Andrew J. Leishman

Tumour necrosis factor-α blockade suppresses murine allergic airways inflammation

Asthma is a heterogeneous disease that has been increasing in incidence throughout western societies and cytokines, including proinflammatory tumour necrosis factor alpha (TNF‐α), have been implicated in the pathogenesis of asthma. Anti‐TNF‐α therapies have been established successfully in the clinic for diseases such as rheumatoid arthritis and Crohns disease. TNF‐α‐blocking strategies are now being trialled in asthma; however, their mode of action is poorly understood. Based on the observation that TNF‐α induces lymph node hypertrophy we have attempted to investigate this as a mechanism of action of TNF‐α in airway inflammation by employing two models of murine airway inflammation, that we have termed short and long models, representing severe and mild/moderate asthma, respectively. The models differ by their immunization schedules. In the short model, characterized by eosinophilic and neutrophilic airway inflammation the effect of TNF‐α blockade was a reduction in draining lymph node (DLN) hypertrophy, eosinophilia, interleukin (IL)‐5 production and immunoglobulin E (IgE) production. In the long model, characterized by eosinophilic inflammation, TNF‐α blockade produced a reduction in DLN hypertrophy and IL‐5 production but had limited effects on eosinophilia and IgE production. These results indicate that anti‐TNF‐α can suppress DLN hypertrophy and decrease airway inflammation. Further investigations showed that anti‐TNF‐α‐induced inhibition of DLN hypertrophy cannot be explained by preventing l‐selectin‐dependent capture of lymphocytes into the DLN. Given that overall TNF blockade was able to suppress the short model (severe) more effectively than the long model (mild/moderate), the results suggest that TNF‐α blocking therapies may be more effective in the treatment of severe asthma.

Dissecting the contribution of innate and antigen-specific pathways to the breach of self-tolerance observed in a murine model of arthritis

Background: The relative roles of innate immunity and antigen-specific T cells in rheumatoid arthritis remain controversial. Previous studies demonstrated that T-helper type 1 cells of irrelevant antigen specificity (ovalbumin) induced a transient arthritis in BALB/c mice, which recapitulates many of the pre-articular and articular features of human disease and is associated with the emergence of autoreactive T and B-cell responses to joint-specific antigens. However, the mechanisms underlying this phenomenon were unclear. Objectives: The aim of this study was to dissect the relative contribution of innate and heterologous antigen-specific pathways to the breach of self-tolerance and pathology observed in this model and how this may result from modified T and B-cell interactions. Methods: To address this issue, experimental arthritis was elicited either by a non-specific inflammatory stimulus alone, by activation of T cells of an irrelevant specificity or a combination of both. Results: The non-specific inflammatory response generated by lipopolysaccharide led to articular inflammation and cartilage erosion, but did not break tolerance to joint-specific antigens. In contrast, local activation of T cells of an irrelevant specificity produced a similar pathological picture but, in addition, induced T-cell responses to unrelated joint-specific antigens with associated activation of autoreactive B cells. These effects could be further potentiated by the addition of lipopolysaccharide. Conclusion: These data demonstrate that non-specific inflammation alone is insufficient to breach self-tolerance. In contrast, T cells of an irrelevant specificity, when triggered locally in an antigen-specific manner, can breach self-tolerance leading to arthritis and autoantibody production, which can then be amplified in a non-specific manner.

Biological characterization of a novel class of toll‐like receptor 7 agonists designed to have reduced systemic activity

BACKGROUND AND PURPOSE Toll‐like receptor 7 (TLR7) agonists have potential in the treatment of allergic diseases. However, the therapeutic utility of current low molecular weight TLR7 agonists is limited by their systemic activity, resulting in unwanted side effects. We have developed a series of TLR7‐selective ‘antedrugs’, including SM‐324405 and AZ12441970, which contain an ester group rapidly cleaved in plasma to reduce systemic exposure.

