Mast Cell Activation as a Common Mechanism of Pulmonary Toxicity by Chemical Threat Agents

This research examines the role of mast cells in pulmonary toxicity caused by nitrogen mustard (NM), a surrogate for the chemical warfare agent sulfur mustard (SM). The study addresses a critical gap in understanding the mechanisms that drive inflammatory responses and lung injury following exposure to mustard agents. Recognizing that mast cells are one of the first innate immune cells present at mucosal lung surfaces and that SM can activate mast cells in skin, the investigators hypothesized that NM exposure promotes mast cell activation that contributes to acute and potentially long-term respiratory inflammation. To test this hypothesis, the study compared outcomes in wild-type C57BL/6J mice and mast cell-deficient B6.Cg-KitW-sh/HNihrJaeBsmJ (KitW-sh) mice following oropharyngeal aspiration of NM at a dose of 0.125 mg/kg with assessment at 72 hours.

Findings showed marked lung injury in C57BL/6J mice 72 hours after NM exposure, while injury was significantly abrogated in KitW-sh mice, implicating mast cells as central contributors to NM-mediated pulmonary damage. Both strains exhibited some degree of NM-induced damage, but C57BL/6J mice displayed higher inflammatory cell infiltration and elevated levels of prostaglandin D2 (PGD2) in bronchoalveolar lavage fluid (BALF) compared with the mast cell-deficient mice. Detailed BALF analysis revealed increased total cell counts and elevations in monocytes, eosinophils, and lymphocytes in C57BL/6J mice that were largely absent in KitW-sh mice after NM exposure. Histological analyses demonstrated immune cell infiltration and bronchiolar thickening in C57BL/6J lungs, accompanied by increased lactate dehydrogenase staining, consistent with tissue injury.

Complementing in vivo experiments, the researchers used murine bone marrow-derived mast cells to characterize NM-induced mast cell activation. While NM exposure did not cause classical mast cell degranulation in these assays, it did induce upregulation of bioactive mediators, specifically PGD2 and interleukin-6 (IL-6), indicating that mast cell activation in the context of NM may proceed through selective mediator production rather than overt degranulation. Elevated PGD2 and IL-6 provide mechanistic links between mast cell responses and the observed proinflammatory environment in the lung following NM exposure.

Collectively, the data support a prominent role for mast cells in the pathogenesis of NM-induced lung injury and identify mast cell-derived PGD2 and IL-6 as potential mediators of the acute inflammatory response. The study highlights mast cells as a possible mechanistic nexus through which inhaled mustard agents provoke pulmonary inflammation and tissue damage, offering a focused direction for future investigations of therapeutic interventions aimed at mitigating respiratory injury after exposure to SM or related chemical threats. These results are presented within a translational framework that considers both acute and potentially long-term consequences of mast cell-driven inflammation in the lung following chemical agent exposure.