The Biology of Regulatory T Cells in Human Allergen-Induced Asthma

Abstract

Regulatory T cells (Treg) are essential for the induction and maintenance of immunological tolerance to self and foreign antigens. The development of allergic asthma is mediated by T helper cell type-2 (Th2) inflammatory mechanisms and may also involve, based on murine and human studies of allergic asthma, compromised Treg immune regulation. Our overall objective was to more thoroughly elucidate the biology of Treg in allergic asthma, and to better understand their potential as a treatment for the disease. Initially, we characterized three different Treg phenotypes based on frequency and functional capacity. We showed both quantitative and functional heterogeneity in circulating Treg. Quantitative variability was also observed in circulating, but not airway, Treg when comparisons were made between healthy controls and asthmatic subjects. These findings emphasize the need for clear definitions of Treg phenotypes, and that interpretation of their frequency and function in health and disease needs to be phenotype-specific. Next, we assessed the Treg response in mild allergic asthmatic isolated early responders and dual responders after allergen inhalation challenge. We observed a reduced frequency of airway Treg after allergen challenge in DR, but not IER, associated with a smaller ratio of Treg to CD4+ cells. These data suggest that Treg to T effector cell (Teff) balance is important in the regulation of late asthmatic responses. Lastly, we evaluated the effects of two novel monoclonal anti-asthma therapies on circulating Treg after allergen inhalation challenge. We demonstrated that neither anti-OX40L nor anti-TSLP therapy altered circulating Treg frequency, while anti-TSLP, but not anti-OX40L, was effective in attenuating allergen-induced airway responses. These observations demonstrate the need for further investigation into the effects of anti-asthma therapies on Treg as well as the development of novel therapies aimed at manipulating Treg in order to better control immune responses. The findings of this thesis enhance our understanding of Treg in allergic asthma. Treg, utilized as stand-alone or adjunct therapy, may provide a novel therapy in the treatment of allergic asthma.