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Infection and Immunity, May 2007, p. 2441-2450, Vol. 75, No. 5
0019-9567/07/$08.00+0     doi:10.1128/IAI.01635-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Physiological Osmotic Induction of Leptospira interrogans Adhesion: LigA and LigB Bind Extracellular Matrix Proteins and Fibrinogen

Division of Infectious Diseases, 111F, Veterans Affairs Greater Los Angeles Healthcare System, Los Angeles, California 90073,¹ Department of Medicine,² Department of Pathology and Laboratory Medicine, David Geffen School of Medicine at University of California—Los Angeles, Los Angeles, California 90095³

Received 11 October 2006/ Returned for modification 5 December 2006/ Accepted 2 February 2007

Transmission of leptospirosis occurs through contact of mucous membranes and abraded skin with freshwater contaminated by pathogenic Leptospira spp. Exposure to physiological osmolarity induces leptospires to express high levels of the Lig surface proteins containing imperfect immunoglobulin-like repeats that are shared or differ between LigA and LigB. We report that osmotic induction of Lig is accompanied by 1.6- to 2.5-fold increases in leptospiral adhesion to immobilized extracellular matrix and plasma proteins, including collagens I and IV, laminin, and especially fibronectin and fibrinogen. Recombinant LigA-unique and LigB-unique repeat proteins bind to these same host ligands. We found that the avidity of LigB in binding fibronectin is comparable to that of the Staphylococcus aureus FnBPA D repeats. Both LigA- and LigB-unique repeats interact with the amino-terminal fibrin- and gelatin-binding domains of fibronectin, which are also recognized by fibronectin-binding proteins mediating the adhesion of other microbial pathogens. In contrast, repeats common to both LigA and LigB do not bind these host proteins, and nonrepeat sequences in the carboxy-terminal domain of LigB show only weak interaction with fibronectin and fibrinogen. A functional role for the binding activity of LigA and LigB is suggested by the ability of the recombinants to inhibit leptospiral adhesion to fibronectin by 28% and 21%, respectively. The binding of LigA and LigB to multiple ligands present in different tissues suggests that these adhesins may be involved in the initial colonization and dissemination stages of leptospirosis. The characterization of the Lig adhesin function should aid the design of Lig-based vaccines and serodiagnostic tests.

Published ahead of print on 12 February 2007.

Editor: V. J. DiRita

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