Antigenic specificity of the mucosal antibody response to Moraxella catarrhalis in chronic obstructive pulmonary disease

Abstract

Moraxella catarrhalis is an important human mucosal pathogen causing otitis media in children and lower respiratory tract infection in adults with chronic obstructive pulmonary disease (COPD). Little is known about the mucosal antibody response to M. catarrhalis in adults with COPD. In this study, 10 pairs of well-characterized sputum supernatant samples from adults with COPD who had acquired and subsequently cleared M. catarrhalis from their respiratory tracts were studied in detail in an effort to begin to elucidate potentially protective immune responses. Flow cytometry analysis was used to study the distribution of immunoglobulin isotypes in paired preacquisition and postclearance sputum samples. The results showed that immunoglobulin A (IgA) is the predominant M. catarrhalis-specific immunoglobulin isotype and that the sputum IgA contains a secretory component, indicating that it is locally produced at the mucosal site. Most patients made new sputum IgA responses to the adhesins UspA1 and Hag, along with the surface protein UspA2. A smaller proportion of patients made new sputum IgA responses to the iron-regulated proteins TbpB and CopB and to lipooligosaccharide. These results have important implications in understanding the mucosal immune response to M. catarrhalis in the setting of COPD and in elucidating the elements of a protective immune response.

FIG. 1.

Distribution of M. catarrhalis-specific immunoglobulin isotypes determined by flow cytometry using preacquisition and postclearance sputum supernatants with the homologous infecting strain. The x axis shows samples from 10 individual patients. The y axis indicates the percent increase of antibody in paired preacquisition and postclearance sputum samples determined by flow cytometry. Immunoglobulin isotypes are noted in the legend on the right. *, the percent increase of IgA in sample 4 was actually 1,425%.

FIG. 2.

Immunoblot assay of the purified outer membranes of M. catarrhalis strains (noted at the tops of lanes). Immunoblots were probed with purified IgA from homologous preacquisition sputum supernatants (lanes a) and postclearance sputum supernatants (lanes b) at identical concentrations. Antibodies were detected with peroxidase-conjugated rabbit anti-human IgA. Molecular masses are noted in kilodaltons on the right.

FIG. 3.

Immunoblot assays with purified lipooligosaccharide of M. catarrhalis strains (noted at the top). Immunoblots were probed with homologous preacquisition sputum supernatants (lanes a) and postclearance sputum supernatants (lanes b). Antibodies were detected with peroxidase-conjugated anti-human IgA. Molecular masses are noted in kilodaltons on the right. The arrow denotes the presence of IgA binding to lipooligosaccharide in the postclearance sputum sample.

FIG. 4.

Immunoblot assays with purified IgA from postclearance sputum supernatant samples corresponding to strain 7P94B1 (top panel) and strain 44P23B1 (bottom panel). Lanes contain purified outer membrane preparations of the following strains: the homologous strain (lane a), O35E (lane b), the UspA1 mutant (lance c), the UspA2 mutant (lane d), the UspA1 UspA2 double mutant (lane e), the CopB mutant (lane f), the TbpB mutant (lane g), the Hag mutant (lane h), and the UspA1 UspA2 Hag triple mutant (lane i). Antibodies were detected with peroxidase-conjugated anti-human IgA. Molecular mass markers are noted on the left in kilodaltons. Arrows denote the locations of UspA2, Hag, UspA1, and UspA2 monomers.