Airway Microbiome and Th17-mediated Inflammation in COPD Among HIV-infected Individuals in a Rural Ugandan Cohort

Introduction The improvement in access to antiretroviral therapy (ART) among people living with HIV/AIDs (PLWHA) has resulted in a decrease in HIV-associated morbidity and mortality[1]. This is particularly true in low- and middle-income countries (LMICs), which bear the largest burden of HIV[2]. The reduction in mortality has substantially increased life expectancy, with estimates among PLWHA now approaching that of the general population[3]. Consequently, there has been increased attention among survivors to the emerging burden of non-communicable diseases (NCD), such as chronic obstructive pulmonary disease (COPD)[4]. Sub-Saharan Africa, which has the highest density of PLWHA, has experienced dramatic increases in COPD related-morbidity and mortality especially in individuals with history of pulmonary tuberculosis (PTB)[5]. In rural Ugandan ART clinics, we reported COPD prevalence of 6.22% with history of PTB being the strongest predictor of COPD risk and reduced lung function[5]. Currently, it's not fully known what drives chronic lung inflammation in PLWHA population well-controlled on ART.

In search for answers to the above question, we have been exploring the role of altered airway microbiome in orchestrating chronic airway inflammation in PLWHA. Our research question has been supported by a growing body of knowledge from human and animal studies that alterations in the bacterial communities inhabiting the airway trigger immune responses and chronic airway inflammation[6-9]. In a recent study involving 50 HIV+COPD+, 50 HIV+COPD-, 50 HIV-COPD- and 50 HIV-COPD- participants in rural Uganda, we investigated the association between altered airway microbiome and HIV-associated COPD (NCT040702). Preliminary analysis from 16S sequencing on induced sputum samples revealed that, in spite of minor differences in bacterial diversity among PLHWA with COPD compared to controls, commensal microbes belonging to the genera Atopobium, Megasphaera, Actinomyces, Selenomonas, Stomatobaculum and Oribacterium were significantly enriched in PLWHA with COPD while microbes belonging to the genera Prevotella, Porphyromonas, Pseudopropionibacterium, Odoribacter and Filifactor were depleted. Our results clearly show that there are more lung bacteria impacted by HIV than COPD, suggesting that HIV-associated changes in unique airway microbial genera may be driving COPD among PLWHA in our cohort. Currently, what remains unknown is how such genera drive chronic airway inflammation.

Studies from mouse models report Prevotella, Bacteroides and Veillonella to play a significant role in orchestrating lung inflammation through Toll like receptor (TLR) 2/4 signaling on alveolar macrophages, epithelial cells and dendritic cells which prime cells of the adaptive immunity[8]. The reported outcome has been aberrant Th17 and reduced Treg immune responses using germ-free and specific pathogen-free mice models [8]. Similarly, recent evidence in human studies show that Prevotella and Veillonella genera are associated with a distinct metabolic profile, enhanced pro-inflammatory cytokine expression characterized by elevated Th17 cellular response[9]. Microbiome-host cell communication has been reported to be mediated by secreted bacterial outer membrane vesicles (OMVs), which correlate with bacterial biomass (figure 2) [8]. We believe that identifying airway bacterial genera which elicit aberrant Th17 response among PLWHA with COPD could be a stepping stone towards developing strategies aimed at restoring microbial balance either through direct elimination of pathobionts by antibiotics or restoration of commensals through probiotics to promote colonization resistance at mucosal surfaces.

Based on this background, we aim to investigate if airway microbiome fuels Th17 mediated airway inflammation in COPD among HIV-infected individuals. We hypothesize that: (1) microbiome induces airway Th17 and suppresses Treg immune responses among HIV-infected individuals with COPD; (2) bacterial-driven Th17 response promotes expression of pro-inflammatory genes among individuals with COPD and (3)airway microbiome mediates its effect on Th17 immune response through secretion of bacterial outer membrane vesicles (OMVs).

In this study, we will: (1) establish a relationship between airway microbiome and Th17/Treg cellular phenotypes among HIV-infected individuals with COPD; (2) investigate bacterial-mediated Th17 upregulation of pro-inflammatory and pro-fibrotic genes among HIV individuals with COPD and (3) explore the role of bacterial outer membrane vesicles (OMVs) in mediating microbiome driven Th17 immune responses among HIV individuals.