ANALYSIS OF MONOCYTE CHEMOATTRACTANT PROTEIN 1-MEDIATED LUNG INJURY USING RAT LUNG ORGAN-CULTURES

Using a rat lung organ culture system, we analyzed the role of monocyt e chemoattractant protein 1 (MCP 1) in leukocyte to lung adhesive inte ractions and monocyte-mediated lung injury. Quantitative leukocyte to lung adhesive interactions were examined using an adaptation of the Wo odruff-Stamper frozen section binding assay. Pretreatment of organ cul tures with recombinant human tumor necrosis factor (rhTNFalpha) result ed in a protein synthesis-dependent increase in the adhesiveness of lu ng tissue for peripheral blood monocytes. Adhesion of monocytes to lun g tissue was not increased above baseline after 7 hours but increased more than twofold by 24 hours and persisted through 48 hours. Binding of monocyte to lung tissue was further increased when recombinant rat MCP 1 was added to monocyte suspensions immediately before being layer ed onto lung sections derived from either TNFalpha-treated or untreate d organ cultures. Addition of antibody directed against rat CD11b/c re sulted in a moderate reduction in monocyte binding. TNF or lipopolysac charide-induced activation of mono-nuclear cells in the presence of [H -3]leucine-labeled organ cultures resulted in lung injury as assessed by radioisotope release. Mononuclear cell-mediated organ culture injur y could be partially inhibited with anti-rat MCP 1 antibody, anti-rat CD11b/c antibody, or antioxidants including catalase and deferoxamine. Anti-MCP 1 and anti-CD11b/c increased the absolute numbers of monocyt es that could be retrieved from monocyte-lung co-cultures while catala se and deferoxamine did not. In vitro studies revealed that isolated r at peripheral blood monocytes produce O2- in response to MCP 1. These data provide afunctional correlate for recent in vitro studies which s uggest that MCP 1 may mediate leukocyte adhesive processes by up-regul ating beta2 integrin expression on monocytes. This study provides evid ence that monocytes activated by MCP 1 can damage lung tissue through an oxidant-mediated mechanism Monocyte chemoattractant protein 1 may p articipate in the pathogenesis of monocyte-mediated lung injury by mod ulating inflammatory cell adhesion as well as through monocyte activat ion.