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Infection and Immunity, October 2005, p. 6601-6607, Vol. 73, No. 10
0019-9567/05/$08.00+0     doi:10.1128/IAI.73.10.6601-6607.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Human Antibody Response to Outer Membrane Protein G1a, a Lipoprotein of Moraxella catarrhalis

Department of Microbiology and Immunology,¹ Department of Medicine, University at Buffalo, State University of New York, Buffalo, New York 14215,² Veterans Affairs Western New York Healthcare System, Medical Research 151, 3495 Bailey Ave., Buffalo, New York 14215,³ Department of Microbiology, Australian Bacterial Pathogenesis Program, Monash University, Victoria 3800, Australia⁴

Received 28 April 2005/ Returned for modification 31 May 2005/ Accepted 17 June 2005

Moraxella catarrhalis is an important cause of respiratory infections in adults with chronic obstructive pulmonary disease (COPD) and of otitis media in children. Outer membrane protein (OMP) G1a is an 29-kDa surface lipoprotein and is a potential vaccine candidate. The gene that encodes OMP G1a was expressed and purified using a novel plasmid vector. [³H]palmitic acid labeling demonstrated that both native and recombinant OMP G1a contain covalently bound palmitic acid. To assess the expression of OMP G1a during human infection, paired sera and sputum supernatants from adults with COPD followed prospectively were studied by enzyme-linked immunosorbent assays with recombinant lipidated OMP G1a to detect antibodies made specifically during carriage of M. catarrhalis. Overall, 23% of patients developed either a serum immunoglobulin G (IgG) response (9%) or sputum IgA response (21%) to OMP G1a, following 100 episodes of acquisition and clearance of M. catarrhalis. Patients developed antibody responses at similar rates following episodes of clinical exacerbation compared to asymptomatic colonization. Serum IgG antibodies following natural infection were directed predominantly at OMP G1a epitopes that are not exposed on the bacterial surface. These data show that OMP G1a is expressed during infection of the human respiratory tract and is a target of systemic and mucosal antibodies. These observations indicate that OMP G1a, a highly conserved surface protein, should be evaluated further as a vaccine candidate.

Editor: D. L. Burns

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