bottom of a collagen block to kill them. Key characteristics of T cell dynamics in tumor microenvironments are recapitulated in the MBTCs: the vascular endothelial growth factor (VEGF) produced by TCs suppressed EC activation by inflammatory cytokines, or induced EC anergy, thereby significantly reducing T cell extravasation, whereas chemokines produced by TCs triggered T cell chemotaxis toward TCs. Anti-VEGF treatment in the MBTCs reverts EC anergy and promotes T cell infiltration, similar to the clinical effects of anti-VEGF. The MBTC is a useful model for pre-clinical evaluation of immunotherapeutics and the fundamental study of tumor immunology.

The Role of Formyl Peptide Receptors in Permanent and Low-Grade Inflammation: Helicobacter pylori Infection as a Model

Formyl peptide receptors (FPRs) are cell surface pattern recognition receptors (PRRs), belonging to the chemoattractant G protein-coupled receptors (GPCRs) family. They play a key role in the innate immune system, regulating both the initiation and the resolution of the inflammatory response. FPRs were originally identified as receptors with high binding affinity for bacteria or mitochondria N-formylated peptides. However, they can also bind a variety of structurally different ligands. Among FPRs, formyl peptide receptor-like 1 (FPRL1) is the most versatile, recognizing N-formyl peptides, non-formylated peptides, and synthetic molecules. In addition, according to the ligand nature, FPRL1 can mediate either pro- or anti-inflammatory responses. Hp(2-20), a Helicobacter pylori-derived, non-formylated peptide, is a potent FPRL1 agonist, participating in Helicobacter pylori-induced gastric inflammation, thus contributing to the related site or not-site specific diseases. The aim of this review is to provide insights into the role of FPRs in H. pylori-associated chronic inflammation, which suggests this receptor as potential target to mitigate both microbial and sterile inflammatory diseases.

Application of xCELLigence real-time cell analysis to the microplate assay for pertussis toxin induced clustering in CHO cells

The microplate assay with Chinese Hamster Ovary (CHO) cells is currently used as a safety test to monitor the residual pertussis toxin (PT) amount in acellular pertussis antigens prior to vaccine formulation. The assay is based on the findings that the exposure of CHO cells to PT results in a concentration-dependent clustering response which can be used to estimate the amount of PT in a sample preparation. A major challenge with the current CHO cell assay methodology is that scoring of PT-induced clustering is dependent on subjective operator visual assessment using light microscopy. In this work, we have explored the feasibility of replacing the microscopy readout for the CHO cell assay with the xCELLigence Real-Time Cell Analysis system (ACEA BioSciences, a part of Agilent). The xCELLigence equipment is designed to monitor cell adhesion and growth. The electrical impedance generated from cell attachment and proliferation is quantified via gold electrodes at the bottom of the cell culture plate wells, which is then translated into a unitless readout called cell index. Results showed significant decrease in the cell index readouts of CHO cells exposed to PT compared to the cell index of unexposed CHO cells. Similar endpoint concentrations were obtained when the PT reference standard was titrated with either xCELLigence or microscopy. Testing genetically detoxified pertussis samples unspiked or spiked with PT further supported the sensitivity and reproducibility of the xCELLigence assay in comparison with the conventional microscopy assay. In conclusion, the xCELLigence RTCA system offers an alternative automated and higher throughput method for evaluating PT-induced clustering in CHO cells.

