Secretory IgA response against Pseudomonas aeruginosa in the upper airways and the link with chronic lung infection in cystic fibrosis

We assessed the diagnostic ability of an enzyme-linked immunosorbent assay test for measurement of specific secretory IgA (sIgA) in saliva to identify cystic fibrosis (CF) patients with Pseudomonas aeruginosa chronic lung infection and intermittent lung colonization. A total of 102 Brazilian CF patients and 53 healthy controls were included. Specific serum IgG response was used as a surrogate to distinguish CF patients according to their P. aeruginosa colonization/infection status. The rate of sIgA positivity was 87.1% in CF chronically infected patients (median value = 181.5 U/mL), 48.7% in intermittently colonized patients (median value = 45.8 U/mL) and 21.8% in free of infection patients ( median value = 22.1 U/mL). sIgA levels in saliva were significantly associated with serum P. aeruginosa IgG and microbiological culture results. The sensitivity, specificity, PPV and NPV for differentiation between presence and absence of chronic lung infection were 87%, 63%, 51% and 92%, respectively. Measurement of sIgA in saliva may be used for screening patients in risk of developing P. aeruginosa chronic lung infection in CF and possibly also for paranasal sinusitis, and, most importantly, to efficiently rule out chronic P. aeruginosa lung infection.