Leukocyte extravasation: an immunoregulatory role for alpha-L-fucosidase?

Fucosylated oligosaccharides and glycoconjugates have been implicated in several biological events, including the cell-cell adhesion processes that mediate inflammation. Alpha-L-fucosidase (ALF) is an exoglycosidase that is involved in the hydrolytic degradation of alpha-L-fucose from glycoconjugates. In this study, we investigated the potential role of ALF in regulation of leukocyte migration. Measurement of transendothelial migration in response to CCL5 demonstrated that pretreatment of monocytic cells with ALF reduced migration (p = 0.0004) to a greater extent than treatment of the endothelial monolayer (p = 0.0374). Treatment with ALF significantly reduced the adhesion of monocytic cells to immobilized P-selectin.Fc. A murine model of experimental autoimmune uveitis was then used to show that treatment of splenic cells with ALF produced an 8.6-fold decrease in rolling and a 3.2-fold decrease in cell migration across the retinal vasculature. Further in vitro studies demonstrated that treatment of monocytes with the chemokines CCL3 or CCL5 increased the level of mRNA encoding ALF; this was accompanied by the detection of significant increases in both the 51- and 56-kDa components of ALF by Western blotting. Treatment of monocytic cells with ALF for 2 h significantly reduced the cell surface expression of CD31, with a further decrease in expression observed after 5 h (p = 0.002). Thus, CD31 and fucosylated ligands of P-selectin seem to be the candidates through which ALF mediates its effect in vitro. These data identify a previously unrecognized immunoregulatory role for ALF in late stages of inflammation.

T cell extravasation: demonstration of synergy between activation of CXCR3 and the T cell receptor.

Endothelial cells present chemokines to T cells and can also stimulate the T cell antigen receptor by presentation of peptide-MHC antigen complexes. This study was designed to investigate the potential synergy between stimulation of the chemokine receptor CXCR3 and the human T cell receptor complex. Transendothelial T cell migration towards CXCL10 was modified by crosslinking CD3 immediately before addition to the endothelium. When resting endothelium was used, T cells which had been activated by crosslinking CD3 for only 1 min showed a significant reduction (p<0.0001) in migration when compared with untreated T cells. By contrast, endothelial cells which had been activated by stimulation with interferon-gamma and tumour necrosis factor-alpha supported a specific increase in the migration of activated T cells; this was most apparent after CD3 had been activated for 90 min (p<0.0001). The molecular basis for synergy between CXCR3 and the T cell receptor complex was investigated by measurement of fluorescence resonance energy transfer. This showed that CXCL10 induced a close (<10 nm) spatial association between CXCR3 and the CD3epsilon subunit on the cell-surface. These data demonstrate that stimulation of both CXCR3 and the T cell receptor has the potential to enhance specifically both the proliferation and extravasation of specific T cells during episodes of local inflammation.