Selective Suppression of Neutrophil Accumulation in Ongoing Pulmonary Inflammation by Systemic Inhibition of p38 Mitogen-Activated Protein Kinase 1 Jerry A. Nick, 2 * § Scott K. Young,* Patrick G. Arndt,* § Jonathan G. Lieber, † Benjamin T. Suratt, § Katie R. Poch,* Natalie J. Avdi,* Ken C. Malcolm, † Christian Taube, † Peter M. Henson, †‡ and G. Scott Worthen* § The p38 mitogen-activated protein kinase (MAPK) signaling pathway regulates a wide range of inflammatory responses in many different cells. Inhibition of p38 MAPK before exposing a cell to stress stimuli has profound anti-inflammatory effects, but little is known about the effects of p38 MAPK inhibition on ongoing inflammatory responses. LPS-induced activation of p38 MAPK in human neutrophils was inhibited by poststimulation exposure to a p38 MAPK inhibitor (M39). Release of TNF-, macrophage- inflammatory protein (MIP)-2 (MIP-1), and IL-8 by LPS-stimulated neutrophils was also reduced by poststimulation p38 MAPK inhibition. In contrast, release of monocyte chemoattractant protein-1 was found to be p38 MAPK independent. Ongoing che- motaxis toward IL-8 was eliminated by p38 MAPK inhibition, although the rate of nondirectional movement was not reduced. A murine model of acute LPS-induced lung inflammation was used to study the effect of p38 MAPK inhibition in ongoing pulmonary inflammation. Initial pulmonary cell responses occur within 4 h of stimulation in this model, so M39 was administered 4 h or 12 h after exposure of the animals to aerosolized LPS to avoid inhibition of cytokine release. Quantities of TNF-, MIP-2, KC, or monocyte chemoattractant protein-1 recovered from bronchial alveolar lavage or serum were not changed. Recruitment of neu- trophils, but not other leukocytes, to the airspaces was significantly reduced. Together, these data demonstrate the selective reduction of LPS-induced neutrophil recruitment to the airspaces, independent of suppression of other inflammatory responses. These findings support the feasibility of p38 MAPK inhibition as a selective intervention to reduce neutrophilic inflammation. The Journal of Immunology, 2002, 169: 5260 –5269. R apid accumulation of neutrophils to a site of inflamma- tion is a defining early event of innate immunity. Neu- trophil recruitment to the airspaces is induced by cyto- kines, chemokines, and other inflammatory mediators released by resident alveolar macrophages and other cells of the lung. Neutro- phils are induced to leave the pulmonary vasculature, migrate through the lung interstitium, and ultimately accumulate in the airways through a complex series of events including sequential changes in cell size and stiffness, up-regulation of adhesion mol- ecules, cytoskeletal rearrangement, and chemotaxis (1– 4). A sec- ondary recruitment of monocytes and macrophages typically fol- lows the initial neutrophil influx, and the neutrophil itself may serve to amplify and perpetuate the recruitment of other leukocytes to the airspaces in certain disease states (5, 6). In a number of inflammatory lung diseases such as cystic fibrosis and the acute respiratory distress syndrome, neutrophil recruitment is prolonged and likely contributes to airway injury. Stress-induced responses of many cell types are regulated by signal transduction via the mitogen-activated protein kinase (MAPK) 3 superfamily (7). Like all mammalian cells, the neutro- phil contains at least three distinct families of MAPKs: the p42/44 extracellular signal-regulated kinase (ERK) MAPKs, c-Jun NH 2 - terminal kinases (JNKs), and p38 MAPKs (8 –10). In the setting of inflammation, cytokine release and other functional responses by pulmonary host defense cells are regulated to varying degrees by p38 MAPK. For example, inhibition of p38 MAPK blocks TNF- and IL-8 release by LPS-stimulated monocyte/macrophage (10 –12), IL-8 release by bronchial epithelial cells, and up-regula- tion of the ICAM-1 in endothelial cells when exposed to inflam- matory stimuli (13, 14). The response of neutrophils to these cy- tokines and other proinflammatory mediators is also regulated by p38 MAPK. In stimulated neutrophils, p38 MAPK regulates dis- tinctly different functions, including adhesion, activation of NF- B, synthesis of TNF- and IL-8, superoxide anion release, che- motaxis, and apoptosis (15–18). As a short-lived, terminally differentiated primary cell, the neu- trophil appears to use fewer of the available intracellular signal transduction mechanisms, relying on the p38 MAPK cascade to regulate functional responses to nearly every type of environmen- tal stress. For example, in monocytes or macrophage cell lines, LPS can activate p42/44 (ERK) MAPK and JNK as well as the p38 Departments of *Medicine and † Pediatrics, and ‡ Program in Cell Biology, National Jewish Medical and Research Center, Denver, CO 80206; and § Division of Pulmo- nary Science and Critical Care Medicine, University of Colorado School of Medicine, Denver, CO 80262 Received for publication December 7, 2001. Accepted for publication August 21, 2002. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. 1 This work was supported by Grants HL68743, HL03657, HL-40784, HL-34303, HL-09640, and GM-30324 from the National Institutes of Health. 2 Address correspondence and reprint requests to Dr. Jerry A. Nick, National Jewish Medical and Research Center, K613d, 1400 Jackson Street, Denver, CO 80206. E-mail address: nickj@njc.org 3 Abbreviations used in this paper: MAPK, mitogen-activated protein kinase; ERK, extracellular signal-regulated kinase; JNK, c-Jun NH 2 -terminal kinase; MIP, mac- rophage-inflammatory protein; MCP, monocyte chemoattractant protein; ATF, acti- vated transcription factor; BAL, bronchial alveolar lavage; M I , McCutcheon index; NDM, nondirectional movement; MPO, myeloperoxidase; MAPKAP, MAPK-acti- vated protein. The Journal of Immunology Copyright © 2002 by The American Association of Immunologists, Inc. 0022-1767/02/$02.00