Oxidative stress caused by excessive reactive oxygen species production is implicated in influenza A virus-induced lung disease. Glutathione peroxidase (GPx)-1 is an antioxidant enzyme that may protect lungs from such damage. The objective of this study was to determine if GPx-1 protects the lung against influenza A virus-induced lung inflammation in vivo. Male wild-type (WT) or GPx-1(-/-) mice were inoculated with HKx31 (H3N2, 1 × 10(4) plaque-forming units), and bronchoalveolar lavage fluid (BALF)/lung compartments were analyzed on Days 3 and 7 after infection for inflammatory marker expression, histology, and viral titer. WT mice infected with HKx31 had significantly more BALF total cells, macrophages, neutrophils, and lymphocytes at Days 3 and 7 compared with naive WT animals (n = 5-8; P < 0.05). However, infected GPx-1(-/-) mice had significantly more BALF inflammation, which included more total cells, macrophages, and neutrophils, compared with WT mice, and this was abolished by treatment with the GPx mimetic ebselen. BALF inflammation persisted in GPx-1(-/-) mice on Day 10 after infection, and GPx-1(-/-) mice had significantly more influenza-specific CD8(+) T cells in spleen compared with WT mice (n = 3-4; P < 0.05). Infected GPx-1(-/-) mice had greater peribronchial and parenchymal inflammation than WT mice, and viral titer was significantly reduced in GPx-1(-/-) mice at Day 3 (n = 5; P < 0.05). Gene expression analysis revealed that infected GPx-1(-/-) mice had higher whole lung TNF-α, macrophage inflammatory protein (MIP)-1α, MIP-2, KC, and matrix metalloproteinase (MMP)-12 mRNA compared with infected WT mice. GPx-1(-/-) mice had more MIP-2 protein in BALF at Day 3 and more active MMP-9 protease in BALF at Days 3 and 7 than WT mice. These data indicate that GPx-1 reduces influenza A virus-induced lung inflammation.