Myocardial infarction (MI) occurs following acute thrombotic occlusion of a coronary artery, and triggers a robust inflammatory response. Within hours, neutrophils are recruited to the infarcted myocardium followed by the infiltration of pro-inflammatory Ly6Chi monocytes. Transition from the pro-inflammatory macrophage phenotype (M1) to an anti-inflammatory, pro-resolution phenotype (M2-like) is critical to successful infarct healing. Interventions that polarize macrophages towards an anti-inflammatory 'M2-like' phenotype improve infarct healing in the experimental MI mouse model and reduce subsequent adverse remodelling of the myocardium, but the endogenous mechanisms that regulate repair are not well understood. Furthermore, differences in the resolution of inflammation in C57BL/6 and BALB/c mice, which are two of the commonly used wild-type mouse strains in experimental MI have not been characterised. We previously found that low peripheral blood eosinophil count is associated with increased short-term risk of mortality in low-intermediate risk patients with ischaemic heart disease. This suggests that eosinophils may have a role in the successful remodelling and repair of the heart following myocardial infarction. Eosinophils express a number of immuno-modulating cytokines and lipid mediators implicated in the resolution of inflammation. Increasingly prominent is interleukin-4 (IL-4), a cytokine that has been found to maintain the anti-inflammatory M2-like phenotype in macrophages. We therefore hypothesised that IL-4Rα signalling and recruitment of eosinophils to the myocardium following infarction are key in regulating the subsequent inflammatory response and scar tissue formation during infarct repair and cardiac remodelling. Experimental MI was induced by permanent left anterior descending artery ligation in isofluorane anaesthetized 12-15 week-old male wild-type (WT) BALB/c, WT C57BL/6, IL4Rα-/-, IL-4Rαflox/-, IL-4Rαflox/-LysMCre mice and eosinophil-deficient ΔdblGATA mice. Cardiac function was characterised by high-resolution ultrasound and immune cell infiltration by flow cytometry of single cell infarct and remote zone tissue digests. Blood eosinophil count and 6-month all-cause mortality were assessed in 732 consecutive patients undergoing primary percutaneous coronary intervention for ST-segment elevation myocardial infarction (STEMI). The rate of mortality due to cardiac rupture was significantly higher in C57BL/6 mice in comparison with BALB/c mice at Day 7 post-MI. This was associated with a higher proportion of pro-inflammatory Ly-6Chi macrophages infiltrating the infarct zone tissue of C57BL/6 mice following MI. An accompanying reduction in the number of splenic Ly-6Chi monocytes post-MI, suggestive of splenic monocyte mobilisation, was seen in C57BL/6 mice but not found in BALB/c mice. Furthermore, C57BL/6 mice had a delayed transition in macrophage polarisation towards an anti-inflammatory phenotype. Disruption of IL4Rα signalling, in mice null for the IL4Rα gene, resulted in increased F4/80+ macrophage and pro-inflammatory Ly6Chi macrophage infiltration of the infarct zone and reduced expression of the anti-inflammatory macrophage marker CD206, compared to wild-type controls. Furthermore, expression of GATA3 and ST2, both associated with the immunosuppressive function of (CD4+ Foxp3+) regulatory T cells, was reduced in infarct zone regulatory T cells from IL4Rα-/- mice. These findings were associated with defective wound healing with impaired angiogenesis, increased scar size, disarrayed infarct zone collagen deposition, accompanied by modified expression of plod2 that encodes the collagen cross-linking enzyme lysyl hydroxylase 2. Resulting in greater left ventricular dilatation and loss of cardiac function, as well as a higher 7- day mortality due to cardiac rupture in IL4Rα-/- mice. This indicates that successful infarct repair requires the engagement of IL-4Rα signalling to facilitate the accumulation of anti-inflammatory macrophages and highly immunosuppressive ST2+ regulatory T cells in the heart following MI. Resident cardiac macrophages from naïve hearts of IL-4Rαflox/-LysMCre mice failed to undergo LysMCre-mediated deletion of the IL-4Rα gene, potentially because low or absent expression of Lyz2 (encoding lysozyme M). In both ST-elevation MI (STEMI) patients and mice after acute MI, there was a decline in peripheral blood eosinophil count, with activated eosinophils being recruited to the infarct zone and paracardial adipose