Interaction of Bacterial Pili and Leukocytes

Since Duguid and Guilles first described the ability of piliated bacteria to bind to leukocytes, much has been learned about the nature of this interaction. Mannose-sensitive (MS) pili bind to specific mannose-containing receptors on the leukocyte surface. While MS pili are responsible for attachment, the relative hydrophobicity of the bacterial surface determines whether the organism is internalized. Both binding and ingestion trigger the leukocyte to respond with degranulation and enhanced oxidative activity. The response to piliated bacteria, however, is delayed as compared to bacteria opsonized with serum, which may account for the reduced bactericidal activity associated with pili-mediated phagocytosis. A number of factors appear to influence the significance of pili-mediated phagocytosis in vivo. These include natural selective pressures in the host tissue, the ability of the organism to undergo pili phase transition and the presence of serum or other host opsonic factors. Antipili antibody does not enhance leukocyte killing of MS + Escherichia coli, but does stimulate leukocyte metabolic activity. Antipili antibody may, therefore, have an adverse effect on the infectious process by promoting the extracellular release of inflammatory material from the granulocyte.