TLR7 Stimulation of APCs Results in Inhibition of IL-5 through Type I IFN and Notch Signaling Pathways in Human Peripheral Blood Mononuclear Cells

TLR7 agonists modulate Th2 immune responses through mechanisms that have not been fully elucidated. Suppression of IL-5 production from Ag- or phytohemagglutinin-stimulated human PBMCs by the TLR7 antedrug AZ12441970 was mediated via type I IFN–dependent and type I IFN–independent mechanisms through TLR7 activation of plasmacytoid dendritic cells, B cells, and monocytes. The type I IFN–dependent inhibition of T cell–derived IL-5 was mediated by IFN-α acting directly on activated T cells. IL-10 was shown not to be involved in the type I IFN–independent inhibition of IL-5 and the mechanism of inhibition required cell–cell interaction. Notch signaling was implicated in the inhibition of IL-5, because addition of a γ-secretase inhibitor blocked the type I IFN–independent suppression of IL-5. Accordingly, AZ12441970 induced high levels of the notch ligands Dll1 and Dll4 mRNA, whereas immobilized DLL4 resulted in the suppression of IL-5 production. Therefore, we have elucidated two mechanisms whereby TLR7 agonists can modulate IL-5 production in human T cells. The suppression of Th2 cytokines, including IL-5, would be of benefit in diseases such as atopic asthma, so we assessed TLR7 function in PBMC from asthmatics and showed equivalent activity compared with healthy volunteers. Demonstrating this function is intact in asthmatics and knowing it links to suppression of Th2 cytokines support the case for developing such compounds for the treatment of allergic disease.

Mechanism of Action of Inhibition of Allergic Immune Responses by a Novel Antedrug TLR7 Agonist

Triggering innate immune responses through TLRs is expected to be a novel therapeutic strategy for the treatment of allergic diseases. TLR agonists are able to modulate Th2 immune responses through undefined mechanisms. We investigated the mechanism of action of the suppression of Th2 immune responses with a novel antedrug TLR7 agonist. The antedrug is rapidly metabolized by plasma esterases to an acid with reduced activity to limit systemic responses. Topical administration of this compound inhibited features of the allergic airway inflammatory response in rat and murine allergic airways model. Type I IFN played a role in the suppression of Th2 cytokines produced from murine splenocytes. Inhibition of Th2 immune responses with the antedrug TLR7 agonist was shown to be via a type I IFN–dependent mechanism following short-term exposure to the compound, although there might be type I IFN–independent mechanisms following long-term exposure. We have demonstrated that local type I IFN signaling and plasmacytoid dendritic cells, but not Th1 immune responses, are required for in vivo efficacy against murine airway Th2-driven eosinophilia. Furthermore, migration of dendritic cell subsets into the lung was related to efficacy and is dependent on type I IFN signaling. Thus, the mechanism of action at the cytokine and cellular level involved in the suppression of Th2 allergic responses has been characterized, providing a potential new approach to the treatment of allergic disease.

An investigation of the impact of the location and timing of antigen-specific T cell division on airways inflammation

It is widely accepted that allergic asthma is orchestrated by T helper type 2 lymphocytes specific for inhaled allergen. However, it remains unclear where and when T cell activation and division occurs after allergen challenge, and whether these factors have a significant impact on airways inflammation. We therefore employed a CD4‐T cell receptor transgenic adoptive transfer model in conjunction with laser scanning cytometry to characterize the location and timing of T cell division in asthma in vivo. Thus, for the first time we have directly assessed the division of antigen‐specific T cells in situ. We found that accumulation of divided antigen‐specific T cells in the lungs appeared to occur in two waves. The first very early wave was apparent before dividing T cells could be detected in the lymph node (LN) and coincided with neutrophil influx. The second wave of divided T cells accumulating in lung followed the appearance of these cells in LN and coincided with peak eosinophilia. Furthermore, accumulation of antigen‐specific T cells in the draining LN and lung tissue, together with accompanying pathology, was reduced by intervention with the sphingosine 1‐phosphate receptor agonist FTY720 2 days after challenge. These findings provide greater insight into the timing and location of antigen‐specific T cell division in airways inflammation, indicate that distinct phases and locations of antigen presentation may be associated with different aspects of pathology and that therapeutics targeted against leukocyte migration may be useful in these conditions.

CD4+ CD25+ regulatory T cells: a therapeutic target for liver diseases.

Background: Regulatory T cells (Tregs) have been shown to play an important role in maintaining peripheral immune homeostasis by suppressing autoreactive and allergen-specific T cells and turning off the immune response after the pathogen has been cleared. However, in certain situations Tregs can impair effective immunity to some pathogens and tumour cells. Objective: To review the role of Tregs in liver pathology and to assess the potential to enhance or inhibit their function as applied to the treatment of liver disease. Methods: The literature was reviewed using standard indexing terms and incorporating publications up to and including those published in 2007. Results/conclusions: Tregs are therapeutic targets for modulation in autoimmune disease and may provide new opportunities for application to human liver conditions.