Role of p38 mitogen-activated protein kinase in chemokine-induced emigration and chemotaxis in vivo

It has been proposed that L-selectin engagement with ligand activates p38 m itogen-activated protein kinase (MAPK) and can impact on downstream events of leukocyte rolling, including adhesion, and emigration. Using a novel che motactic assay in vivo, we visualized slow release of chemokine from an aga rose gel positioned 350 mum from a postcapillary venule, which induced dire cted migration (chemotaxis) of neutrophils. In this system, keratinocyte-de rived cytokine induced phosphorylation of p38 MAPK, which phosphorylated a downstream protein (ATF-2). This latter event was blocked by the concentrat ion of p38 inhibitors used in this study. Mice were treated with two differ ent p38 inhibitors: SKF86002 and SB203580. Neither inhibitor affected rolli ng or adhesion in microvessels. Intravenous treatment with SFK86002 (5, 10, and 20 mg/kg) 30 min before the inflammatory stimulus inhibited the total number of emigrated cells at a dose of 20 mg/kg (62%, p < 0.05), despite th e presence of many adherent cells within the vessels. A similar inhibition was observed with 20 mg/kg of a second p38 inhibitor SB203580 (67%, p < 0.0 5). In addition to emigration, both p38 inhibitors impaired the ability of emigrated cells to migrate through the tissue toward the chemotactic stimul us'. In fact, the majority of emigrated leukocytes in p38 inhibitor-treated animals remained within 50 mum of the venule. Superfusion of the tissue wi th SKF86002 (0.7 mM) to impact only on emigrated and not vascular leukocyte s resulted in no impairment in emigration, but in a significant reduction i n chemotaxis away from the vessel wall. Again, the majority of emigrated le ukocytes remained within 50 mum of the blood vessel. Our results suggest th at p38 does not affect rolling or adhesion, but that it is involved in leuk ocyte emigration and chemotaxis through interstitium in response to keratin ocyte-derived cytokine in vivo.