(438) Investigating the role of Galectin-3 in a model of lung granuloma formation

Introduction/Rationale:

Introduction: Granulomas are structured clusters of macrophages and lymphocytes that form in tissues in response to persistent antigens and, in some diseases, without an identifiable cause. Granulomatous inflammation is central to the pathogenesis of certain infections, for example, those caused by mycobacteria. Mechanisms that drive granuloma formation, and whether they represent an adaptive or maladaptive response, remain poorly defined.

Methods:

Methods: We used mice deficient in Tsc2 gene expression in myeloid lineage cells (Tsc2ffLys2Cre+). An inoculum of 5x105 of the mycobacterium Bacille Calmette-Guérin (BCG) was administered intranasally and lung flow cytometry, histology, immunofluorescence and single cell RNA sequencing were performed.

Results:

Results: Following BCG challenge, we observed histologic evidence of progressive granuloma formation in the lungs, mediastinal lymph nodes, spleen, skin, and heart tissues over 11 weeks in Cre-positive mice, but not Cre-negative littermates. The granulomas were composed of large tissue macrophages, some forming multinucleated giant cells, surrounded by lymphocytes. Lung single cell transcriptional profiling identified an atypical histiocyte population in Cre-positive animals. We used these data to develop a flow cytometry gating strategy to identify this histiocyte population, using Galectin-3 as a key marker. Using Immunofluorescence, we observed the presence of Galectin-3 on the cell surface. The atypical histiocytes exhibited cell surface Galectin-3 expression and increased mitochondrial superoxide production. Targeting the carbohydrate-binding domain of galectin-3 with the synthetic small molecule inhibitor, TD139 (olitigaltin), resulted in lower numbers of these atypical histiocytes in the lungs.

Conclusion:

Conclusion: Histiocytes play a critical role in granuloma formation and maintenance. Galectin-3 can serve as a marker for histiocytes and may be a promising target for therapies aimed at treating granulomatous diseases.