A novel pathway of rapid TLR-triggered activation of integrin-dependent leukocyte adhesion that requires Rap1 GTPase.
Bottom Line: Consistently, in vivo administration of the TLR2-ligand Pam3CSK4 increased integrin-dependent slow rolling and adhesion to endothelium within minutes, as identified by intravital microscopy in the cremaster model.TLR2 and TLR5 ligation increased β2-integrin affinity, as assessed by the detection of activation-dependent neoepitopes.This novel direct pathway linking initial pathogen recognition by TLRs to rapid β2-integrin activation may critically regulate acute leukocyte infiltration to sites of pathogen invasion.
Affiliation: Department of Clinical Pathobiochemistry, Technische Universität Dresden, 01309 Dresden, Germany Institute of Physiology, Technische Universität Dresden, 01309 Dresden, Germany email@example.com.Show MeSH
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Mentions: The rapid activation of leukocyte adhesion in vitro by TLR2 and TLR5 and in vivo by TLR2 ligation implied alterations in β2-integrin affinity rather than changes in their expression upon TLR2 and TLR5 ligation. To this end, we stimulated THP-1 myelomonocytes acutely (20 min) with TLR2 (HKLM) or TLR5 (flagellin) ligands, used TLR9 (ODN2006) ligand as a negative control, and assessed β2-integrin conformational status by flow cytometry using KIM127 and mAb24 antibodies, which recognize the intermediate- and high-affinity conformations on β2-integrins (Stanley et al., 2008; Kuwano et al., 2010). Acute TLR2 and TLR5 activation increased the expression of the KIM127- and mAb24-recognized neoepitopes on β2-integrins (Figure 3, A and B) without affecting β2-integrin expression. In contrast, TLR9 stimulation had no effect on the conformational status of β2-integrins (Figure 3, A and B). Additional experiments demonstrated that the activation of the conformational status of β2-integrins by TLR2 stimulation can be detected as early as 1 min upon treatment with the ligand (Supplemental Figure S2A). Thus TLR2 and TLR5 ligation can rapidly induce the intermediate- and high-affinity conformation of β2-integrins.
Affiliation: Department of Clinical Pathobiochemistry, Technische Universität Dresden, 01309 Dresden, Germany Institute of Physiology, Technische Universität Dresden, 01309 Dresden, Germany firstname.lastname@example.org.