Nontypeable Haemophilus influenzae is an important respiratory pathogen, causing otitis media in children and lower respiratory tract infection in adults with chronic obstructive pulmonary disease (COPD). Immunoglobulin A1 (IgA1) protease is a well-described protein and potential virulence factor in this organism as well as other respiratory pathogens. IgA1 proteases cleave human IgA1, are involved in invasion, and display immunomodulatory effects. We have identified a second IgA1 protease gene, igaB, in H. influenzae that is present in addition to the previously described IgA1 protease gene, iga. Reverse transcriptase PCR and IgA1 protease assays indicated that the gene is transcribed, expressed, and enzymatically active in H. influenzae. The product of this gene is a type 2 IgA1 protease with homology to the iga gene of Neisseria species. Mutants that were deficient in iga, igaB, and both genes were constructed in H. influenzae strain 11P6H, a strain isolated from a patient with COPD who was experiencing an exacerbation. Analysis of these mutants indicated that igaB is the primary mediator of IgA1 protease activity in this strain. IgA1 protease activity assays on 20 clinical isolates indicated that the igaB gene is associated with increased levels of IgA1 protease activity. Approximately one-third of 297 strains of H. influenzae of diverse clinical and geographic origin contained igaB. Significant differences in the prevalence of igaB were observed among isolates from different sites of isolation (sputum > middle ear > nasopharynx). These data support the hypothesis that the newly discovered igaB gene is a potential virulence factor in nontypeable H. influenzae.Nontypeable Haemophilus influenzae, a gram-negative coccobacillus, is an important respiratory pathogen (36). This organism is the second most common cause of bacterial otitis media in children and the leading cause of recurrent otitis media (24,36). Nontypeable H. influenzae also plays an important role in the course and pathogenesis of chronic obstructive pulmonary disease (COPD). It is the most commonly isolated organism from the lower airways of adults with COPD and is the most common bacterial cause of exacerbations or periodic worsening of the disease (57). Nontypeable H. influenzae is also a contributing etiologic agent in sinusitis in children and adults as well as in adult pneumonia (36).A number of virulence factors have been identified in nontypeable H. influenzae, including (i) several adhesin molecules, which promote attachment to host structures; (ii) lipooligosaccharide, which promotes inflammation at the site of infection; and (iii) proteins involved in iron acquisition (49, 59, 60). Additionally, an enzyme which cleaves immunoglobulin A1 (IgA1) has been identified in H. influenzae (22,32). This capability is advantageous to this organism because IgA is the predominant mucosal immunoglobulin, and most of the IgA in the respiratory mucosa is of the IgA1 subclass (34).IgA1 proteases have been identified in several human mucosal pathogens, ...

Haemophilus influenzae is an important cause of otitis media in children and lower respiratory infection in adults with chronic obstructive pulmonary disease (COPD). Patients with COPD experience periodic exacerbations that are associated with acquisition of new bacterial strains. However, not every strain acquisition is associated with exacerbation. To test the hypothesis that genetic differences among strains account for differences in pathogenic potential, a microarray consisting of 4,992 random 1.5-to 3-kb genomic fragments of an exacerbation strain was constructed. Competitive hybridization was performed using six strains associated with exacerbation as well as five strains associated with asymptomatic colonization. Seven sequences that were absent in all five colonization strains and present in at least two exacerbation strains were identified. One such sequence was a previously unreported gene with high homology to the meningococcal immunoglobulin A (IgA) protease gene, which is distinct from the previously described H. influenzae IgA protease. To assess the distribution of the seven sequences among wellcharacterized strains of H. influenzae, 59 exacerbation strains and 73 asymptomatic colonization strains were screened by PCR for the presence of these sequences. The presence or absence of any single sequence was not significantly associated with exacerbations of COPD. However, logistic regression and subgroup analysis identified combinations of the presence and absence of genes that are associated with exacerbations. These results indicate that patterns of genes are associated with the ability of strains of H. influenzae to cause exacerbations of COPD, supporting the concept that differences in pathogenic potential are based in part on genomic differences among infecting strains, not merely host factors.