Specific IgA against Pseudomonas aeruginosa in severe COPD.

BACKGROUND: The bronchial mucosa is protected by a specialized immune system focused on the prevention of colonization and infection by potentially pathogenic microorganisms (PPMs). Immunoglobulin A (IgA) is the principal antibody involved in this mechanism. A defective immune barrier may facilitate the recurrent presence of PPMs in COPD.

PURPOSE: The aim of this study was to determine IgA-mediated bronchial specific immune responses against Pseudomonas aeruginosa in stable patients with severe disease.

METHODS: COPD patients with good-quality sputum samples obtained during stability were included and classified according to the presence or absence of chronic bronchial colonization by P. aeruginosa . Levels of specific IgA for P. aeruginosa in sputum were determined by ELISA and expressed as ratios, using the pooled level of 10 healthy subjects as reference (optical density450 patient/control).

RESULTS: Thirty-six stable COPD patients were included, 15 of whom had chronic colonization by P. aeruginosa . Levels of specific IgA against P. aeruginosa in stable non-colonized patients were lower than those in healthy subjects (IgA ratio: median =0.15 [interquartile range {IQR} 0.05-0.36]). Colonized patients had higher levels, (1.56 [IQR 0.59-2.79]) ( p <0.001, Mann-Whitney U test), with figures equivalent but not exceeding the reference value.

CONCLUSION: IgA-based immune response against P. aeruginosa was low in severe COPD patients. Levels of specific IgA against this microorganism were higher in colonized patients, but did not attain clear-cut levels above the reference. An impaired local response against P. aeruginosa may favor chronic colonization and recurrent infections in severe COPD.