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Expression of cytokine genes during pneumococcal and nontypeable Haemophilus influenzae acute otitis media in the rat.

ABSTRACT: Acute otitis media (AOM) elicits potent inflammatory responses from the cells of the middle ear mucosa as well as from infiltrating leukocytes. To explore host responses during experimental AOM induced by Streptococcus pneumoniae type 3 and nontypeable Haemophilus influenzae (NTHi), otomicroscopy findings and expression of cytokine genes in the middle ear were monitored up to 1 month postinoculation. The mucosa and infiltrating cells responded rapidly to the bacterial challenge. Otomicroscopically, AOM appeared 1 day after NTHi inoculation and 3 days after pneumococcus inoculation. Pneumococcal AOM was more severe than NTHi otitis, but in general, lower transcript levels were detected in pneumococcus-infected than in NTHi-infected animals. Interleukin-6 (IL-6) mRNA levels peaked at 3 to 6 h for both pneumococcus-infected and NTHi-infected animals. IL-1alpha, tumor necrosis factor alpha, and IL-10 mRNA levels peaked at 6 h for NTHi otitis and 1 to 3 days for pneumococcal otitis. Comparing otomicroscopy with expression profiles, it would appear that the majority of cytokine mRNAs had passed their peak before the AOM diagnosis could be made clinically. Only transforming growth factor beta mRNA followed a slower time course, peaking very late and continuing expression even after the AOM was otomicroscopically resolved. IL-2 and IL-4 mRNAs were not detected in any animal at any time. Most of the investigated cytokines are very early markers for AOM and may be involved in initiation of inflammation, but they would be poor targets for pharmacological manipulation since their levels decline before clinical signs appear.

SUBMITTER: Melhus A

PROVIDER: S-EPMC101687 | biostudies-literature | 2000 Jul

REPOSITORIES: biostudies-literature

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Expression of cytokine genes during pneumococcal and nontypeable Haemophilus influenzae acute otitis media in the rat.

Melhus A A Ryan A F AF

Infection and immunity 20000701 7

Acute otitis media (AOM) elicits potent inflammatory responses from the cells of the middle ear mucosa as well as from infiltrating leukocytes. To explore host responses during experimental AOM induced by Streptococcus pneumoniae type 3 and nontypeable Haemophilus influenzae (NTHi), otomicroscopy findings and expression of cytokine genes in the middle ear were monitored up to 1 month postinoculation. The mucosa and infiltrating cells responded rapidly to the bacterial challenge. Otomicroscopical ...[more]

PMID: 10858218

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Project description:Nontypeable Haemophilus influenzae (NTHi) colonize the human pharynx asymptomatically, and are also an important cause of otitis media (OM). Previous studies have demonstrated that some genes are more prevalent in OM-causing NTHi strains than in commensal strains, suggesting a role in virulence. These studies, however, are unable to investigate the possible associations between gene polymorphisms and disease. This study examined amino acid polymorphisms and sequence diversity in a potential virulence gene, the hemin receptor hemR, from a previously characterized NTHi strain collection containing both commensal and OM organisms to identify possible associations between the polymorphisms and otitis media. The full open reading frame of hemR was sequenced from a total of 146 NTHi isolates, yielding a total of 47 unique HemR amino acid sequences. The predicted structure of HemR showed substantial similarity to a class of monomeric TonB dependent, ligand-gated channels involved in iron acquisition in other gram negative bacteria. Fifteen amino acid polymorphisms were significantly more prevalent at the 90% confidence level among commensal compared to OM isolates. Upon controlling for the confounding effect of population structure, over half of the polymorphism-otitis media relationships lost statistical significance, emphasizing the importance of assessing the effect of population structure in association studies. The seven polymorphisms that retained significance were dispersed throughout the protein in various functional and structural domains, including the signal peptide, N-terminal plug domain, and intra- and extracellular loops. The alternate amino acid of only one of these seven polymorphisms was more common among OM isolates, demonstrating a strong trend toward the consensus sequence among disease causing NTHi. We hypothesize that variability at these positions in HemR may result in a reduced ability to acquire iron, rendering NTHi with such versions of the gene less fit for survival in the middle ear environment.