tissue of mice. The transcription factors GATA-1 plays a role in the differentiation of eosinophils from eosinophil progenitor cells. Deletion of GATA-1 results in loss of the eosinophil lineage and has been exploited to develop the eosinophil-deficient ΔdblGATA mouse. ΔdblGATA mice were used to address the role of eosinophils in cardiac remodelling following MI. ΔdblGATA mice had increased left ventricular dilatation and reduced ejection fraction after induction of MI, relative to wild-type mice. ΔdblGATA mice had increased scar size with disarrayed infarct zone collagen deposition, accompanied by modified expression of the genes plod2 and lox, which are associated with collagen cross-linking. The proportion of CD206+ anti-inflammatory macrophages was less in the infarct zone of ΔdblGATA mice, but was restored by adoptive transfer of eosinophils from WT mice. Furthermore, adverse cardiac remodelling in eosinophil-deficient ΔdblGATA mice was rescued by provision of IL-4 complex following MI. In conclusion, an enhanced inflammatory response following MI underlies the increased risk of cardiac rupture seen with WT C57BL/6 mice in comparison to WT BALB/c mice. WT BALB/c mice are protected from cardiac rupture, which was associated with an absence of splenic monocyte mobilisation following ischaemic injury. The resolution of inflammation was found to be dependent on IL4Rα signalling which is crucial for cardiac repair and remodelling, through modulating inflammatory cell recruitment and phenotype, as well as scar formation. Eosinophils are recruited to the heart post-MI and are essential for regulating cardiac repair and remodelling, likely through provision of IL-4. Therefore, we were able to show that IL-4Rα signalling and recruitment of eosinophils to the myocardium following infarction are both key in regulating the subsequent inflammatory response and scar tissue formation during infarct healing and cardiac remodelling.

Background: According to recent studies in children, IgE sensitization not only against perennial allergens, but also against food allergens, is related to asthma risk and increased airway inflammation. During the last decade, a new technique for IgE determination based on allergen components has become available, but its use in epidemiological studies has been limited. Aims: To investigate the relationship between the pattern of IgE sensitization to allergen components and the prevalence of asthma, airway inflammation and hyperresponsiveness in a population-based setting. To examine the relationship of IgE sensitization to allergen extract, and airway inflammation, airway hyperresponsiveness and blood eosinophilia in asthmatics. To examine the natural history of IgE sensitization to food allergens in adults. To compare extract-based and component-based IgE measurements in relation with new-onset respiratory disease and airway inflammation and hyperresponsiveness. Methods: The present thesis is based on cross-sectional and longitudinal analyses of the adult, the population-based study ECRHS (European Community Health Survey) and a cross-sectional, observational study of young subjects with asthma. IgE sensitization was examined by means of both extract-based and component-based tests. Airway inflammation was assessed by exhaled NO and airway hyperresponsiveness with methacholine test. Results: IgE sensitization to food allergens independently related to increased airway inflammation in both a population-based study and a study of asthmatics. Furthermore, a relation was found with increased blood eosinophils in asthmatics. The decrease in prevalence of IgE sensitization against food allergens during a 9-year follow-up was larger than the decrease of aeroallergens. Subjects with IgE sensitization to both cat extract and components showed more frequent airway inflammation, greater bronchial responsiveness and higher likelihood of developing asthma and rhinitis than subjects with IgE sensitization only to cat extract. Conclusions: The presence of IgE antibodies against food allergens was independently associated with airway and systemic inflammation. Both aeroallergens and food allergens should be examined in order to understand the signaling of local and systemic inflammation in asthma. Prevalence of IgE sensitization to food decreased in adults to a larger extent than IgE sensitization against aeroallergens. Measurement of IgE sensitization to cat allergen components appears to have a higher clinical value than extract-based measurement