Effects of corticosteroids on osteopontin expression in a murine model of allergic asthma

Abstract

Background: Osteopontin (OPN) contributes to the development of T helper 1 (Th1)-mediated immunity and Th1-associated diseases. However, the role of OPN in bronchial asthma is unclear. Corticosteroids reduce airway inflammation, as reflected by the low eosinophil and T-cell counts, and the low level of cytokine expression. We investigated OPN production and the inhibitory effects of corticosteroids on OPN production in a murine model of allergic asthma.

Methods: BALB/c mice were sensitized by intraperitoneal injections of ovalbumin (OVA) with alum. Some mice received daily injections of dexamethasone (DEX) or phosphate-buffered saline for 1 week. All OVA-challenged mice were exposed to aerosolized 1% OVA for 30 min an hour after these injections. After the OVA challenge, the mice were killed, and bronchoalveolar lavage (BAL) fluid and lung tissue were examined.

Results: The levels of OPN protein in BAL fluid and OPN mRNA in lung tissue increased after OVA challenge. Most OPN-expressing cells were CD11c+ cells and some were T cells. DEX decreased the levels of OPN protein in the BAL fluid, and those of OPN mRNA and OPN protein in lung tissue.

Conclusions: OPN may play an important role in allergic bronchial asthma. Corticosteroids inhibit OPN production in mice with allergic asthma. The beneficial effect of corticosteroids in bronchial asthma is partly due to their inhibitory effects on OPN production.

Fig. 1.

OPN protein in BAL fluid and the effect of DEX on the OPN protein. The OPN protein levels in BAL fluid were significantly higher at 24 h after antigen challenge in the OVA-challenged mice than in the control mice. DEX significantly decreased the OPN protein levels in BAL fluid at 24 h after OVA challenge. ∗∗ OVA compared with control (p < 0.01). + DEX compared with OVA (p < 0.05).

Fig. 2.

OPN mRNA in the lungs and the effect of DEX on OPN mRNA. OPN mRNA expression in the lungs was significantly higher at 24 h after antigen challenge in the OVA-challenged mice than in the control mice. DEX significantly reduced OPN mRNA expression in the lungs. ∗∗ OVA compared with control (p < 0.01). + DEX compared with OVA (p < 0.05).

Fig. 3.

Immunohistochemical staining for OPN in lung tissues and the effect of DEX on OPN expression. In the control mice, only the bronchial epithelial cells were strongly positive for OPN (a). In contrast, in the OVA-challenged mice, OPN staining was predominately observed in the infiltrating cells, and to a lesser extent, in the bronchial epithelial cells 24 h after OVA challenge (b). Immunohistochemical staining for OPN was significantly reduced in the DEX-treated mice (c). a Control mice; b OVA mice; c DEX mice. Most OPN-expressing cells that stained positively were mainly CD11c cells in mice (d–f, j). In contrast, a few OPN-expressing cells belonged to the T-cell population (g–i, k). d OPN (red); e CD11c (green), and f double-positive cells (yellow). g OPN (red); h CD4 (green), and I, double-positive cells (yellow). j The numbers of CD11c-, OPN- and double-positive cells were counted. k The numbers of CD4-, OPN- and double-positive cells were counted.

Fig. 3.

Immunohistochemical staining for OPN in lung tissues and the effect of DEX on OPN expression. In the control mice, only the bronchial epithelial cells were strongly positive for OPN (a). In contrast, in the OVA-challenged mice, OPN staining was predominately observed in the infiltrating cells, and to a lesser extent, in the bronchial epithelial cells 24 h after OVA challenge (b). Immunohistochemical staining for OPN was significantly reduced in the DEX-treated mice (c). a Control mice; b OVA mice; c DEX mice. Most OPN-expressing cells that stained positively were mainly CD11c cells in mice (d–f, j). In contrast, a few OPN-expressing cells belonged to the T-cell population (g–i, k). d OPN (red); e CD11c (green), and f double-positive cells (yellow). g OPN (red); h CD4 (green), and I, double-positive cells (yellow). j The numbers of CD11c-, OPN- and double-positive cells were counted. k The numbers of CD4-, OPN- and double-positive cells were counted.

Fig. 3.

Immunohistochemical staining for OPN in lung tissues and the effect of DEX on OPN expression. In the control mice, only the bronchial epithelial cells were strongly positive for OPN (a). In contrast, in the OVA-challenged mice, OPN staining was predominately observed in the infiltrating cells, and to a lesser extent, in the bronchial epithelial cells 24 h after OVA challenge (b). Immunohistochemical staining for OPN was significantly reduced in the DEX-treated mice (c). a Control mice; b OVA mice; c DEX mice. Most OPN-expressing cells that stained positively were mainly CD11c cells in mice (d–f, j). In contrast, a few OPN-expressing cells belonged to the T-cell population (g–i, k). d OPN (red); e CD11c (green), and f double-positive cells (yellow). g OPN (red); h CD4 (green), and I, double-positive cells (yellow). j The numbers of CD11c-, OPN- and double-positive cells were counted. k The numbers of CD4-, OPN- and double-positive cells were counted.

Fig. 3.

Immunohistochemical staining for OPN in lung tissues and the effect of DEX on OPN expression. In the control mice, only the bronchial epithelial cells were strongly positive for OPN (a). In contrast, in the OVA-challenged mice, OPN staining was predominately observed in the infiltrating cells, and to a lesser extent, in the bronchial epithelial cells 24 h after OVA challenge (b). Immunohistochemical staining for OPN was significantly reduced in the DEX-treated mice (c). a Control mice; b OVA mice; c DEX mice. Most OPN-expressing cells that stained positively were mainly CD11c cells in mice (d–f, j). In contrast, a few OPN-expressing cells belonged to the T-cell population (g–i, k). d OPN (red); e CD11c (green), and f double-positive cells (yellow). g OPN (red); h CD4 (green), and I, double-positive cells (yellow). j The numbers of CD11c-, OPN- and double-positive cells were counted. k The numbers of CD4-, OPN- and double-positive cells were counted.