Cystic fibrosis pseudomonas opsonins. Inhibitory nature in an in vitro phagocytic assay

Pseudomonas aeruginosa infection plays a primary pathogenetic role in the chronic respiratory tract disease of cystic fibrosis (CF) patients. Despite pronounced humoral responses, reflected by high levels of antibodies against Pseudomonas in serum and in sputum, the antibodies do not eliminate this bacterium. In the present study we have used affinity chromatography with a lipopolysaccharide substituted immunoadsorbent gel to isolate high titers (mean(CF) = 1:256) of immunotype specific Pseudomonas IgG antibodies from the sera of nine CF subjects, and have evaluated the functional ability of these antibodies to promote phagocytosis and intracellular killing of P. aeruginosa in an in vitro human alveolar macrophage culture system. The phagocytic and intracellular bactericidal kinetics revealed that CF IgG antibodies function in an inhibitory fashion. Both the rate of phagocytosis (rate(CF) = 204 cpm/unit time) and absolute bacterial uptakes maximal at 120 min (uptake cf = 18 X 10^{3 14}C cpm) were inhibited compared with appropriate positive controls (hyperimmune serum, HIS; [rate(HIS) = 399; uptake(HIS) = 29 X 10³, P <0.005]). The ability of much CF-derived opsonins to potentiate microphage intracellular bactericidal processes was mildly impaired (bacterial survival(CF) = 15 X 10³ colony forming units (CFU)/min, survival(HIS) = 9 X 10³). Further characteriztion of this defect, assessed with functional studies of the Fab and Fc portions of the immunoglobulin molecule, revealed an impairment in the attachment of these specific anitbodies to the alveolar microphage membrane Fcγ receptors. Preliminary studies of the physical-chemical properties of these immunoglobulins were normal. The expression of this inhibitory activity in vivo may facilitate Pseudomonas colonization and the subsequent established infections in the respiratory tracts of CF subjects.