Our results show clearly that SCTE significantly modulated the pulmonary environment of Th1- (TNF-α) and Th2-type cytokines (IL-4, IL-13, and IL-33) and chemokines (eotaxin) in BALF, and inhibited iNOS expression and MMP-9 activity in the mouse lung tissue compared with the effects in OVA-induced mice. SCTE decreased the total and OVA-specific IgE level in plasma. In lung histopathological studies using H&E and PAS staining, SCTE inhibited inflammatory cell infiltration and mucus hypersecretion compared with the effects in OVA-challenged mice. SCTE also reduced IL-4 and IL-13 expression in Con-A-stimulated splenocytes.
Th2-type cytokines such as IL-4, IL-5, and IL-13 play important roles in the development of allergic asthmatic responses in humans
. SCTE treatment reduced the number of eosinophils in BALF and in the lung tissue surrounding the airways, and decreased the extent of goblet cell hyperplasia compared with untreated mice. However, there was little change in the numbers of other leukocytes such as neutrophils, lymphocytes, and macrophages. It is possible that the reduction in eosinophil numbers observed in our study reflects a decrease in IL-5-dependent eosinophil expansion. IL-5 plays an important role in the differentiation, maturation, and survival of eosinophils, which lead to an increased number of these cells in the airways subsequent to activation. A previous study has shown that eosinophilic inflammation does not develop in the absence of IL-5 or its signaling in the airways of OVA-sensitized/challenged mice
We found that SCTE reduced the production of IL-4, IL-5, and IL-13. IL-4 promotes the differentiation and proliferation of Th2-type T cells, and the switching of B cells to produce IgG1 and IgE. Blocking of IL-4 by monoclonal antibodies decreases IgE level and airway eosinophilia in allergic mice
. Therefore, suppression of IL-4 may also contribute to decreasing lung eosinophilia. Increased immunoreactive IL-33 level has a variety of effects on inflammatory cells. IL-33 is present in the peripheral blood
 and in BALF of asthmatic patients whose bronchial epithelium produces this cytokine at high levels
. IL-33 drives production of proinflammatory and Th2 cytokines by mast cells and Th2 lymphocytes
[25, 26], induces chemotaxis of Th2 cells
, promotes eosinophil and basophil adhesion, and increases eosinophil survival and basophil migration
. In the present study, IL-33 reduction by SCTE may help decrease lung and BALF eosinophil numbers. Th2 cytokines, especially IL-13, are central mediators of asthma, and IL-13 potently induces goblet cell metaplasia by human airway epithelial cells
. Therefore, in the present study, the decrease of goblet hyperplasia may reflect less IL-13 production compared with OVA-induced mice.
TNF-α is also an important chemoattractant for the recruitment of eosinophils into the lungs
 and is a potent modulator of the immune and inflammatory responses. Inflammatory cells contribute to the generation of Th2 cytokines (IL-4, IL-5, and IL-13), chemokines (eotaxin and RANTES), and TNF-α, whose levels increase in the asthmatic lung
. In our experiments, SCTE treatment reduced the levels of IL-4, IL-5, IL-13, TNF-α, and eotaxin; these findings are consistent with the change in inflammatory cell count in BALF. To identify the possible protective mechanism underlying the activity of SCTE in airway inflammation, we used gelatin zymography to evaluate the activity of MMP-9 and Western blotting to evaluate the expression of MMP-9 protein in lung tissue. We were interested in the relationship between MMP-9 expression and infiltration of inflammatory cells in lungs of the OVA-challenged mice. SCTE-treated OVA-induced mice showed reduced activity and protein expression of MMP-9 in lung tissue compared with control OVA-challenged mice. These results are consistent with the observed changes in cytokines. The dose-dependent changes are also consistent with those shown in an in vivo experiment in rats
Excessive NO may recruit eosinophils into the airway and shift the balance toward Th2 cells, thus exacerbating airway inflammation
. iNOS produces high amounts of NO. The present results from our OVA-induced asthma model showing decreased production of iNOS in lung tissues, increased inflammatory cytokine levels, and recruitment of eosinophils to the lung airways are consistent with the study by Nathan. In our experiments, SCTE significantly reduced goblet cell hyperplasia and mucus production in the OVA-induced murine asthmatic animals. Eosinophils infiltrating into the airway also increase mucus secretion of epithelial goblet cells
. These results suggest that mucus hypersecretion is attenuated by the ability of SCTE to limit cytokine production and eosinophilia, and that SCTE can inhibit the development of the allergic status in the OVA-induced asthma model.