Pneumonia, a microbial infection involving the terminal airways and alveoli of the lung, is an important disease in the elderly, chronically ill and immunocompromised individuals. Considerable portion of the community- acquired and nosocomial pneumonia is caused by S. pneumoniae, H. influenzae, P. aeruginosa, K. pneumoniae and Enterobacter species. These organisms colonize the oropharynx prior to initiation of infection. MG1 (mucin derived from submandibular-sublingual saliva) which has the potential to selectively interact with a variety of bacteria by virtue of the presence of hundreds of oligosaccharides (receptors) may promote colonization in oropharynx. Aspiration of oropharyngeal secretions is thought to deliver pathogens colonizing in the oropharyngeal area to the lower airways. TBM (mucin derived from tracheobronchial secretions) may bind the aspirated bacteria and under normal circumstances these are cleared from the lung by ciliary action. However, disruption of the normal defense mechanisms may lead to colonization and infection of the lung. The long range goal of our studies is to understand the structure-function relationships of mucins in health and disease. The results of this application will answer the following: (1) the range of bacterial species which interact with TBM and MG1 and differences between colonized and infected bacterial strains in these interactions and (2) the structural domains involved in mucin (TBM and MG1)-bacterial interactions. More precisely, the specific aims of this application are to: (1) examine binding of 125 I-TBM and 125 I-MG1 to fresh isolates of Streptococcus pneumoniae, Haemophilus influenzae, Pseudomonas aeruginosa, Klebsiella pneumoniae and Enterobacter species obtained from patients with documented respiratory infection. We will also determine the selectivity and specificity of bacterial interaction by measuring the saturability, inhibitability, and reversibility of binding by 125 I-TBM and 125 I-MG1; and (2) compare binding of intact 125 I-TBM with deglycosylated 125 I-TBM, 125 I-TBM subunits and 125 I-delipidated TBM to selected strains of each bacterial species to determine the structural domains involved in bacterial interaction. If carbohydrate moieties are involved in bacterial binding, the identification of oligosaccharide receptors will be determined by employing purified and structurally characterized TBM oligosaccharides as inhibitors in binding assays.