Allergic reactions do not explain all the physiologic and clinical changes of asthma, however, an allergic background may increase responses to a second stimulus such as that seen during an infection. The interactions between allergic and infectious reactions may increase inflammation related to asthma. The overall hypothesis of this application is that the presence of a persistent Th2 inflammatory process, as seen in chronic asthma, enhances certain inflammatory and repair elements through primary suppression of prostaglandin (PG)-related pathways, while also inhibiting """"""""appropriate"""""""" up-regulation of these PG-pathways in response to a second/acute innate stimulus. We propose that reactions occurring at the level of the epithelium play a large role in these processes. The background reduction of PG-pathways by interleukin (IL)-13 serves to accentuate inflammatory responses to innate stimuli over that of the innate response alone by removing the regulatory PGE2 """"""""brake"""""""" on the system. We propose that these innate and Th2 processes (and their interactions) will be present and increased in asthma exacerbations, both at the level of tissue obtained from individuals dying of asthma (as compared to control groups), as well as in living asthmatics during an exacerbation of asthma. In order to investigate this hypothesis, we propose 3 specific aims.
Aim #1 will address the effects of the IL-13 background on primary human airway epithelial cells, specifically confirming the inhibition of PG-related pathways and addressing the role of this inhibition of PG-related pathways on induction of mucin (MUC5AC), inducible nitric oxide (iNOS), 15 lipoxygenase (LO) 1, IL-8 and matrix metalloproteinase (MMP)-1.
Aim #2 will add an innate stimulus (IL-1beta) to this Th2/IL-13 background in primary human epithelial cells to evaluate in vitro the interactions of innate stimuli on this Th2 background. In this aim, we will determine whether IL-13 limits the induction of PG- related pathways in response to innate stimuli. We will then evaluate the downstream impact of this inhibition to increase MUC5AC, iNOS, IL-8 and MMP-1 expression.
Aim #3 will determine whether there is evidence for both adaptive and innate factors/responses in vivo at the time of death from asthma in autopsy tissue and the relationship to evidence of infection. In living asthmatics with asthma exacerbations, we will prospectively evaluate whether 15S hydroxyeicosatetraenoic acid (HETE) and PGE2 (and their ratios) in induced sputum from exacerbating asthmatics 1) are predictive of infectious/innate related exacerbations, and 2) correlate with levels of IL-16/TNFa in sputum and exhaled nitric oxide (FENO). Finally, sputa from stable and exacerbating asthmatics will be added to primary epithelial cells to determine whether factors in sputa can recapitulate the findings of the addition of specific innate (IL-1beta) and adaptive (IL-13) factors to these cells. These three aims should provide new insights into how relationships between innate and adaptive/allergic immune responses influence inflammatory/repair, and finally clinical outcomes in chronic and acute asthma.
