ABSTRACT: Chronic obstructive pulmonary disease (COPD) is an increasing health problem in people with HIV (PWH), and mechanisms of HIV COPD are poorly understood. Translocation of microbes or microbial products into the circulation as a result of increased mucosal permeability occurs in HIV, stimulates systemic inflammation, and has been linked to end-organ damage. Studies have largely focused on translocation of bacteria from the gut. We and others find that fungal translocation, defined by detection of 1,3-beta-D-glucan (BDG), occurs in PWH in the absence of invasive fungal infection. BDG is a pathogen-associated molecular pattern and fungal cell wall component that activates immune cells and triggers inflammation, and high systemic BDG levels correlate with circulating immune mediators in PWH and uninfected populations. Our preliminary data show that BDG is associated with worse lung function in HIV. In vitro, BDG increases lung epithelial and immune cell expression of inflammatory mediators, suggesting that BDG contributes directly to disease pathogenesis. While these data support a role of fungal translocation in HIV COPD, we do not know how BDG if circulating BDG is tied to epithelial disruption, how it relates to the host fungal microbiome, or how BDG leads impacts lung function. Here, we test the hypotheses that circulating BDG in HIV (1) originates from the lung fungal mycobiome in the setting of impaired lung permeability, (2) predicts worse respiratory symptoms and function, and (3) leads to impaired lung function via effects on circulating leukocytes. Using our established Pittsburgh HIV Lung cohort and in vitro lung modeling, we propose the following aims: Aim 1: To assess the relationship between gut and lung epithelial barrier integrity, the fungal mycobiome, and circulating BDG levels in PWH. We test the hypothesis that circulating BDG originates in the lung as well as the gut by assessing intestinal and lung permeability with functional assays and epithelial injury biomarkers and plasma BDG. We will also analyze fungal communities of the aerodigestive tract and circulating fungal DNA. Aim 2: To investigate if higher circulating BDG levels predict disease progression and systemic immune cell activation in HIV COPD. We will test the hypothesis that PWH with higher BDG levels have worse lung function and respiratory morbidity over time and that BDG is related to lung function and immune activation. Aim 3. To determine if BDG causes lung inflammation via dectin-1 in circulating immune cells from PWH. Based on our preliminary data, we hypothesize that the primary effect of BDG is from stimulation of inflammation in PBMCs by the dectin-1 receptor with increased magnitude of biological impact in the setting of HIV and will use combinations of BDG, conditioned media from HIV+ PBMCs, transwell insert culture models of well- differentiated human airway epithelial cells, and state-of-the-art Human Lung Small Airway-on-a-Chip. These studies ...