Mucosal repair is a complex event that immediately follows acute injury induced by ischemia and noxious luminal contents such as bile. In the small intestine, villous contraction is the initial phase of repair and is initiated by myofibroblasts that reside immediately beneath the epithelial basement membrane. Subsequent events include crawling of healthy epithelium adjacent to the wound, referred to as restitution. This is a highly regulated event involving signaling via basement membrane integrins by molecules such as focal adhesion kinase and growth factors. Interestingly, however, ex vivo studies of mammalian small intestine have revealed the importance of closure of the interepithelial tight junctions and the paracellular space. The critical role of tight junction closure is underscored by the prominent contribution of the paracellular space to measures of barrier function such as transepithelial electrical resistance. Additional roles are played by subepithelial cell populations, including neutrophils, related to their role in innate immunity. The net result of reparative mechanisms is remarkably rapid closure of mucosal wounds in mammalian tissues to prevent the onset of sepsis.

Regulation of leukocyte integrin avidity is a crucial aspect of inf lammation and immunity. The actin cytoskeleton has an important role in the regulation of integrin function, but the cytoskeletal proteins involved are largely unknown. Because inf lammatory stimuli that activate integrin-mediated adhesion in human polymorphonuclear neutrophils (PMN) and monocytes cause phosphorylation of the actin-bundling protein L-plastin, we tested whether Lplastin phosphorylation was involved in integrin activation. L-plastin-derived peptides that included the phosphorylation site (Ser-5) rapidly induced leukocyte integrin-mediated adhesion when introduced into the cytosol of freshly isolated primary human PMN and monocytes. Substitution of Ala for Ser-5 abolished the ability of the peptide to induce adhesion. Peptide-induced adhesion was sensitive to pharmacologic inhibition of phosphoinositol 3-kinase and protein kinase C, but adhesion induced by a peptide containing a phosphoserine at position 5 was insensitive to inhibition. These data establish a novel role for L-plastin in the regulation of leukocyte adhesion and suggest that many signaling events implicated in integrin regulation act via induction of L-plastin phosphorylation.

Circulating polymorphonuclear neutrophils (PMN) are quiescent, nonadherent cells that rapidly activate at sites of inflammation, where they develop the capacity to perform a repertoire of functions that are essential for host defense. Induction of integrin-mediated adhesion, which requires an increase in integrin avidity, is critical for the development of these effector functions. Although a variety of stimuli can activate integrins in PMN, the signaling cascades involved are unclear. Phosphatidylinositol (PI) 3-kinase has been implicated in integrin activation in a variety of cells, including PMN. In this work, we have examined activation of the PMN integrin ␣ M ␤ 2 , assessing both adhesion and generation of the epitope recognized by the activation-specific antibody CBRM1/5. We have found that PI 3-kinase has a role in activation of ␣ M ␤ 2 by immune complexes, but we have found no role for it in ␣ M ␤ 2 activation by ligands for trimeric G protein-coupled receptors, including formylmethionylleucylphenylalanine (fMLP), interleukin-8, and C5a. Cytochalasin D inhibition suggests a role for the actin cytoskeleton in immune complex activation of ␣ M ␤ 2 , but cytochalasin has no effect on fMLP-induced activation. Similarly, immune complex activation of the Rac/Cdc42-dependent serine/threonine kinase Pak1 is blocked by PI 3-kinase inhibitors, but fMLP-induced activation is not. These results demonstrate that two signaling pathways exist in PMN for activation of ␣ M ␤ 2 . One, induced by Fc␥R ligation, is PI 3-kinase-dependent and requires the actin cytoskeleton. The second, initiated by G protein-linked receptors, is PI 3-kinase-independent and cytochalasin-insensitive. Pak1 may be in a final common pathway leading to activation of ␣ M ␤ 2 .Phagocytes are essential cells in host defense of metazoan organisms because they prevent the systemic spread of invading pathogens. Phagocytic cells such as monocytes and polymorphonuclear leukocytes (PMN) 1 circulate throughout tissues to be able to initiate a rapid response to injury and infection. At sites of inflammation and infection, these cells perform many functions, including ingestion and killing of invading organisms, generation of inflammatory mediators, and initiation of an immune response. The acquisition of these effector functions required for successful host defense is called phagocyte activation. Adhesion is required to develop the full effector phenotype in phagocytes and, indeed, in other leukocytes as well (reviewed in Refs. 1 and 2). We have used human PMN as a model cell to study how adhesion regulates this phenotypic change and the critical role of leukocyte integrins in this process. PMN express ␤ 1 , ␤ 2 , and ␤ 3 integrins, but integrins other than the ␤ 2 family (also known as LeuCAM or CD18 integrins) are present in low number. In particular, the CD18 integrin ␣ M ␤ 2 plays a central role in PMN activation at sites of inflammation (3-9). PMN integrins including ␣ M ␤ 2 bind poorly to their ligands unless the cells are exposed to inflammatory stimul...

Results suggest that ultrasonographic measurement of mural thickness and evaluation of the appearance of the right dorsal colon may be useful in the diagnosis of right dorsal colitis in horses.

The properties of azithromycin suggest that it may be an alternative to erythromycin for treatment of Rhodococcus equi pneumonia in foals. To investigate this possibility, the disposition of azithromycin in plasma, polymorphonuclear leukocytes (PMN), and alveolar cells was examined after a single administration in foals. Azithromycin suspension was administered orally (p.o.) at a dose of 10 mg/kg to five healthy 2-3-month-old foals. Two weeks later, azithromycin for injection was administered by intravenous (i.v.) infusion at a dose of 5 mg/kg to the same foals. Plasma samples were collected after p.o. and i.v. administration. Peripheral blood PMN and bronchoalveolar lavage fluid and alveolar cells were collected after p.o. administration. Azithromycin concentrations were determined by reverse-phase high-performance liquid chromatography (HPLC) with coulometric electrochemical detection. Azithromycin p.o. absorption was variable with a mean systemic availability of 39% (+/-20%). The plasma half-life was 16 and 18.3 h after i.v. and p.o. administration, respectively. Azithromycin had a very large volume of distribution (V(d)) of 11.6 L/kg [V(d(ss))] and 12.4 L/kg [V(d(area))]. The large V(d) can be attributed to high tissue and intracellular concentrations, exhibited by the high concentration of azithromycin in PMN and alveolar cells. The PMN half-life was 49.2 h. Dosage of 10 mg/kg of azithromycin p.o. once daily for foals with R. equi pneumonia is recommended for further study.