LEPTOSPIRA ICTEROHEMORRHAGIAE AND LEPTOSPIRE PEPTIDOLGYCANS INDUCE ENDOTHELIAL-CELL ADHESIVENESS FOR POLYMORPHONUCLEAR LEUKOCYTES

We have examined the effect of the virulent Leptospira interrogans str ain Teramo, serotype icterohemorrhagiae, on the adherence of human neu trophilic polymorphonuclear leukocytes (PMN) to cultured human umbilic al vein endothelial cells (HEC). Selective pretreatment of HEC with in tact or sonicated leptospires caused a dose- and time-dependent increa se of HEC-PMN adhesion (13.2% +/- 2.5% adherence to untreated HEC vers us 46.3% +/- 5.6% adherence to HEC pretreated for 4 h with 10(8) intac t leptospires per ml [mean +/- standard error of six experiments; P < 0.001]). In contrast, selective leptospire pretreatment of PMN or the addition of leptospires during the adherence assay did not alter HEC-P MN adherence, Leptospire induction of endothelial-cell adhesiveness oc curred without detectable HEC damage and was prevented by RNA and prot ein synthesis inhibitors and by monoclonal antibodies to the CD11/CD18 adhesion complex of neutrophils and to the endothelial-leukocyte adhe sion molecule 1 (ELAM-1) of endothelial cells. Similar results were ob tained with pretreatment of HEC with interleukin-1 or with the lipopol ysaccharide (LPS) of the gram-negative bacterium Escherichia coli. The possibility that contamination by the LPS of gram-negative bacteria c ould be involved in the induction of HEC adhesiveness was ruled out by the observation that the LPS inhibitor polymyxin B, which abolished t he proadhesive effect of E. coli LPS, was ineffective in inhibiting le ptospire- as well as interleukin-1-induced adherence. Similarly, lepto spire LPSs seemed to have no role in the increase of endothelial-cell adhesiveness, since pretreatment of HEC with a leptospire LPS extract (phenol-water method) or with a leptospire total lipid extract failed to induce the proadhesive phenotype for neutrophils. Instead, peptidog lycans extracted from our leptospires actively stimulated the endothel ial proadhesive activity for neutrophils (16.5% +/- 2.1% adherence to untreated HEC versus 51.2% +/- 2.9% adherence to HEC pretreated for 4 h with 1 mu g of peptidoglycan per ml; [mean +/- standard error of fou r experiments; P < 0.001]). This peptidoglycan-induced activity was in hibited by monoclonal antibodies to the CD11/CD18 adhesion complex and to ELAM-1 but not by polymyxin B. We conclude that peptidoglycans fro m pathogenic leptospires are among the molecules that can directly act ivate vascular endothelial cells to increase their adhesiveness for ne utrophilic granulocytes. These observations may contribute to a better understanding of the mechanisms whereby non-gramnegative bacteria mod ulate the local and systemic inflammatory reaction.