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Pulmonary macrophage phagocytosis of Pseudomonas aeruginosa is defective when this pathogen is opsonized with IgG antibodies isolated from serum samples from patients with cystic fibrosis (CF). To evaluate this defect further, IgG subclasses in the serum and lung fluids of patients with CF were quantitated. The pattern of IgG subclasses in serum specimens from patients with CF (n = 15) and in patients without CF but with chronic obstructive airway disease and recurrent P. aeruginosa infection (n = 4) was significantly altered from that found in normal subjects (n = 31). Immunoglobulin-G2 and IgG3 expressed as percentages of total IgG subclasses or in micrograms per milliliter of serum were significantly elevated in the serum specimens of these patients (p less than 0.05), and IgG1 was significantly decreased (p less than 0.01). It appears that the increase in IgG2 in the serum of patients with CF and those without CF but with chronic P. aeruginosa infection may be in response to chronic antigenic stimulation by P. aeruginosa lipopolysaccharide. Evidence presented to support this includes: (1) IgG2 is not increased in CF serum if a history of P. aeruginosa infection is absent, (2) IgG2 levels expressed as percentages of total IgG subclasses in CF lung fluids were positively correlated (r = 0.73) with the number of colony-forming units of P. aeruginosa present in CF sputum specimens, and (3) IgG antibodies specifically eluted from P. aeruginosa lipopolysaccharide ligands on affinity gels were largely restricted to IgG2. The opsonic index, ([IgG3] + [IgG1]) divided by ([IgG2] + [IgG4]), is inverted in CF lung fluids (0.73:1; normal, 2:1). Because pulmonary macrophages show surface receptors binding primarily with IgG3 and IgG1, it may be that such an alteration in IgG subclasses in the respiratory secretions of patients with CF further inhibits opsonin-mediated clearance of P. aeruginosa.

In the disease cystic fibrosis (CF), pulmonary infection with Pseudomonas aeruginosa is a common clinical complication that determines most morbidity and almost all excess mortality. We postulated that in this disease a defect in Pseudomonas-reactive IgG antibodies may contribute to chronic Pseudomonas infections. Bronchoalveolar lavages were performed upon 13 patients with CF, 7 patients with chronic bronchitis characterized by recurrent Pseudomonas infections, and 4 normal volunteers. The levels of various proteins important to host defenses and proteases were determined; enzyme inhibition studies were performed. CF respiratory immunoglobulin levels were significantly elevated when compared with both normals and patients with chronic bronchitis (P less than 0.05). Albumin and transferrin levels were decreased in the CF lung fluids. CF elastolytic activity was strikingly elevated (means = 6.02 micrograms/mg total protein) and the inhibitory profile suggested such activity resembled a serine-proteinase. Alpha-1-antitrypsin antigenic levels were not altered in CF respiratory fluids. There was a tendency for the lavage IgG to fall as elastase levels rose (r = -0.29). IgG opsonins for two Pseudomonas immunotypes were isolated with affinity chromatography for functional and immunochemical studies. Bacterial phagocytic rates in the presence of these Pseudomonas-reactive IgG opsonins derived from CF lavage fluid were depressed (0.3% uptake/unit time) when compared with similarly titered positive controls (uptake = 1.3%/unit time, P less than 0.001). Additionally, normal pulmonary macrophage intracellular killing of Pseudomonas was severely altered in the presence of opsonins derived from CF respiratory fluids. At some time points, less than 30% of the bacteria were killed. CF IgG opsonins contain a cleavage fragment (100,000 D, 5S sedimentation coefficient) with antigenic determinants similar to the Fab portion of IgG. The presence of such a fragment was inversely correlated with phagocytic functional activity. Intact IgG comprised as little as 18% of the CF lavage fluid specimens. Aliquots of intact human IgG, when mixed with the CF opsonins, augmented Pseudomonas uptake and improved intracellular killing. Conversely, peptide fragments of IgG opsonins, which are proteolytically derived in vitro, duplicated in our system the defect observed with opsonins derived from CF lung fluids; bacterial uptake was inversely related to the concentration of F(ab')2 and to a greater degree, to Fc present in the opsonic mixture. We concluded that IgG respiratory opsonins are fragmented, inhibiting phagocytosis and serving a permissive role in the chronic Pseudomonas pulmonary infection in the disease CF.

To study how fragmented IgG antibodies might arise within the respiratory secretions of individuals with cystic fibrosis (CF), we screened protease extracts from CF polymorphonuclear leukocytes and mucoid and nonmucoid transformants of Pseudomonas aeruginosa from patients with CF for IgG proteolytic activity. All strains of P. aeruginosa tested exhibited IgG proteolytic activity. Incubation for 7 hr at 37 C was required to demonstrate generation of free Fc gamma immunoreactivity. Further analysis of these cleavage products of CF IgG demonstrated generation of Fc gamma polypeptides with 4S sedimentation coefficients and F(ab')2 fragments with 5S coefficients. Bacterial IgG proteolytic activity was inhibited by EDTA and was associated with levels of bacterial elastase exceeding 5 micrograms/mg of total protein. Pseudomonas elastase was significantly more active on IgG1 and IgG3; IgG2 and IgG4 were more resistant. This bacterial exoproduct appears to digest IgG molecules into Fab gamma, F(ab')2 fragments, and a free Fc gamma piece with a molecular weight of 40,000.