Pro-inflammatory and oxidative responses to burn pit relevant desert particulate matter in macrophages: A role for TLR2 signaling

This is the authors' abstract. We don't add key points for this paper.

Particulate matter (PM) exposure is linked to many respiratory diseases such as asthma, yet the underlying mechanisms remain unclear. A large number of warfighters deployed to Afghanistan and Iraqi have developed deployment related respiratory disease. This study investigates the effects of burn pit-relevant desert PM from Afghanistan (APM) and comparative desert PM from China Lake, California (CPM) on oxidative stress and pro-inflammatory responses in macrophages. Using mouse monocyte cell line and primary bone marrow-derived macrophages (BMDMs) with or without Toll-like Receptor 2 (TLR2) deficiency, we assessed nitric oxide (NO . ), hydrogen peroxide (H 2 O 2 ), and cytokine production using biochemical assays, enzyme-linked immunosorbent assay (ELISA), pharmacological and genetic modulation, and bulk RNA sequencing. APM was more cytotoxic than CPM in monocytes. Both PMs increased H 2 O 2 levels, with acellular conditions generating higher H 2 O 2 levels, which was catalase-sensitive and attenuated by metal chelation. APM induced stronger NO . and cytokine C-X-C motif chemokine ligand 1 (CXCL1) responses than CPM, with NO . production attenuated by the nitric oxide synthase (NOS) inhibitor L-N G -nitroarginine methyl ester (LNAME), which also prevented cytotoxicity. TLR2 activation via agonist Pam3CSK4 enhanced NO . and CXCL1, while inhibition with antagonist C29 or TLR2 knockout partially suppressed APM-induced responses. Bulk RNA sequencing revealed that APM upregulated M1 pro-inflammatory polarization markers, many of which were significantly reduced in TLR2-deficient BMDMs. These findings demonstrate that APM exposure of monocytes/macrophages elicits stronger oxidative and pro-inflammatory responses than CPM, partially mediated through TLR2 signaling. This study provides mechanistic insight into deployment-related PM exposure and identifies potential therapeutic targets to mitigate inflammation in affected individuals. • APM is more cytotoxic and induced stronger NO . and CXCL1 responses than CPM • APM-induced NO . , was attenuated by NOS inhibition, which also reduced cytotoxicity • PMs elevated H 2 O 2 that was catalase-sensitive and was attenuated by metal chelation • TLR2 signaling mediates inflammatory responses to APM in macrophages • APM upregulates M1 polarization markers that was partially TLR2-dependent