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.