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 mitogen-activated protein kinase (MAPK) and can impact on downstream events of leukocyte rolling, including adhesion, and emigration. Using a novel chemotactic assay in vivo, we visualized slow release of chemokine from an agarose gel positioned 350 microm from a postcapillary venule, which induced directed migration (chemotaxis) of neutrophils. In this system, keratinocyte-derived cytokine induced phosphorylation of p38 MAPK, which phosphorylated a downstream protein (ATF-2). This latter event was blocked by the concentration of p38 inhibitors used in this study. Mice were treated with two different p38 inhibitors: SKF86002 and SB203580. Neither inhibitor affected rolling 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 the 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 < 0.05). In addition to emigration, both p38 inhibitors impaired the ability of emigrated cells to migrate through the tissue toward the chemotactic stimulus. In fact, the majority of emigrated leukocytes in p38 inhibitor-treated animals remained within 50 microm of the venule. Superfusion of the tissue with SKF86002 (0.7 mM) to impact only on emigrated and not vascular leukocytes resulted in no impairment in emigration, but in a significant reduction in chemotaxis away from the vessel wall. Again, the majority of emigrated leukocytes remained within 50 microm of the blood vessel. Our results suggest that p38 does not affect rolling or adhesion, but that it is involved in leukocyte emigration and chemotaxis through interstitium in response to keratinocyte-derived cytokine in vivo.