IgA1 (immunoglobulin A1), a predominant immunoglobulin, is at the first defense line against microbial pathogens infection and invasion, to neutralize pathogenic antigens. Some bacterial pathogens, such as Neisseria meningitidis and Haemophilus influenzae, however, secrete site-specific IgA1 proteases to counteract with the human defense system. The protease is capable of cleaving at the hinge region of immunoglobulin A1 to destroy the structure and function of human IgA1, impairing the role of the immunoglobulin from the host defense. The protease has therefore been implicated as a putative virulence factor that contributes to bacterial colonization, but bacterial isolates from patients with invasive diseases contain both positive and negative IgA1 proteases. To clarify the role of IgA1 protease in bacterial infection, this project is designed to reveal the molecular mechanism of the protease in bacterial infection and colonization. To do this, iga genes encoding non-typable H. influenzae type 1, type 3 and Neisseria meningitidis type 3 IgA1 proteases were isolated, sequenced and then expressed in IgA1 protease-negative E. coli BL21 (DE3). The recombinant proteases have been purified to homogeneity using ion exchange chromatography. Comparison of the deduced amino acid sequences from non-typable H. influenzae IgA1 proteases with other published H. influenzae IgA1 protease revealed a high degree of homology. Sequence analysis indicates that both type 1 and type 3 non-typable H. influenzae IgA1 proteases lack £\-protein in comparison with the iga from N. meningitidis. The role of IgA1 protease in relation to deposition and invasion has also been evaluated in human lung carcinoma cell (A549) model. The results suggest that the IgA1 protease plays a role in the adherence of H. influenzae on epithelial cell surface though the best effectiveness varies upon different pathogenic bacterial strains at different concentrations.

Some pathogenic bacteria including Haemophilus influenzae and Neisseria meningitides produce a protease called IgA1 protease to impair a major antibody, immunoglobulin A1 (IgA1), on human mucosal surfaces. The iga mRNA is initially translated into a precursor containing four distinct domains: a 31-amino acids signal peptide which leads the precursor to the periplasmic space, an 105-kDa protease domain which cleaves host IgA1 molecule, a £]-domain responsible for autotransportation of the protease domain, and a short linker between the protease and the £]-domains. The autotransporter £]-domain can be further divided into three subdomains in Neisseria protease: an extracellular linking region £\-protein and a membrane-embedded £]-core, between which there is a distinguished sequence called surface region. The hydrolytic function of the protease and the transporter role of £]-core had been studied extensively, but the £\-protein and the surface regions were less defined, or had their role characterized. Thus this study is designed to reveal the possible pathogenic functions of the £\-protein and the surface region in bacterial adherence to human cell surfaces. To complete this project, recombinant £\-protein and the surface region were expressed in IgA1 protease-negative E. coli strain (UT5600) respectively and purified to homogeneity. These recombinant proteins were used in cellular assays for bacterial adhesion on human lung cancer cell (A549). Four different invasive strains of pathogenic bacteria (IgA1 protease-positive or negative), were recruited in adherence assays to determine the effect of the purified £\-protein and the surface region on bacterial adherence to A549 cells. Results showed that the both £\-protein and the surface region played a role in bacterial adherence in a species-dependent manner.

Yes / Background. The roles of diffusely-adherent Escherichia coli (DAEC) and enteroaggregative E. coli (EAEC) in disease are not well understood, in part because of the limitations of diagnostic tests for each of these categories of diarrhoea-causing E. coli. A HEp-2 adherence assay is the Gold Standard for detecting both EAEC and DAEC but DNA probes with limited sensitivity are also employed. Results. We demonstrate that the daaC probe, conventionally used to detect DAEC, cross-reacts with a subset of strains belonging to the EAEC category. The cross hybridization is due to 84% identity, at the nucleotide level, between the daaC locus and the aggregative adherence fimbriae II cluster gene, aafC, present in some EAEC strains. Because aaf-positive EAEC show a better association with diarrhoea than other EAEC, this specific cross-hybridization may have contributed to an over-estimation of the association of daaC with disease in some studies. We have developed a discriminatory PCR-RFLP protocol to delineate EAEC strains detected by the daaC probe in molecular epidemiological studies. Conclusions. A PCR-RFLP protocol described herein can be used to identify aaf-positive EAEC and daaC-positive DAEC and to delineate these two types of diarrhoeagenic E. coli, which both react with the daaC probe. This should help to improve current understanding and future investigations of DAEC and EAEC epidemiology.