Adhesion of microbial pathogens to leukocyte integrins: Methods to study ligand mimicry

Abstract

This chapter reviews methods to determine if a bacterium adheres to a leukocyte integrin in an Arg-Gly-Asp (RGD)-dependent fashion and to identify the specific integrin and bacterial ligands involved and focuses on bacterial mimicry that allows integrin binding independent of RGD. To determine if bacteria ligate leukocyte β2 integrins, a downmodulation experiment can be used. The bacterial ligand for the integrin can be determined by testing the purified putative adhesin for the ability to downmodulate the leukocyte integrin in the assay described in the chapter. Another method to specify the bacterial ligand is to test the putative adhesin for the ability to compete with bacteria for the integrin. To confirm observations made in the downmodulation and competition assays, bacterial mutants that do not express the putative adhesin may be tested for a reduced ability to adhere to leukocytes spread on albumin-coated plastic surfaces in comparison to the wild type. The chapter describes different types of bacterial binding to leukocyte integrins, two of which focus on bacteria that bear the RGD sequence as the key motif recognized by the integrin and one of which focuses on bacterial lectins that bind carbohydrates decorating the integrin. A new type of integrin–bacteria interaction that is protein–protein in nature but RGD-independent is discussed in the chapter. This type of binding is characterized by bacterial mimicry of the natural ligands of the leukocyte integrin—for instance, the CD11b/CD18 ligands endotoxin, coagulation factor X, and C3bi. The chapter presents methods to study in vitro and in vivo the consequences of RGD and non-RGD binding for neutrophil adhesion and transendothelial migration in the host. The interaction of Bordetella pertussis with neutrophils, monocytes, and macrophages is used as an example. © 1995, Elsevier Inc. All rights reserved.