Pharmacological targeting of host chaperones protects from pertussis toxin in vitro and in vivo

Whooping cough is caused by Bordetella pertussis that releases pertussis toxin (PT) which comprises enzyme A-subunit PTS1 and binding/transport B-subunit. After receptor-mediated endocytosis, PT reaches the endoplasmic reticulum from where unfolded PTS1 is transported to the cytosol. PTS1 ADP-ribosylates G-protein α-subunits resulting in increased cAMP signaling. Here, a role of target cell chaperones Hsp90, Hsp70, cyclophilins and FK506-binding proteins for cytosolic PTS1-uptake is demonstrated. PTS1 specifically and directly interacts with chaperones in vitro and in cells. Specific pharmacological chaperone inhibition protects CHO-K1, human primary airway basal cells and a fully differentiated airway epithelium from PT-intoxication by reducing intracellular PTS1-amounts without affecting cell binding or enzyme activity. PT is internalized by human airway epithelium secretory but not ciliated cells and leads to increase of apical surface liquid. Cyclophilin-inhibitors reduced leukocytosis in infant mouse model of pertussis, indicating their promising potential for developing novel therapeutic strategies against whooping cough.

A Mutation Upstream of the rplN-rpsD Ribosomal Operon Downregulates Bordetella pertussis Virulence Factor Production without Compromising Bacterial Survival within Human Macrophages

The BvgS/BvgA two-component system controls expression of ∼550 genes of Bordetella pertussis, of which, ∼245 virulence-related genes are positively regulated by the BvgS-phosphorylated transcriptional regulator protein BvgA (BvgA∼P). We found that a single G-to-T nucleotide transversion in the 5'-untranslated region (5'-UTR) of the rplN gene enhanced transcription of the ribosomal protein operon and of the rpoA gene and provoked global dysregulation of B. pertussis genome expression. This comprised overproduction of the alpha subunit (RpoA) of the DNA-dependent RNA polymerase, downregulated BvgA and BvgS protein production, and impaired production and secretion of virulence factors by the mutant. Nonetheless, the mutant survived like the parental bacteria for >2 weeks inside infected primary human macrophages and persisted within infected mouse lungs for a longer period than wild-type B. pertussis These observations suggest that downregulation of virulence factor production by bacteria internalized into host cells may enable persistence of the whooping cough agent in the airways.IMPORTANCE We show that a spontaneous mutation that upregulates transcription of an operon encoding ribosomal proteins and causes overproduction of the downstream-encoded α subunit (RpoA) of RNA polymerase causes global effects on gene expression levels and proteome composition of Bordetella pertussis Nevertheless, the resulting important downregulation of the BvgAS-controlled expression of virulence factors of the whooping cough agent did not compromise its capacity to persist for prolonged periods inside primary human macrophage cells, and it even enhanced its capacity to persist in infected mouse lungs. These observations suggest that the modulation of BvgAS-controlled expression of virulence factors may occur also during natural infections of human airways by Bordetella pertussis and may possibly account for long-term persistence of the pathogen within infected cells of the airways.

Innate and Adaptive Immune Responses against Bordetella pertussis and Pseudomonas aeruginosa in a Murine Model of Mucosal Vaccination against Respiratory Infection

Whole cell vaccines are frequently the first generation of vaccines tested for pathogens and can inform the design of subsequent acellular or subunit vaccines. For respiratory pathogens, administration of vaccines at the mucosal surface can facilitate the generation of a localized mucosal immune response. Here, we examined the innate and vaccine-induced immune responses to infection by two respiratory pathogens: Bordetella pertussis and Pseudomonas aeruginosa. In a model of intranasal administration of whole cell vaccines (WCVs) with the adjuvant curdlan, we examined local and systemic immune responses following infection. These studies showed that intranasal vaccination with a WCV led to a reduction of the bacterial burden in the airways of animals infected with the respective pathogen. However, there were unique changes in the cytokines produced, cells recruited, and inflammation at the site of infection. Both mucosal vaccinations induced antibodies that bind the target pathogen, but linear regression and principal component analysis revealed that protection from these pathogens is not solely related to antibody titer. Protection from P. aeruginosa correlated to a reduction in lung weight, blood lymphocytes and neutrophils, and the cytokines IL-6, TNF-α, KC/GRO, and IL-10, and promotion of serum IgG antibodies and the cytokine IFN-γ in the lung. Protection from B. pertussis infection correlated strongly with increased anti-B-pertussis serum IgG antibodies. These findings reveal valuable correlates of protection for mucosal vaccination that can be used for further development of both B. pertussis and P. aeruginosa vaccines.

