The role of immune tolerance and regulation in pneumococcal carriage and invasive disease.

Lead Research Organisation: University of Liverpool
Department Name: Institute of Infection and Global Health


Streptococcus pneumoniae (the pneumococcus) can cause a range of severe diseases such as pneumonia, meningitis and sepsis (blood poisoning) but it is also part of the normal community of microbes that live in our noses and throat. Therefore, it is very common to harbour the pneumococcus in our airways without suffering any signs or symptoms of disease. However, it is not understood how and why pneumococci spread from these areas into deeper tissues such as the lung or the brain where they cause disease or why the bacteria induce inflammation and strong immune responses in the lungs and brain but little, if any, response in our nose and throat. Understanding the "silent" infection of the upper airways is essential to understand how a normally safe organism can cause severe disease in a minority of individuals.

The pneumococcus accounts for around 2 million deaths per year, half of which occur in children under 5 years of age. This is more than HIV/AIDS, measles and malaria combined. The current vaccines against the pneumococcus provide excellent protection against a limited range of the circulating strains of the bacteria but there are concerns that replacement disease may occur as strains that are not covered by the vaccine start to colonise the environment of the upper airways made vacant by vaccination. We believe that this could be avoided by designing a vaccine that protects against pneumococcal diseases such as pneumonia and sepsis, but allows the bacteria to colonise normally in the upper airways, providing additional protection generated by natural immunity. We believe that the process of pneumococcal colonisation of the upper airways might be an important way of training our immune system to provide natural protection against pneumococcal disease. This route to natural immunity would be lost following vaccination with current vaccines that kill off upper airway bacteria. This may in turn leave us more vulnerable to pneumococcal disease caused by non-vaccine type strains.

This project aims to improve our understanding of the process of natural colonisation and persistence of Streptococcus pneumoniae in the upper airways. We aim to uncover the interaction of bacteria with host cells in the airways in order to understand how silent infection occurs. Finally, we will determine what factors (bacterial, host or environmental) that lead from upper airway infection to the development of invasive disease. Factors that may predispose us to pneumococcal disease include coinfection with other disease causing organisms, exposure to inhaled pollutants (cigarette smoke, car exhaust fumes etc.) or production of certain toxins by pneumococci. The data generated from this project will help us identify groups or individuals at particular risk of developing invasive pneumococcal disease and will inform the design of future, more effective pneumococcal vaccination strategies.

Technical Summary

The central aim of the proposal is to elucidate the host-pathogen interactions that lead to the development of stable asymptomatic nasopharyngeal carriage with the major human pathogen Streptococcus pneumoniae. Furthermore, we aim to examine the conditions (bacterial, host and environmental) that allow these interactions to become dysregulated prior to the onset of invasive disease. We will do this through use of in vitro models with airway epithelial cells, well established in vivo infection models and clinical studies linking in with a unique human experimental pneumococcal challenge (EHPC) model.
We have previously described a role for immunological tolerance in the establishment and maintance of pneumococcal carriage and in resistance to invasive pneumococcal disease. We will determine how pneumococci induce the production of transforming growth factor beta and the activity of T regulatory cells that is required for establishment of tolerance. We will examine the role of the pneumococcal toxin pneumolysin in induction of immunoregulation and determine whether additional contributions come from other pneumococcal virulence factors implicated in nasopharyngeal carriage. Additionally, we will explore how factors such as chronic infection with gastrointestinal nematodes or exposure to inhaled particulate pollutants can influence immune tolerance and predispose to invasive pneumococcal disease.
These aims will be achieved through mechanistic examination of pneumocccal-exposed primary airway epithelial cell cultures, use of clinically relevant in vivo models of pneumococcal nasopharyngeal carriage, and clinical studies determining the pattern of immune regulatory marker expression in pneumococcal carriers from different at-risk groups.

Planned Impact

Staff working on the research project will develop skills that will be transferrable to other sectors of the employment market including communication and interpersonal skills, organization, record keeping and statistical analysis skills. As the proposal will involve dealing with clinical samples, a course in Good Clinical Practice will be provided for all staff. The two post-doctoral scientists employed on the project would have the opportunity to focus on a major work programme over 5 years, an invaluable opportunity to produce papers, develop skills and enhance future career prospects. They would also develop laboratory skills in a number of key areas as the programme of work is multi-disciplinary.

This proposal will develop new and improved collaborations both within the UK (Liverpool with Manchester, Birmingham, UCL, University of London) and abroad (Liverpool with Hannover and Dublin). These collaborations will be across multidisciplinary research fields and will develop knowledge and skill sets for all involved.

Within the University of Liverpool, establishing a link between microbiologists at the Institute of Infection and Global Health and clinicians at the Liverpool School of Tropical Medicine and Liverpool University Hospitals (Royal and Aintree) will broaden knowledge for all parties involved. The novel combination of human in vitro cell culture, clinical studies and murine infection models will open up collaboration opportunities in the UK and abroad and data generated from the proposal will be used to secure further funding for the University through research grant applications.
The primary focus of the project is microbiology and immunology, and so academics in these areas will be the primary beneficiaries. However, workpackage 2 touches on issues that will be of interest to epidemiologists (impact of environment and coinfection). Although the proposal focuses on the pneumococcus, the approaches used and the interactions uncovered are likely to be of direct relevance to those working on other opportunistic commensal pathogens.

Clinicians, Healthcare Professionals and Industry
Data from this project will be of direct relevance to clinical researchers working on the control of pneumococcal disease. Within the 5 years of the project, emerging data on the relationship of natural pneumococcal carriage to invasive disease will aid clinical considerations around treatment of pneumococcal disease. In the longer term, based on the findings of our project, vaccine researchers, industry, clinicians and policy makers will benefit from adopting an alternative approach of designing novel pneumococcal vaccines that protect against invasive disease but allow natural carriage. Data generated as part of workpackages 2 and 3 should help identify groups or individuals who are at a high risk of developing invasive pneumococcal disease.

The Public
Within the duration of the grant we would benefit the public through promoting wider appreciation of the impact of pneumococcal disease in both the developed and the developing world. This would be achieved through publication of research findings in open access journals and with accompanying press releases in local and national press. Furthermore, talks, seminars and activity days organised at schools and in the community (libraries, museums etc.) would be arranged through the outreach organising committee within the Institute of Infection and Global Health. Workpackage 2 of this proposal focuses on the effects of pollution and smoking on susceptibility to pneumococcal disease. These issues are likely to be of particular interest to the public and so will be the focus of much of our outreach and media work. Further details of these and other impact activities can be found in the attached 'Pathways to Impact' file.


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Beentjes D (2022) Mechanistic Insights into the Impact of Air Pollution on Pneumococcal Pathogenesis and Transmission. in American journal of respiratory and critical care medicine

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Chaguza C (2020) Early Signals of Vaccine-driven Perturbation Seen in Pneumococcal Carriage Population Genomic Data. in Clinical infectious diseases : an official publication of the Infectious Diseases Society of America

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Chaguza C (2022) Comparative Genomics of Disease and Carriage Serotype 1 Pneumococci in Genome Biology and Evolution