Rationale: Hypersensitivity pneumonitis (HP) exhibits a diverse outcome. Patients with acute/subacute HP usually improve, whereas patients with chronic disease often progress to fibrosis. However, the mechanisms underlying this difference are unknown.

Objectives: To examine the T-cell profile from patients with subacute HP and chronic HP.

Methods: T cells were obtained by bronchoalveolar lavage from 25 patients with subacute HP, 30 patients with chronic HP, and 8 control subjects. T-cell phenotype and functional profile were evaluated by flow cytometry, cytometric bead array, and immunohistochemistry.

Measurements and main results: Patients with chronic HP showed higher CD4+:CD8+ ratio (median, 3.05; range, 0.3-15; subacute HP: median, 1.3; range, 0.1-10; control: median, 1.3; range, 0.7-2.0; P < 0.01), and a decrease of gammadeltaT cells (median, 2.0; range, 0.5-3.4; subacute HP: median, 10; range, 4.8-17; control: median, 15; range, 5-19; P < 0.01). Patients with chronic HP exhibited an increase in the terminally differentiated memory CD4+ and CD8+ T-cell subsets compared with patients with subacute HP (P < 0.05). However, memory cells from chronic HP showed lower IFN-gamma production and decreased cytotoxic activity by CD8+ T lymphocytes. Chronic HP displayed a Th2-like phenotype with increased CXCR4 expression (median, 6%; range, 1.7-36, vs. control subjects: median, 0.7%; range, 0.2-1.4; and subacute HP: median, 2.2%; range, 0.1-5.3; P < 0.01), and decreased CXCR3 expression (median, 4.3%; range, 1.4-25%, vs. subacute HP: median, 37%; range, 4.9-78%; P < 0.01). Likewise, supernatants from antigen-specific-stimulated cells from chronic HP produced higher levels of IL-4 (80 +/- 63 pg/ml vs. 25 +/- 7 pg/ml; P < 0.01), and lower levels of IFN-gamma (3,818 +/- 1671 pg/ml vs. 100 +/- 61 pg/ml; P < 0.01) compared with subacute HP.

Conclusions: Our findings indicate that patients with chronic HP lose effector T-cell function and exhibit skewing toward Th2 activity, which may be implicated in the fibrotic response that characterizes this clinical form.