Cigarette Smoke Exposure Inhibits Contact Hypersensitivity via the Generation of Platelet-Activating Factor Agonists

Abstract

Previous studies have established that pro-oxidative stressors suppress host immunity due to their ability to generate oxidized lipids with PAF-receptor (PAF-R) agonist activity. Although exposure to the pro-oxidative stressor cigarette smoke (CS) is known to exert immunomodulatory effects, little is known regarding the role of platelet-activating factor (PAF) in these events. The current studies sought to determine the role of PAF-R signaling in CS-mediated immunomodulatory effects. We demonstrate that CS exposure induces the generation of a transient PAF-R agonistic activity in the blood of mice. CS exposure inhibits contact hypersensitivity in a PAF-R-dependent manner as PAF-R-deficient mice were resistant to these effects. Blocking PAF-R agonist production either by systemic antioxidants or treatment with serum PAF-acetyl hydrolase enzyme blocked both the CS-mediated generation of PAF-R-agonists and PAF-R dependent inhibition of CHS reactions, indicating a role for oxidized glycerophosphocholines with PAF-R agonistic activity in this process. In addition, cyclooxygenase-2 (COX-2) inhibition did not block PAF-R agonist production but prevented CS-induced inhibition of CHS. This suggests that COX-2 acts downstream of the PAF-R in mediating CS-induced systemic immunosuppression. Moreover, CS-exposure induced a significant increase in the expression of the regulatory T cell reporter gene in FoxP3EGFP mice but not in FoxP3EGFP mice on a PAF-R-deficient background. Finally, Treg depletion via anti-CD25 antibodies blocked CS-mediated inhibition of CHS, indicating the potential involvement of Tregs in CS-mediated systemic immunosuppression. These studies provide the first evidence that the pro-oxidative stressor CS can modulate cutaneous immunity via the generation of PAF-R agonists produced through lipid oxidation.

Chemotherapeutic Agents Subvert Tumor Immunity by Generating Agonists of Platelet-Activating Factor

“…In some experiments, antioxidants were preincubated for 60 min before addition of chemotherapeutic agents or DMSO (0.5%) vehicle. The incubations were quenched by addition of 2 ml of ice-cold methanol followed by methylene chloride, and lipids extracted as described (17,18,20). …”

“…Several groups have demonstrated suppression of host immunity in the presence of various pro-oxidative stressors through a mechanism involving platelet-activating factor (1-alkyl-2-acetyl-glycerophosphocholine; PAF). Pro-oxidative stressors including aromatic hydrocarbons found in jet fuel, cigarette smoke, and ultraviolet B radiation (UVB) (14–18) generate ROS that can act directly on glycerophosphocholines (GPC) to produce oxidized GPC (Ox-GPC) which are potent PAF-receptor (PAF-R) agonists (18–21). Structural studies using mass spectrometry have identified more than a dozen Ox-GPC, including native PAF itself (20–24).…”

“…In addition to the ability of pro-oxidative stressors (e.g., UVB) or exogenous PAF-R agonists to inhibit host immunity as measured by contact hypersensitivity (CHS) responses to either chemical antigens such as 2, 4-dinitrofluorobenzene (DNFB) or delayed type hypersensitivity responses to antigens such as Candida albicans (14–18,29), recent studies have indicated that systemic PAF-R activation can augment experimental tumor growth in a process involving the cytokine IL-10 and Tregs (30). PAF-R antagonists have also been demonstrated to protect against UVB-mediated photocarcinogenesis in mice (31).…”

Systemic Platelet-activating Factor Receptor Activation Augments Experimental Lung Tumor Growth and Metastasis

“…Murine B16F10 and human SK23mel melanoma cells were a kind gift from Dr. Christopher E. Touloukian (Department of Surgery, Indiana University School of Medicine [IUSM], Indianapolis, IN). PAF-R expressing B16-PAFR and human KBP cells were created and characterized by us previously 18–20,32. These cells were maintained in either DMEM or Roswell Park Memorial Institute medium (RPMI) media with above mentioned supplements.…”

“…Functional PAF-R in LLC1 cells was accessed by intracellular Ca 2+ mobilization assay as described previously 19,20. In brief, LLC1 tumor cells, grown at optimum condition, were loaded with the Ca 2+ - sensitive fura-2-AM dye (4 μM in Hanks’ balanced salt solution [HBSS]) at 37°C for 90 min.…”