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Increased IgA Expression in Lung Lymphoid Follicles in Severe Chronic Obstructive Pulmonary Disease

Rationale: Accumulation of B cells and lymphoid follicles (LFs) has been described in chronic obstructive pulmonary disease (COPD) airways, but the functional status of lung B cells remains poorly known. Objectives: To characterize LFs for expression of IgA, the main mucosal antibody. Methods: The presence of B cells and LFs, including intrafollicular IgA expression, were determined in the lung from patients with COPD (n = 37) versus control subjects (n = 34) by immunohistochemistry. We also evaluated follicular IgA responses in the lungs from mice infected with Pseudomonas aeruginosa (PAO1) (n = 10 per group) and in smoking mice. Measurements and Main Results: Whereas in smokers B‐cell numbers slightly increased, robust increases in B‐cell and LF numbers (mainly in distal airways) were only observed in severe COPD. Most follicular B cells were IgM+ (70‐80%), but IgA+ (and not IgG+) B‐cell numbers were increased in LFs from severe COPD compared with control subjects (twofold, 44.7% vs. 25.2%), and this was significant in distal but not proximal airways. Follicular IgA response was also observed in PAO1‐infected mouse lungs, but not after smoke exposure. Moreover, follicular IgA expression associated with expression of IL‐21, which was very potent to activate immunoglobulin production in vitro. Conclusions: This study shows that IgA production occurs in peribronchiolar LFs from severe COPD, where IL‐21‐producing T cells are present, and presumably represents a feature of exacerbated mucosal adaptive immune responses against microbial and/or self‐antigens.