Human serum and mucosal antibody responses to outer membrane protein G1b of Moraxella catarrhalis in chronic obstructive pulmonary disease.

Moraxella catarrhalis is an important human pathogen that causes otitis media, sinusitis, and lower respiratory tract infections in adults with chronic obstructive pulmonary disease. Outer membrane protein G1b is a approximately 29-kDa protein that has a high degree of homology among strains, contains surface-exposed epitopes, and is a potential vaccine candidate. The ompG1b gene was cloned, expressed in Escherichia coli, and purified. To assess the expression of outer membrane protein G1b during human infection, paired serum and sputum supernatants from patients with chronic obstructive pulmonary disease followed prospectively were studied by enzyme-linked immunosorbent assays with recombinant outer membrane protein G1b to detect antibodies made specifically during carriage of M. catarrhalis. Overall, 39% of patients developed either a serum IgG (28.6%) or a sputum supernatant IgA (19.2%) response to outer membrane protein G1b following 100 episodes of acquisition and clearance of M. catarrhalis. A sputum supernatant IgA response was more likely following exacerbations compared with asymptomatic colonizations, whereas a serum IgG response occurred at similar rates. Serum IgG antibodies following natural infection were directed toward surface-exposed epitopes of outer membrane protein G1b. Overall, these studies show that outer membrane protein G1b is expressed during infection of the human respiratory tract and that human antibodies bind to outer membrane protein G1b epitopes on the bacterial surface. These observations indicate that outer membrane protein G1b should be evaluated further as a vaccine antigen.