Signaling Pathways in Eosinophils that Regulate Allergic Asthma and Inflammation
Open Access
- Author:
- Stokes, Kindra Nicole
- Graduate Program:
- Pathobiology
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- August 11, 2014
- Committee Members:
- Avery August, Dissertation Advisor/Co-Advisor
Margherita Teresa Anna Cantorna, Committee Chair/Co-Chair
Pamela Hankey Giblin, Committee Member
Curtis John Omiecinski, Committee Member
Sonia Angele Cavigelli, Special Member - Keywords:
- Eosinophils
Asthma
Allergy
Inflammation
STAT6
Itk
Btk
Microbiota - Abstract:
- Eosinophils are critical cellular mediators of Th2 responses in allergic asthma and airway inflammation. However, the signals that regulate their functions have not been well characterized. We have previously shown that eosinophil derived IL-13 plays an important role in the recruitment of T cells to the lung, and subsequent development of allergic asthma. We therefore tested the hypothesis that eosinophils are dependent upon signaling via the Th2 cytokine responsive transcription factor STAT6 signaling in the control of allergic airway inflammation. Using ΔdblGATA mice lacking eosinophils and transfer of STAT6-/- eosinophils, we found that unlike WT eosinophils, STAT6-/- eosinophils are unable to induce the development of allergic lung inflammation, including AHR, recruitment of CD4+ T cells, eosinophils and mucous production. By contrast, the absence of STAT6 in eosinophils does not affect their preformed cytokine expression, and there was no difference in homeostatic migration to spleen and peritoneal cavity under basal conditions in WT or STAT6-/- IL-5 transgenic mice. However, STAT6 was required for eosinophil recruitment to the lung during allergic lung inflammation, and for their chemotactic response to Eotaxin in vitro. These data indicate that like Th cells, eosinophils need to respond to Th2 cytokines via STAT6 during the development of allergic airway inflammation. Interleukin-2 inducible T cell kinase (Itk) and Bruton’s tyrosine kinase (Btk) are critical signal amplifiers that regulate lymphocyte and leukocyte development and function. However, the role of Itk and Btk in eosinophil function is unknown. Here we have tested the hypothesis that the Tec family kinases Itk and Btk regulate eosinophil function to control development of allergic airway inflammation. We show that Itk regulates eosinophil migration by controlling the downstream events of the CC chemokine receptor-3 (CCR3), which is critical for eosinophil chemotatic responsiveness and migration. Using ΔdblGATA mice lacking eosinophils and transfer of Itk-/- eosinophils, we found that eosinophils lacking Itk were unable to induce the development of AHR, although recruitment of CD4+ T cells to the lung was largely rescued. These data indicate that Itk not only regulates T cell responses, but that CCR3 signaling via Itk in eosinophils might affect the development of allergic asthma. By contrast, expression of Itk and Btk together negatively regulated eosinophils, resulting in enhanced responses in Itk/Btk double knockout out eosinophils. These studies indicate that eosinophil expression of Tec kinases Itk and Btk are integral in modulation of cytokine and chemokine signals during the development of airway allergic responses. Gastrointestinal eosinophils have been suggested to contribute to gut homeostatic conditions, however the mechanism by which lung and gut microbiota regulate eosinophils under Th2 conditions is unclear. The propensity for Th2 allergic responses and asthma has recently been linked to the dysbiosis of microbial colonization. Thus, the early establishment of microflora can potentially explain why some individuals are more predisposed to develop asthma and some do not. We hypothesize that the microbiota alters the requirement for eosinophil-mediated Th2 responses in during the initiation of allergic airway inflammation. We report that mice housed under “less-restricted specific-pathogen-free” (LR-SPF) conditions are protected against allergic asthma compared to mice house under “restricted specific-pathogen-free” (R-SPF) conditions. Moreover, 16s rRNA analysis of lung and fecal content reveal differences in lung microbiota diversity, suggesting a potential explanation for this phenomenon. Further, consistent with the “microbiota hypothesis”, reducing the microbiota in C57Bl/6 ΔdblGATA mice by antibiotic treatment resulted in enhanced susceptibility to developing allergic airway inflammation comparable to WT mice. Thus, we conclude that shifts in microbiota affect the requirement for eosinophil-mediated Th2 responses.