The role of Th17 immunity in pneumococcal disease

Pneumonia, meningitis and inner ear infections caused by the pneumococcus are a major cause of human illness and death. Current vaccines offer some protection but are not able to prevent disease caused by the wide range of different types of pneumococci. Recently, a new type of immune sys-tem cell (Th17 cell) has been identified which seems to promote immunity to all types of pneumococci. This research will aim to improve understanding of how this cell is involved this im-munity and how it could best be stimulated with a vaccine. The research will involve analysing immune cells in the blood of healthy volunteers and patients with recent pneumococcal infection to see if Th17 cells are present and how they behave. It will also investigate how Th17 cells can be stimulated in mice using pneumococcal proteins that have been previously identified as possible constituents of a vaccine. We will be particularly interested in how vaccines can induce protection against nasal colonisation by pneumococci since this is the first step in infection.

Background: Pneumococcal disease is a major human health problem. Current vaccines induce humoral immunity to capsular polysaccharide. However, protection is limited by the diversity of cap-sular serotypes. Recent evidence implicates the Th17 group of T lymphocytes in cell mediated, serotype-independent pneumococcal immunity.

Aim: To investigate the role of Th17 in pneumococcal immunity.

Objectives: 1. To characterise human Th17 and other T helper cell responses following infection with S. pneumoniae 2. To determine the role of pneumolysin (PLY) and IL-1? production in a) induc-tion of a Th17 response to pneumococci and b) recall responses in recolonised individuals 3. To determine the role of IL-22 in defence against pneumococci 4. To determine the optimal route and adjuvant to generate Th17 responses in the nasal mucosa following immunization with candidate pneumococcal vaccine targets.

Methods: 1. Blood samples will be collected from healthy volunteers of various ages, adult patients with positive blood cultures for S. pneumoniae and adult patients with positive blood cultures for Es-cherichia coli. Antigen presenting cells (APCs) will be infected with S. pneumoniae or exposed to various vaccine candidate proteins and the stimulated APCs will be co-cultured with memory CD4+ lymphocytes. Th17 development will be assayed by measuring the production of IL-17 and IL-22 by ELISA in supernatants and by intracellular staining for IL-17, IL-22 and Interferon- along with sur-face CD4 and analysis by flow cytometry. Results in healthy volunteers will be correlated with colonisation status. 2. The role of pneumolysin in inducing IL-1 secretion and inflammasome activa-tion will be investigated using cultured dendritic cells and macrophages and a murine colonisation model. NLRP3 knockout mice will be used to clarify the role of inflammasome activation in inducing a Th17 response. 3. Mice with inactivation of the IL-22 gene will be used in standard models of colonisation and infection with S. pneumoniae to determine the role of IL-22 in host defence against pneumococci. 4. Animals will be immunised with via intranasal, intradermal and intramuscular routes and the Th17 responses in nasal and splenic lymphoid tissue compared with that induced by nasopharyngeal colonisation with live S. pneumoniae.

Anticipated outcomes: This study will determine the role of Th17 cells and their associated cyto-kines in mucosal and systemic immune responses to S. pneumoniae. This will be important not only in improving understanding of how Th17 responses develop through infection but also for the future use of pneumococcal proteins in human vaccination.