Project description:UNLABELLED:Nontypeable Haemophilus influenzae (NTHi) is a Gram-negative, human-restricted pathogen. Although this bacterium typically colonizes the nasopharynx in the absence of clinical symptoms, it is also one of the major pathogens causing otitis media (OM) in children. Complement represents an important aspect of the host defense against NTHi. In general, NTHi is efficiently killed by complement-mediated killing; however, various resistance mechanisms have also evolved. We measured the complement resistance of NTHi isolates isolated from the nasopharynx and the middle ear fluids of OM patients. Furthermore, we determined the molecular mechanism of NTHi complement resistance. Complement resistance was strongly increased in isolates from the middle ear, which correlated with decreased binding of IgM. We identified a crucial role for the R2866_0112 gene in complement resistance. Deletion of this gene altered the lipooligosaccharide (LOS) composition of the bacterium, which increased IgM binding and complement-mediated lysis. In a novel mouse model of coinfection with influenza virus, we demonstrate decreased virulence for the R2866_0112 deletion mutant. These findings identify a mechanism by which NTHi modifies its LOS structure to prevent recognition by IgM and activation of complement. Importantly, this mechanism plays a crucial role in the ability of NTHi to cause OM. IMPORTANCE:Nontypeable Haemophilus influenzae (NTHi) colonizes the nasopharynx of especially young children without any obvious symptoms. However, NTHi is also a major pathogen in otitis media (OM), one of the most common childhood infections. Although this pathogen is often associated with OM, the mechanism by which this bacterium is able to cause OM is largely unknown. Our study addresses a key biological question that is highly relevant for child health: what is the molecular mechanism that enables NTHi to cause OM? We show that isolates collected from the middle ear fluid exhibit increased complement resistance and that the lipooligosaccharide (LOS) structure determines IgM binding and complement activation. Modification of the LOS structure decreased NTHi virulence in a novel NTHi-influenza A virus coinfection OM mouse model. Our findings may also have important implications for other Gram-negative pathogens harboring LOS, such as Neisseria meningitidis, Moraxella catarrhalis, and Bordetella pertussis.

Project description:A thorough understanding of the molecular details of the interactions between bacteria and host are critical to ultimately prevent disease. Recent technological advances allow simultaneous analysis of host and bacterial protein and metabolic profiles from a single small tissue sample to provide insight into pathogenesis. We used the chinchilla model of human otitis media to determine, for the first time, the most expansive delineation of global changes in protein and metabolite profiles during an experimentally induced disease. After 48 h of infection with nontypeable Haemophilus influenzae, middle ear tissue lysates were analyzed by high-resolution quantitative two-dimensional liquid chromatography-tandem mass spectrometry. Dynamic changes in 105 chinchilla proteins and 66 metabolites define the early proteomic and metabolomic signature of otitis media. Our studies indicate that establishment of disease coincides with actin morphogenesis, suppression of inflammatory mediators, and bacterial aerobic respiration. We validated the observed increase in the actin-remodeling complex, Arp2/3, and experimentally showed a role for Arp2/3 in nontypeable Haemophilus influenzae invasion. Direct inhibition of actin branch morphology altered bacterial invasion into host epithelial cells, and is supportive of our efforts to use the information gathered to modify outcomes of disease. The twenty-eight nontypeable Haemophilus influenzae proteins identified participate in carbohydrate and amino acid metabolism, redox homeostasis, and include cell wall-associated metabolic proteins. Quantitative characterization of the molecular signatures of infection will redefine our understanding of host response driven developmental changes during pathogenesis. These data represent the first comprehensive study of host protein and metabolite profiles in vivo in response to infection and show the feasibility of extensive characterization of host protein profiles during disease. Identification of novel protein targets and metabolic biomarkers will advance development of therapeutic and diagnostic options for treatment of disease.

Dataset Information

Expression of cytokine genes during pneumococcal and nontypeable Haemophilus influenzae acute otitis media in the rat.

Publications

Expression of cytokine genes during pneumococcal and nontypeable Haemophilus influenzae acute otitis media in the rat.

Similar Datasets

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