Optimal regulation of immune responses is key for preserving body function. The goal of our lab is to understand cellular and molecular mechanisms promoting clearance of invading microorganisms and growing cancers, whilst at the same time preventing unwanted responses that lead to hypersensitive reactions or autoimmunity. Our work focuses on the following areas:
1. Local regulation of T cell responses during persistent viral infection
Understanding how some viral infections are easily cleared whereas others persist in our body is a current challenge in immunology. Some of these infections remain subclinical, but others pose a serious health challenge such as viral hepatitis, HIV and EBV. One of the mechanisms leading to viral persistence is called T cell exhaustion, in which virus-specific T cells “see” infected cells but fail at eradicating them because they become functionally impaired. We have developed a model to investigate viral persistence locally in the lung by instillation of clinically relevant adenovirus. The beauty of this system is that it is possible to quantify the progression of infection in a non-invasive manner by virtue of adenoviral luciferase expression (Fig. 1). In this model, we can observe a dose-dependent persistence of adenovirus for at least 90 days, which is accompanied by inflammation in the lung and accumulation of functionally impaired T cells lacking effector function. Manipulating the inflammatory response in the lung results in further expansion of anti-viral T cells, acquisition of effector mechanisms and viral clearance. Furthermore, persistent viral infection in the lung has a profound systemic effect because antiviral T cells are functionally impaired at distal sites like the skin, where adenoviruses are not detected. We are currently elucidating further cellular and molecular mechanisms that promote T cell impairment. Our studies may explain cellular and molecular mechanisms promoting functional impairment and may contribute to open new avenues to re-establish protective functions in antiviral T cells.
2. Immune regulation during allergic asthma
It is estimated that about 400 million people will be asthmatic by 2025 according to the WHO and the World Allergy Organization, with about 10% of children in North America being asthma sufferers. Currently there is no cure for asthma and therapy is limited to management of disease symptoms usually with corticosteroids. Our interest is to uderstand how effector cells such as eosinophils and allergen-specific CD4 T cells are locally regulated in the lung. For this, we have developed a technique to be able to precisely discriminate immune cells located in the lumen of the airways, lung interstitium and lung vasculature for detailed analysis by confocal microscopy (Fig. 2) and flow cytometry. We find that allergen is mostly present in dendritic cells (DCs) and macrophages that are positioned in the airway lumen. However, most interactions between DCs, allergen-specific CD4 T cells and eosinophils take place in the interstitial tissue, predominantly around bronchioli and larger blood vessels. These results suggest that there is an active and dynamic regulation of DCs and effector cells between the airway and interstitial compartments. We have observed that the magnitude of key functions of eosinophils (degranulation), CD4 T cells (degranulation and IL-13 production) and dendritic cells (CD4 T cell activation) differs depending on their location. We are currently studying the underlying mechanisms mediating positioning of eosinophils and CD4 T cells to specific lung compartments during the asthmatic response and how this regulates their pathological functions.
Fig. 2. Confocal microscopy analysis of the precise positioning of different immune cells in the lung during an allergic asthma reaction to house dust mite.
3. Self-recognition on dendritic cells enhances T cell awareness towards foreign antigen
Protective T cell responses against invading microorganisms are initiated soon after infection when typically the microbial load is relatively low. TCR affinity to its cognate MHC/peptide complex is an important factor dictating the sensitivity of an antigen-specific response by a particular T cell clone. We and others have shown that DC-T cell interactions during the steady state are crucial to maintain T cell antigen sensitivity. T cells recognise MHC/self-peptide complexes on resting DCs resulting in tonic TCR signalling and increased T cell sensitivity towards a subsequent challenge with foreign antigen (Figure 3). We are currently investigating how self-MHC recognition on DCs instructs the magnitude and quality of an antigen-specific T cell response in vivo. Our work is contributing to the understanding of how steady recognition of MHC/self-peptide complexes on peripheral DCs regulates the extent and type of T cell responses towards foreign antigen.
4. Protective cytotoxic T lymphocyte responses against influenza
Harnessing cytotoxic T lymphocyte (CTL) function against influenza is a promising strategy for protective vaccination because most immunodominant CTL epitopes are not altered across seasonal isolates of influenza virus. We are interested in understanding how CTLs protect the host against influenza by investigating the acquisition of effector mechanisms and memory function. We are elucidating the molecular cues instructing the positioning of CTLs in different lung compartments, i.e. intravascular, interstitium or airway lumen, and how these compartments imprint distinct functional properties on influenza-specific CTLs (Fig. 4). For this, we are using state of the art technologies such as in vivo differential labelling and 2-photon microscopy visualisation of CTLs and dendritic cells in the infected lung (Fig. 5).
Fig. 5. Two-photon live imaging of lung from mice infected with influenza. Shown is a bronchiolus infiltrated by dendritic cells (green) and virus-specific CTLs (red). Autofluorescence is shown in white.