Tumor necrosis factor-alpha -308 promoter gene polymorphism and increased tumor necrosis factor serum bioactivity in farmer's lung patients.

Hypersensitivity pneumonitis (HP) represents an immunologic reaction of the pulmonary parenchyma to an inhaled agent. Since tumor necrosis factor (TNF)-alpha is thought to be involved in the pathogenesis of HP, and polymorphisms in the TNF genes have been associated with variations in the production of TNF-alpha, we investigated the serum bioactivity and genotype of TNF in HP. TNF bioactivity was measured after hay dust challenge in eight patients with farmer's lung (Group A) and in 12 healthy, sensitized (antibody-positive) controls (Group B). Genotyping for the -308 TNF-alpha promoter polymorphism and the TNF-beta intron 1 gene polymorphism was performed in 20 patients with farmer's lung, 25 patients with pigeon breeder's lung, and 216 controls. TNF bioactivity increased in Group A at 4 to 10 h after hay dust challenge, but not in Group B (p < 0.05). The frequency for the TNFA2 allele, a genotype associated with high TNF-alpha production in vitro, was significantly higher in farmer's lung patients (frequency [f] = 0.43, p = 0.0012) than in controls (f = 0.19) or patients with pigeon breeder's lung (f = 0.16). Genotyping for TNF-beta revealed no significant abnormalities. Thus, increased production of TNF-alpha after hay contact, and a genetic predisposition to TNF-alpha production, are implicated in the pathogenesis of alveolitis in farmer's lung.