The purpose of this study was to investigate the effects of chronically inhaled particulate matter <2.5 μm (PM_2.5) on inflammatory cell populations in the lung and systemic circulation. A prominent component of air pollution exposure is a systemic inflammatory response that may exaggerate chronic diseases such as atherosclerosis and insulin resistance. T cell response was measured in wild-type C57B/L6, Foxp3-green fluorescent protein (GFP) “knockin,” and chemokine receptor 3 knockout (CXCR3^−/−) mice following 24–28 wk of PM_2.5 or filtered air. Chronic PM_2.5 exposure resulted in increased CXCR3-expressing CD4⁺ and CD8⁺ T cells in the lungs, spleen, and blood with elevation in CD11c⁺ macrophages in the lung and oxidized derivatives of 1-palmitoyl-2-arachidonyl-sn-glycero-3-phosphorylcholine in wild-type mice. CXCR3 deficiency decreased T cells in the lung. GFP⁺ regulatory T cells increased with PM_2.5 exposure in the spleen and blood of Foxp3-GFP mice but were present at very low levels in the lung irrespective of PM_2.5 exposure. Mixed lymphocyte cultures using primary, PM_2.5-treated macrophages demonstrated enhanced T cell proliferation. Our experiments indicate that PM_2.5 potentiates a proinflammatory Th1 response involving increased homing of CXCR3⁺ T effector cells to the lung and modulation of systemic T cell populations.