Role of oxidative stress in the suppression of immune responses in peripheral blood mononuclear cells exposed to combustible tobacco product preparations
Cigarette smoking is a major risk factor for several human diseases. Chronic inflammation, resulting from increased oxidative stress, has been suggested as a mechanism that contributes to the increased susceptibility of smokers to cancer and microbial infections. We have previously shown that whole smoke-conditioned medium (WS-CM) and total particulate matter (TPM) prepared from Kentucky 3R4F reference cigarettes potently suppressed agonist-stimulated cytokine secretion and target cell killing in peripheral blood mononuclear cells (PBMCs) under ex vivo conditions.
Here, we sought to investigate the role of oxidative stress from cigarette smoke exposure in the compromised immunity observed in smokers. Particularly, we investigated the mechanisms of WS-CM and TPM induced suppression of select cytokine secretions in Toll-like receptor (TLR) agonist-stimulated cells, and target cell killing by effector cells in PBMCs. Pre-treatment with N-acetyl cysteine (NAC), a precursor of reduced glutathione and an established antioxidant, protected against DNA damage and cytotoxicity (measured by γ-H2AX and 7-AAD staining, respectively) caused by exposure to WS-CM and TPM. Similarly, secretion of interferon-γ, tumor necrosis factor, interleukin (IL)-6 and IL-8 in response to TLR-4 stimulation was restored by NAC. Target cell killing, which is used as a functional measure of cytolytic cells in PBMCs, is suppressed by WS-CM. Pre-treatment with NAC restored the target cell killing in WS-CM treated PBMCs. This was accompanied by higher perforin levels in the effector cell populations. Collectively, these data suggest that reducing oxidative stress caused by cigarette smoke components restores select immune responses in this ex vivo model.