Post-endotoxin exposure-induced lung inflammation and resolution consequences beneficially impacted by lung-delivered IL-10 therapy

Abstract

Although lung diseases typically result from long-term exposures, even a robust, one-time exposure can result in long-lasting consequences. Endotoxin is a ubiquitous environmental/occupational inflammatory agent often used to model airway inflammation. Using a murine model, the return to lung homeostasis following high dose inhalant lipopolysaccharide (LPS, 10–100 μg) exposure were delineated over 2 weeks. LPS-induced rapid weight loss, release of proinflammatory mediators, and inflammatory cell influx with prolonged persistence of activated macrophages CD11c+CD11b+ and recruited/transitioning CD11cintCD11b+ monocyte-macrophages out to 2 weeks. Next, lung-delivered recombinant (r) interleukin (IL)-10 was intratracheally administered for 3 doses initiated 5 h following LPS (10 μg) exposure for 2 days. IL-10 therapy reduced LPS-induced weight loss and increased blood glucose levels. Whereas there was no difference in LPS-induced bronchoalveolar lavage airway fluid cellular influx, total lung cell infiltrates were reduced (37%) with rIL-10 treatment. Post-LPS exposure treatment with rIL-10 strikingly reduced lavage fluid and lung homogenate levels of tumor necrosis factor-α (88% and 93% reduction, respectively), IL-6 (98% and 94% reduction), CXCL1 (66% and 75% reduction), and CXCL2 (47% and 67% reduction). LPS-induced recruited monocyte-macrophages (CD11cintCD11b+) were reduced (68%) with rIL-10. Correspondingly, LPS-induced lung tissue CCR2+ inflammatory monocyte-macrophage were reduced with rIL-10. There were also reductions in LPS-induced lung neutrophils, lymphocyte subpopulations, collagen content, and vimentin expression. These findings support the importance of studying resolution processes for the development of treatment after unintended environmental/occupational biohazard exposures. Short-term, lung-delivered rIL-10 favorably hastened inflammatory recovery processes following acute, high dose inhalant LPS exposure.

Targeting transitioning lung monocytes/macrophages as treatment strategies in lung disease related to environmental exposures

“…For experiments using heterozygous CCR2 +/RFP animals, male and female mice were utilized. For the CCR2 KO (and clodronate liposome studies), male mice were utilized, as male mice had increased in ammatory responses with less experimental variability following LPS exposure, consistent with prior studies (12,27). Mice were randomized, with AJN, AG, and animal facility staff aware of the randomization, whereas all other authors were blinded.…”

“…From cell-free lung tissue homogenates, levels of TNF-α, IL-6, murine neutrophil chemoattractant CXCL1, murine monocyte (and leukocyte) chemoattractants CCL2 and CCL7, and transforming growth factor (TGF)-β were quantitated by ELISA (R&D Systems, Minneapolis, MN) with minimal detectable difference (MDD) of 1.88, 1.6, 2.0, 0. T cells, CD19 + B cells, and NK cells were performed as previously reported (12,17,18) with associated RFP + gating per cell population (Supplemental Fig. 1 and Fig.…”

“…The VENTANA image viewer (version 3.1.4; Roche Diagnostics, Indianapolis, IN) was utilized to capture 10 images per lung section at 20x from scanned images. Collagen content in trichrome images was quanti ed as previously described (12,34) using Image J FIJI plugin (version: 2.9.0/1.53t U.S. National Institutes of Health, Bethesda, MD).…”

“…Lipopolysaccharide (LPS) or endotoxin is found in the outer membrane of gram-negative bacteria (10)(11)(12) and acts as a wellde ned component of many organic dusts and disease-causing environmental exposures. A role for gram-positive cell wall components such as peptidoglycans (PGN) in mediating lung disease following organic dust exposures has also been identi ed.…”

“…Although dust and bacterial component-induced lymphocytic lung aggregates were reduced in T and B cell depleted mice, many in ammatory consequences persisted. Thus, there is growing interest in the immunopathogenic role of distinct lung monocyte-macrophage subpopulations recruited and induced following environmental exposures (12,21,22). CC motif chemokine receptor 2 (CCR2) is a critical facilitator of monocyte recruitment and activation via interaction with its high-a nity ligand CCL2 (23,24).…”