Functional evidence for biased inhibition of G protein signaling by YM-254890 in human coronary artery endothelial cells

Small molecular chemicals targeting individual subtype of G proteins including Gs, Gi/o and Gq has been lacking, except for pertussis toxin being an established selective peptide inhibitor of the Gi/o protein. Recently, a cyclic depsipeptide compound YM-254890 isolated from culture broth of Chromobacterium sp. was reported as a selective inhibitor for the Gq protein by blocking GDP exchange of GTP on the α subunit of Gq complex. However, functional selectivity of YM-254890 towards various G proteins was not fully characterized, primarily due to its restricted availability before 2017. Here, using human coronary artery endothelial cells as a model, we performed a systemic pharmacological evaluation on the functional selectivity of YM-254890 on multiple G protein-mediated receptor signaling. First, we confirmed that YM-254890, at 30 nM, abolished UTP-activated P2Y₂ receptor-mediated Ca²⁺ signaling and ERK1/2 phosphorylation, indicating its potent inhibition on the Gq protein. However, we unexpectedly found that YM-254890 also significantly suppressed cAMP elevation and ERK1/2 phosphorylation induced by multiple Gs-coupled receptors including β₂-adrenegic, adenosine A₂ and PGI₂ receptors. Surprisingly, although YM-254890 had no impact on CXCR4/Gi/o protein-mediated suppression of cAMP production, it abolished ERK1/2 activation. Further, no cellular toxicity was observed for YM-254890, and it neither affected A23187- or thapsigargin-induced Ca²⁺ signaling, nor forskolin-induced cAMP elevation and growth factor-induced MAPK signaling. We conclude that YM-254890 is not a selective inhibitor for Gq protein; instead, it acts as a broad-spectrum inhibitor for Gq and Gs proteins and exhibits a biased inhibition on Gi/o signaling, without affecting non-GPCR-mediated cellular signaling.

UDP-glucose, a cellular danger signal, and nucleotide receptor P2Y14 enhance the invasion of human extravillous trophoblast cells

INTRODUCTION

P2Y14, one of the P2Y purinergic G-protein coupled receptors, is expressed in a variety of cells and tissues. Its ligand, UDP-glucose (UDPG), is released from damaged and stress-stimulated cells and acts as a danger signal via P2Y14. Thus, P2Y14 plays an important role in immunological defense systems. Here, we aimed to elucidate the expression, localization, and role of P2Y14 in human trophoblasts and the placenta.

METHODS

Human chorionic villus and placental tissues were subjected to immunostaining for P2Y14 protein and an extravillous trophoblast (EVT) marker, HLA-G. We examined the expression of P2Y14 and the effect of UDPG on cell proliferation and invasion in an EVT cell line, HTR-8/SVneo, using an MTS assay and a Transwell assay, respectively. We tested the effect of UDPG on cell invasion in P2Y14-underexpressing HTR-8/SVneo clones established by the lentiviral introduction of shRNA for P2RY14 mRNA.

RESULTS

Immunostaining revealed that P2Y14 was exclusively expressed by EVTs. P2RY14 mRNA and P2Y14 protein were expressed in HTR-8/SVneo cells. UDPG did not affect cell proliferation but it did enhance invasion. Inhibition of P2Y14 and decreasing the expression of P2Y14 suppressed UDPG-mediated invasive activity.

CONCLUSIONS

These results showed that EVT selectively expressed P2Y14 and that P2Y14 was positively involved in UDPG-enhanced EVT invasion. It suggests the possible existence of a danger signal-mediated physiological system at the fetomaternal interface where UDPG released from maternal tissues through destruction by EVT invasion may accelerate EVT invasion, allowing EVTs to undergo successful placentation and vascular remodeling.