TLR4 and inflammatory response: Using TLR2- and TLR4-deficient mice, we further demonstrated that PM<sub>2.5</sub>-induced increases in BAL cell counts, ROS, IL-6, and TNF-α were partially attenuated in TLR4 knockout mice, indicating a contributory but not exclusive role for TLR4 signaling in PM<sub>2.5</sub>-driven pulmonary inflammation.