Receptor Interacting Protein 2 (RIP2) Is Dispensable for OVA-Induced Airway Inflammation in Mice

Abstract

Purpose: Asthma is a pulmonary chronic inflammatory disease characterized by airway obstruction and hyperresponsiveness. Pattern recognition receptors are known to play a key role in the development of allergic diseases as well as host defenses against microbial infection. Receptor interacting protein 2 (RIP2), a serine/threonine kinase, is an adaptor molecule of NOD1 and NOD2, and genetic variation in this receptor is known to be associated with the severity of allergic asthma in children. In this study, we examined the role of RIP2 in the development of allergic airway inflammation in a mouse model.

Methods: Airway inflammation was induced in mice through intranasal administration of ovalbumin (OVA) after 2 intraperitoneal immunizations with OVA. Lung inflammation and mucus hypersecretion were examined histologically and total cell infiltration in bronchoalveolar (BAL) fluids was determined. Levels of the Th2-related cytokines, IL-5 and IL-13, in lung extracts were measured by ELISA. Serum antigen-specific IgE and IgG1 levels were also assessed.

Results: OVA-induced lung inflammation and mucus hypersecretion were not different between WT and RIP2-deficient mice. The IL-5 and IL-13 levels in the bronchoalveolar (BAL) fluids were also not impaired in RIP2-deficient mice compared to WT mice. Moreover, RIP2 deficiency did not affect serum OVA-specific IgG1 and IgE levels.

Conclusions: Our results suggest that RIP2 is not associated with the development of allergic airway inflammation.

Keywords: IgE; RIP2; Th2; airway inflammation; ovalbumin.

Fig. 1

OVA-induced airway inflammation in WT and RIP2-deficient mice. A schematic diagram of the experimental design (A). Mice were sensitized by i.p. administration of OVA mixed with adjuvant at days 0, 1, 7, and 8. On days 14, 15, 21, and 22, mice were challenged with OVA or PBS. Photographs of lung tissues were obtained from H&E-stained sections (B) and histopathological scores were determined semi-quantitatively by microscopic examination (C). Total cell numbers in the BAL fluids were counted (D) and a differential cell count was performed using Diff-Quick staining (E). Data are expressed as means±SD.

Fig. 2

Hyperplasia of goblet cells and mucus hypersecretion in the bronchus of lung tissue. Lung sections were stained with PAS and examined by light microscopy. Areas in the black boxes are shown at a higher magnification on the right of each picture (A). Numbers of PAS-positive cells in the airway epithelium were counted. In each airway studied, the length of the basement membrane (BM) was measured using image analysis software. The results are presented as mean numbers of PAS-positive cells per micrometer of BM (B). Data are expressed as means±SD.

Fig. 3

Cytokine production in the lung tissue of WT and RIP2-deficient mice. Lung extracts from the right lungs of sacrificed mice. IL-5 (A) and IL-13 (B) levels in lung extracts were measured by ELISA. Data are expressed as means±SD. Coefficients of variations (%) are shown in brackets.

Fig. 4

Levels of OVA-specific IgE and IgG1 in the serum. Serum was obtained from blood samples collected 48 h after the last OVA challenge. Serum OVA-specific IgE (A) and IgG1 (B) levels were measured by ELISA. Data are expressed as means±SD.