Siglec-F is a sialic acid-binding Ig superfamily receptor that is highly expressed on eosinophils. We have investigated whether administration of an anti-Siglec-F Ab to OVA-challenged wild-type mice would reduce levels of eosinophilic inflammation and levels of airway remodeling. Mice sensitized to OVA and challenged repetitively with OVA for 1 mo who were administered an anti-Siglec-F Ab had significantly reduced levels of peribronchial eosinophilic inflammation and significantly reduced levels of subepithelial fibrosis as assessed by either trichrome staining or lung collagen levels. The anti-Siglec-F Ab reduced the number of bone marrow, blood, and tissue eosinophils, suggesting that the anti-Siglec-F Ab was reducing the production of eosinophils. Administration of a F(ab′)2 fragment of an anti-Siglec-F Ab also significantly reduced levels of eosinophilic inflammation in the lung and blood. FACS analysis demonstrated increased numbers of apoptotic cells (annexin V+/CCR3+ bronchoalveolar lavage and bone marrow cells) in anti-Siglec-F Ab-treated mice challenged with OVA. The anti-Siglec-F Ab significantly reduced the number of peribronchial major basic protein+/TGF-β+ cells, suggesting that reduced levels of eosinophil-derived TGF-β in anti-Siglec-F Ab-treated mice contributed to reduced levels of peribronchial fibrosis. Administration of the anti-Siglec-F Ab modestly reduced levels of periodic acid-Schiff-positive mucus cells and the thickness of the smooth muscle layer. Overall, these studies suggest that administration of an anti-Siglec-F Ab can significantly reduce levels of allergen-induced eosinophilic airway inflammation and features of airway remodeling, in particular subepithelial fibrosis, by reducing the production of eosinophils and increasing the number of apoptotic eosinophils in lung and bone marrow.

Siglec-F is a sialic acid binding immunoglobulin-superfamily receptor that is highly expressed on eosinophils. We have used a mouse model of oral egg ovalbumin (OVA)-induced eosinophilic inflammation of the gastrointestinal mucosa associated with diarrhea and weight loss to determine whether administering an anti-Siglec-F antibody would reduce levels of intestinal mucosal eosinophilic inflammation. Mice administered the anti-Siglec-F antibody had significantly lower levels of intestinal eosinophilic inflammation, and this was associated with reduced intestinal permeability changes, normalization of intestinal villous crypt height, and restoration of weight gain. The reduced numbers of intestinal eosinophils in anti-Siglec-F antibody treated mice was associated with significantly reduced numbers of bone marrow and peripheral blood eosinophils, but was not associated with significant changes in the numbers of proliferating or apoptotic jejunal eosinophils. In addition, the anti-Siglec-F Ab reduced Th2 cytokines and IgE levels. Overall, these studies demonstrate that administration of an anti-Siglec-F antibody significantly reduces levels of eosinophilic inflammation in the intestinal mucosa and that this was associated with reduced intestinal permeability changes, normalization of intestinal villous crypt height, and restoration of weight gain.

BackgroundIn this study we examined the role of Siglec-F, a receptor highly expressed on eosinophils, in contributing to mucus expression, airway remodeling, and Siglec-F ligand expression utilizing Siglec-F deficient mice exposed to chronic allergen challenge.MethodsWild type (WT) and Siglec-F deficient mice were sensitized and challenged chronically with OVA for one month. Levels of airway inflammation (eosinophils), Siglec-F ligand expresion and remodeling (mucus, fibrosis, smooth muscle thickness, extracellular matrix protein deposition) were assessed in lung sections by image analysis and immunohistology. Airway hyperreactivity to methacholine was assessed in intubated and ventilated mice.ResultsSiglec-F deficient mice challenged with OVA for one month had significantly increased numbers of BAL and peribronchial eosinophils compared to WT mice which was associated with a significant increase in mucus expression as assessed by the number of periodic acid Schiff positive airway epithelial cells. In addition, OVA challenged Siglec-F deficient mice had significantly increased levels of peribronchial fibrosis (total lung collagen, area of peribronchial trichrome staining), as well as increased numbers of peribronchial TGF-β1+ cells, and increased levels of expression of the extracellular matrix protein fibronectin compared to OVA challenged WT mice. Lung sections immunostained with a Siglec-Fc to detect Siglec-F ligand expression demonstrated higher levels of expression of the Siglec-F ligand in the peribronchial region in OVA challenged Siglec-F deficient mice compared to WT mice. WT and Siglec-F deficient mice challenged intranasally with IL-4 or IL-13 had significantly increased levels of airway epithelial Siglec-F ligand expression, whereas this was not observed in WT or Siglec-F deficient mice challenged with TNF-α. There was a significant increase in the thickness of the peribronchial smooth muscle layer in OVA challenged Siglec-F deficient mice, but this was not associated with significant increased airway hyperreactivity compared to WT mice.ConclusionsOverall, this study demonstrates an important role for Siglec-F in modulating levels of chronic eosinophilic airway inflammation, peribronchial fibrosis, thickness of the smooth muscle layer, mucus expression, fibronectin, and levels of peribronchial Siglec-F ligands suggesting that Siglec-F may normally function to limit levels of chronic eosinophilic inflammation and remodeling. In addition, IL-4 and IL-13 are important regulators of Siglec-F ligand expression by airway epithelium.