Pulmonary Immune Cell Landscape Altered by Exposure to HIV, Schistosoma and Their Combination

Local immune cell activation and vascular remodelling are characteristic pathogenic features of pulmonary arterial hypertension (PAH). HIV and schistosome infections have been individually associated with PAH. However, whether co-infection with these pathogens has a distinct impact on the development of pulmonary vascular disease remains poorly understood, partly due to the lack of experimental animal models. In a novel non-infectious model of HIV and Schistosoma pulmonary co-exposure based on lung embolisation of S. mansoni eggs in HIV-transgenic (HIV) mice, we previously reported exacerbated endothelial remodelling and dysfunction, along with increased pulmonary arterial pressure; which were associated with a unique profile of pro-inflammatory cytokines in the lung. In the present study, we used flow cytometric analysis of isolated lung leukocytes and immunofluorescence staining to characterise the pulmonary immune cell landscape associated with individual or combined exposure to HIV and schistosome. Compared with mice exposed to HIV (untreated HIV mice) or schistosome (egg-treated wild-type mice), co-exposed (egg-treated HIV mice) animals showed significantly increased numbers of interstitial and alveolar macrophages, patrolling-type monocytes, NKT and γδ T cells, and reduced CD8⁺ αβ T cells. Other lung immune cells, including inflammatory-type monocytes, eosinophils/neutrophils, dendritic cells, CD4⁺ αβ T cells, NK cells and B cells were not significantly affected in the co-exposure condition. Taken together, these results show for the first time that combined pulmonary exposure to HIV and Schistosoma, as it may occur in co-infected individuals, alters the local immune cell landscape in a manner distinct from that of individual exposure. Furthermore, these findings may contribute to a better understanding of the complex inflammatory processes involved in the pathogenesis of PAH, thereby supporting the development of therapies targeting pathogenic immune cells in pulmonary vascular disease associated with HIV and Schistosoma co-morbidity.