Dystroglycan is selectively cleaved at the parenchymal basement membrane at sites of leukocyte extravasation in experimental autoimmune encephalomyelitis

Role of the extracellular matrix in lymphocyte migration

“…Insert: β-Dystroglycan alone (asterisk vessel lumen). Bars 50 μm togenic CD4+ T cells cannot interact with these two laminin isoforms, even though they express the receptors capable of mediating such interactions (α6β1; Sixt et al 2001), suggesting that the extracellular milleu is an important factor in determining migratory mechanisms in encephalitogenic T cells (Agrawal et al 2006;Sixt et al 2001).…”

“…Disease symptoms are induced only upon leukocyte penetration of the parenchymal basement membrane and glia limitans and entry into CNS parenchyma. As the endothelial and parenchymal basement membranes are biochemically distinct (Agrawal et al 2006;Sixt et al 2001), this model further permits the investigation of leukocyte migration across two different basement membranes.…”

“…As several proteases, in particular MMPs, exist in an inactive form that requires in situ activation, mRNA and protein expression is not sufficient to identify sites of protease activity. The use of novel techniques that permit simultaneous in situ zymography for protease activity and immunofluorescence for the identification of cellular or extracellular markers has revealed that the majority of the protease activity associated with infiltrating leukocytes is gelatinase activity (MMP-2 and MMP-9), occurring focally subjacent to the parenchymal basement membrane at sites of leukocyte penetration of the CNS (Agrawal et al 2006). The involvement of the gelatinases in EAE has been substantiated by inhibitor studies (Gijbels et al 1994;Morini et al 2004), and current data suggest that infiltrating CD4+ encephalitogenic T lymphocytes are not the major source of gelatinases in vivo, but rather infiltrating macrophages and an additional CNS resident cell population (Agrawal et al 2006;Toft-Hansen et al 2006).…”

“…The use of novel techniques that permit simultaneous in situ zymography for protease activity and immunofluorescence for the identification of cellular or extracellular markers has revealed that the majority of the protease activity associated with infiltrating leukocytes is gelatinase activity (MMP-2 and MMP-9), occurring focally subjacent to the parenchymal basement membrane at sites of leukocyte penetration of the CNS (Agrawal et al 2006). The involvement of the gelatinases in EAE has been substantiated by inhibitor studies (Gijbels et al 1994;Morini et al 2004), and current data suggest that infiltrating CD4+ encephalitogenic T lymphocytes are not the major source of gelatinases in vivo, but rather infiltrating macrophages and an additional CNS resident cell population (Agrawal et al 2006;Toft-Hansen et al 2006). The reason that encephalitogenic T cells use different mechanisms to penetrate endothelial versus parenchymal basement membranes may be related to the basement membrane composition: parenchymal basement membrane is biochemically distinct from endothelial cell basement membrane, with the expression of laminins α1 and α2 rather than the endothelial cell laminins α4 and α5 (Fig.…”

“…Furthermore, the isoform composition of the four major basement membrane components varies with tissue type, and variations in their proportions or the predominant isoforms present might have major effects on both direct and indirect interactions within the network (for a review, see Hallmann et al 2005). The most physiologically relevant studies of the basement membrane contribution to leukocyte extravasation therefore utilize in vivo inflammatory models (Agrawal et al 2006;Engelhardt 1997;Sixt et al 2001;Yadav et al 2003) or intravital approaches (Kawakami et al 2005;Wang et al 2006), both of which have suggested an important role for the laminin family of basement membrane components.…”