Serum IgA and IGg Subclasses During Treatment for Acute Respiratory Exacerbation in Cystic Fibrosis: Analysis of Patients Colonised with Mucoid or Non-Mucoid Strains of Pseudomonas Aeruginosa

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Abstract
Patients with cystic fibrosis (CF) have a high prevalence of Pseudomonas aeruginosa infection which causes chronic infection of the mucosal surfaces of the lung. This results in recurrent immune stimulation and hypergamma-globulinemia. The present study examines the levels of circulating Ig classes, IgG and IgA subclasses in 13 adult patients with CF during acute pulmonary infection and post-exacerbation. Total serum IgG levels were raised in the patients during infection and post-treatment when compared to the normal range (mean ± SEM: 17.21 ± 1.4 g/l vs 16.45 ± 1.5 g/l respectively; normal range 8 - 16 g/l). In contrast, total IgM (2.6 ± 0.26 vs 2.69 ± 2.74 g/l; normal range 0.6 - 2.8 g/l) and IgA levels (2.5 ± 0.52 vs 2.41 ± 0.48 g/l; normal range 0.5 - 4 g/l) remained unchanged when examined during all stages of the disease. Of the 13 patients studied, 69%, 39% and 31% had IgG, IgM and IgA levels respectively raised above the normal range values. The mean levels of individual IgG subclasses examined in this group of patients revealed values within the normal ranges, however IgG2 and IgG3 were increased in 31% and 46% of patients. Individual IgG3 levels fell in 77% (10/13) and IgG4 in 62% (8/13) of the patients post-exacerbation. With regard to IgA subclasses, significant reduction in the IgAl levels were observed post treatment (3687 ± 539 mg/l vs 2713 ± 498 mg/l, p<0.01). In contrast, IgA2 levels were increased from 279 ± 49 mg/l to 421 ± 69 mg/l, although statistical significance was not reached. Upon antibiotic treatment for infection, the findings in this study show that IgA1 which is susceptible to bacterial proteases is reduced with a concommitant increase in the protease resistant IgA2 subclass. Moreover, patients colonised with non-mucoid strains of P. aeroginosa had higher total IgA levels due to the raised IgAl subclass whereas they had lower IgG levels due to low IgG2 and IgG4 subclasses.

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