## Doctoral Dissertations

Spring 1994

Dissertation

Microbiology

#### Degree Name

Doctor of Philosophy

Salmonella species are responsible for wide spread disease in both humans, and animals and macrophages (MO play a central role in host defenses against disease. Recent evidence has shown that MO bear surface receptors involved in direct microbial recognition. Using the mouse model and a virulent strain of S. typhimurium, we have attempted to determine the means by which peritoneal MO recognize this pathogen in the absence of serum factors. Bacterial adherence was monitored by direct microscopic visualization and by flow cytometry. Two strains of S. typhimurium strains 1826 and ATCC 14028 were used in this model. Adherence was much lower for strain 1826. Homologous wildtype lipopolysaccharide and, to lesser extent, Re glycolipid and the core sugar 2-keto-deoxyoctonate (KDO) effectively blocked bacterial binding. Two-deoxyglucose, known to inhibit phagocytosis via complement receptors (CR) or Fc receptors, and neutrophil elastase, which specifically cleaves CR1, each reduced binding. Monoclonal antibodies directed against the $\alpha$ and $\beta$ chains of CR3 also reduced binding. Residual bacterial binding activity remained even when both CR1 and CR3 were blocked. We suggest that the initial recognition is a multifactorial process involving ligands on the bacterial LPS and both CR1 and CR3 plus other as yet unidentified MO structures. The role of other receptors on MO was also examined. Antibody to C1q receptor enhanced binding of Salmonella to MO while antibodies to the Mac-2 and Mac-3 receptors had no effect. Using electrophoresis and Western blot techniques, we were able to isolate two MO membrane-proteins each with molecular weight of 16 and 13 kilodaltons. The proteins were identified by labeled bacteria cells. Similarly, we have identified S. typhimurium outer membrane protein that binds to macrophage. The protein has a molecular mass of 44 kilodaltons and is expressed under anaerobic conditions.