CD44 Deficiency Leads to Enhanced Neutrophil Migration and Lung Injury in Escherichia coli Pneumonia in Mice

Abstract

CD44 is a major cell-surface receptor for hyaluronic acid (HA), a glycosaminoglycan component of extracellular matrix. HA-CD44 interactions have been implicated in leukocyte extravasation into an inflammatory site. This study examined the role of CD44 in acute inflammatory responses during pneumonias induced by Escherichia coli and Streptococcus pneumoniae using CD44-deficient mice. In E. coli-induced pneumonia, neutrophil accumulation in the lungs and edema formation was increased by 84% and 88%, respectively, in CD44-deficient mice compared to wild-type mice. In contrast, no difference was observed between these genotypes in S. pneumoniaeinduced pneumonia, and the HA content in the lungs decreased after instillation of S. pneumoniae, but not E. coli, in both genotypes. Studies to determine the mechanisms for this enhanced response showed that: 1) neutrophil apoptosis was not different between these two genotypes in either type of pneumonia; 2) CD44 deficiency resulted in enhanced mRNA expression of several inflammatory genes; and 3) CD44-deficient neutrophils migrated through Matrigel in response to chemoattractants faster and in greater numbers than wild-type neutrophils in vitro and this increase was in part dependent on HA content in the Matrigel. These data demonstrate that CD44 deficiency results in enhanced inflammation in E. coli but not S. pneumoniae-induced pneumonia, suggesting a previously unrecognized role for CD44 in limiting the inflammatory response to E. coli. Neutrophil accumulation at inflammatory sites is an important feature of acute inflammatory responses. During pulmonary inflammation, circulating neutrophils become sequestered within pulmonary capillaries, a process that does not require rolling. Neutrophils then migrate across the endothelium and through the pulmonary interstitium, which contains fibroblasts and extracellular matrix proteins such as collagens and proteoglycans.1-4 Finally, neutrophils migrate between alveolar epithelial cells, often between a type II and a type I pneumocyte, into the airspace. 1,5 CD44 is a type I transmembrane glycoprotein that is expressed by most cell types, including leukocytes, and is the major cell surface receptor for hyaluronan (HA). HA is a nonsulfated glycosaminoglycan component of the extracellular matrix and plays a major role in maintenance of tissue integrity.6 -8 CD44 has 10 different splice variants and neutrophils express the standard CD44 isoform, CD44s.9 CD44 may modulate immunological and inflammatory responses through at least two mechanisms. First, CD44 may play important roles in modulating leukocyte extravasation. Interaction between CD44 and HA is implicated in lymphocyte rolling and extravasation, and optimal binding of these two molecules is modulated by proinflammatory cytokines such as tumor necrosis factor-␣.10 -14 The role of CD44 in mediating neutrophil emigration during acute inflammatory responses is less well understood. Second, CD44 is capable of inducing signal transduction pathways and cell activation. Ligation of C...

CD44 Is Critically Involved in Infarct Healing by Regulating the Inflammatory and Fibrotic Response

“…In contrast, other investigations did not support an essential role for CD44 in mediating leukocyte infiltration in inflamed tissues, but suggested that CD44-hyaluronan interactions are important for suppression of inflammation and resolution of the inflammatory infiltrate. CD44 KO animals exhibited accentuated inflammation in a model of collagen-induced arthritis (28), were more susceptible to endotoxin-induced shock (29), and showed enhanced neutrophil migration and lung injury in murine bacterial pneumonia (30). In vitro experiments demonstrated that CD44 Ϫ/Ϫ neutrophils migrate faster through matrigel than WT neutrophils, suggesting that CD44 may slow neutrophil migration through extracellular matrix (30).…”

“…CD44 KO animals exhibited accentuated inflammation in a model of collagen-induced arthritis (28), were more susceptible to endotoxin-induced shock (29), and showed enhanced neutrophil migration and lung injury in murine bacterial pneumonia (30). In vitro experiments demonstrated that CD44 Ϫ/Ϫ neutrophils migrate faster through matrigel than WT neutrophils, suggesting that CD44 may slow neutrophil migration through extracellular matrix (30). These actions may be due to CD44-induced intracellular signaling events in leukocytes bound to hyaluronan or other ligands (30).…”

“…In vitro experiments demonstrated that CD44 Ϫ/Ϫ neutrophils migrate faster through matrigel than WT neutrophils, suggesting that CD44 may slow neutrophil migration through extracellular matrix (30). These actions may be due to CD44-induced intracellular signaling events in leukocytes bound to hyaluronan or other ligands (30). In addition, CD44 may prevent exaggerated inflammatory responses by promoting the expression of negative regulators of TLR-4 signaling (29).…”

CD44 is highly expressed on milk neutrophils in bovine mastitis and plays a role in their adhesion to matrix and mammary epithelium

“…In mice, CD44 expressed on hemopoietic cells is an important regulator of LPS-TLR signaling in macrophages, affecting pulmonary inflammatory response and PMN recruitment [9]. However, although intratracheal LPS [9] or intrapulmonary E. coli [18] challenge of CD44 −/− mice resulted in an exaggerated inflammatory response, none of this was found by us after an intramammary challenge (Gonen E. and Shpigel N.Y., unpublished results). Furthermore, although there is ample evidence for the possible role of CD44 in PMN extravasation, interstitial migration, and trans-epithelial migration, PMN recruitment was unaffected by CD44 deficiency in Figure 3.…”

Different susceptibilities of PECAM-deficient mouse strains to spontaneous idiopathic pneumonitis

“…In CD44-deficient mice, there was actually enhanced neutrophil migration to lung upon infection with E. coli (Wang et al, 2002). Blockade of CD18 integrins inhibits migration of neutrophils into the lung in response to experimental Pseudomonas aeruginosa and E. coli/lipopolysaccharide, as well as IgG immune-complex deposition, IL-1 and phorbol myristate acetate.…”