Mechanisms of Asthma Protection by Microbial Agents

Abstract

Asthma is the most common chronic disease of childhood and global prevalence has increased significantly in recent decades, coinciding with a shift in exposure to microbes present in the environment. Our lab previously showed that airway administration of microbial agents, such as Amish farm dust extracts (AFDE) or the bacterial lysate OM-85 (Broncho-Vaxom), protects against experimental asthma and has profound transcriptional effects in an ovalbumin murine model of experimental asthma. However, transcriptional mechanisms underlying the asthma protective effects of AFDE and OM-85 require further investigation. The work described in this dissertation sought to characterize the cellular and transcriptional modifications induced in the lung by AFDE and OM-85 using an Alternaria alternata extract-induced experimental asthma mouse model. Considering the phenotypic similarities, a comparison was performed to determine whether AFDE and OM-85 confer asthma protection by similar changes in transcription. Lung function and bronchoalveolar lavage (BAL) cellularity were measured in BALB/c wild-type-mice treated intranasally (i.n.) with either AFDE or OM-85 in the presence or absence of Alternaria extracts. Lung tissue collected from these mice was used to perform flow cytometry, bulk RNA-seq, and single nucleus (sn)RNA-seq to profile and compare the responses to AFDE and OM-85. This work showed that the protection conferred by AFDE and OM-85 involves the differential expression of several shared genes. Both microbial agents suppress airway hyperresponsiveness (AHR) and eosinophilia, downregulate genes involved in type-2 inflammation, and induce a strong, activated, polyclonal B cell signal. Ongoing studies in B cell deficient mice seek to determine whether B cells are required for the asthma protective effects of AFDE.