Heme Oxygenase-1 Attenuates Ovalbumin-Induced Airway Inflammation by Up-Regulation of Foxp3 T-Regulatory Cells, Interleukin-10, and Membrane-Bound Transforming Growth Factor- (cid:1) 1

Cumulative evidence suggests the up-regulation of interleukin (IL)-10 and T-regulatory (Treg) cells is implicated in anti-inflammatory effect of heme oxygen-ase-1 (HO-1). Thus, we postulated that induction of HO-1 could augment IL-10 and transforming growth factor (TGF)- (cid:1) production and foxp3 (cid:2) CD4 (cid:2) CD25 (cid:2) Treg cell function, thereby leading to attenuation of airway inflammation. In this study, CD4 (cid:2) CD25 (cid:2) Treg cells isolated from mouse spleen were either transfected with a HO-1 expression vector (pcDNA3HO-1) or treated with a HO-1 inducer (hemin). Up-regulation of HO-1 enhanced foxp3 expression and IL-10 secretion in the Treg cells in vitro . Next, BALB/c, C57/ B6.129, and IL-10-deficient B6.129P2- Il 10 tm1Cgn /J mice were challenged by ovalbumin to induce airway inflammation. Consistent with in vitro findings, hemin treatment resulted in induction of HO-1 and foxp3 and production of IL-10 and membrane-bound TGF- This was alleviated by hemin compared to OVA and SnPP treatment ( (cid:1) P (cid:8) 0.01), whereas SnPP inhibited the effect of hemin. B: OVA challenge significantly induced eosin- ophil infiltration in the lung ( # P (cid:8) 0.001). This was alleviated by hemin compared to OVA and SnPP treatment ( (cid:1) P (cid:8) 0.01), conversely SnPP inhib- ited the effect of hemin. These data are representative of three separate experiments. cell function. Thus, our data indicate that IL-10 and membrane-bound TGF- (cid:1) 1 play an important role in HO-1-mediated immunoprotection. Our previous study characterized the expression profile of Th1 cytokine (IFN- (cid:4) ) and Th2 cytokine (IL-4) in an OVA-in-duced airway hypersensitivity model. OVA challenge suppressed IFN- (cid:4) and increased IL-4. The alteration of Th1/Th2 response was well correlated with the increase of airway resistance. Moreover, hemin significantly reduces IL-4 and airway resistance in the lung and in-creases serum IL-10 level. 26 Thus, it is feasible to postu-late that up-regulation of IL-10 by HO-1 is involved in balancing Th1/Th2 reaction as evidenced by the protective effect of hemin. To further define the role of IL-10 in HO-1-mediated immunoregulation, we studied the protective effect of hemin in IL-10-deficient animals. Compared to wild-type mice with the same genetic back-ground, hemin was unable to lessen the IgE production and airway inflammation elicited by OVA in B6.129P2-Il 10 tm1Cgn /J mice. This is further supported by the fact that IL-10-deficient Treg cells failed to suppress T-cell proliferation. Meanwhile, we consider that IL-10 may have multiple roles in HO-1-mediated anti-inflammatory pro-cess, including up-regulation of foxp3 and direct suppression of inflammatory responses. Here we have showed that induction of HO-1 by hemin mitigated airway inflammation in OVA-induced asthmatic model. The im-munoregulatory effect of HO-1 is in part mediated by IL-10.Insummary, our study has demonstrated that HO-1 can directly up-regulate foxp3 in CD4 (cid:1) CD25 (cid:1) Treg cells.