Abstract Rationale Prior Mycobacterium tuberculosis (Mtb) exposure may leave a lasting immune imprint in the distal airway, however the cellular and functional consequences are unknown. We examined how blood-based IGRA status relates to distal airway composition and early innate immune responses to Mtb; among individuals with historic tuberculosis-exposure residing in the Twin Cities area. Methods We enrolled 13 healthy non-smoking adults who have lived in tuberculosis (TB) endemic regions from more than 10 years. Our study group included 7 IGRA1 and 6 IGRA+ participants. We performed bronchioalveolar lavage to obtain distal airway cells, which were incubated with antibiotics for 4 hours, washed, and rested overnight. Cells were then infected with a luminescent or fluorescent strain of Mtb H37Rv (LUX or mCherry) and incubated for 6 hours before removal of extracellular bacteria. Bacterial growth was quantified over 5 days using luminescence as a surrogate for bacterial growth. Cytokine concentrations and cellular composition were assessed 24 hour post-infection by multiplex assay and flow cytometry. Results Alveolar macrophages were significantly more abundant in IGRA+ samples than in IGRA1 samples (88.1 % vs 50.3 % of live cells, p = 0.001). IGRA1 compared to IGRA+ samples contained higher proportions of lymphocytes and NK cells (10.4 % vs 2.6 %), neutrophils (9.8 % vs 4.0 %), monocytes (1.53% vs 1.1%) and dendritic cells (0.86 % vs 0.09 %). After Mtb infection, the proportion of alveolar macrophages in IGRA+ samples decreased to 70.9 % while lymphocytes and NK cells modestly increased to 3%, monocytes to 4.1% and neutrophils to 2.9%. In contrast, IGRA1 samples showed a rise in alveolar macrophages from 50.3% vs 57% and stable levels of other leukocytes, indicating that TB exposure drives distinct cellular compositional shifts following infection.Cytokine profiling showed strong induction of IL-1β and IFN-γ after infection in both groups, with a trend toward higher IL-8 and IL-1β secretion in IGRA1 cells. Despite these immune differences, bacterial uptake and growth over five days were similar between IGRA+ and IGRA1 samples. Conclusions Prior Mtb exposure described by IGRA status shapes the pulmonary immune cell landscape by expanding the alveolar macrophage pool and altering its cytokine response to infection. These findings suggest that IGRA status influences local lung immune composition, which in turn may shape early host-pathogen interactions and susceptibility to respiratory infections. This abstract is funded by: Early career research award from the University of Minnesota
Patino et al. (Fri,) studied this question.