Kunihiko Kitagaki

Intestinal helminths protect in a murine model of asthma.

Underdeveloped nations are relatively protected from the worldwide asthma epidemic; the hygiene hypothesis suggests this is due to suppression of Th2-mediated inflammation by increased exposure to pathogens and their products. Although microbial exposures can promote Th2-suppressing Th1 responses, even Th2-skewing infections, such as helminths, appear to suppress atopy, suggesting an alternate explanation for these observations. To investigate whether induction of regulatory responses by helminths may counter allergic inflammation, we examined the effects of helminth infection in a murine model of atopic asthma. We chose Heligosomoides polygyrus, a gastrointestinal nematode, as the experimental helminth; this worm does not enter the lung in its life cycle. We found that H. polygyrus infection suppressed allergen-induced airway eosinophilia, bronchial hyperreactivity, and in vitro allergen-recall Th2 responses in an IL-10-dependent manner; total and OVA-specific IgE, however, were increased by worm infection. Finally, helminth-infected mice were protected against eosinophilic inflammation induced by adoptive transfer of OVA-stimulated CD4+ cells, and transfer of cells from helminth-infected/OVA-exposed mice suppressed OVA-induced eosinophilic inflammation, suggesting a role for regulatory cells. Increased CD4+CD25+Foxp3+ cells were found in thoracic lymph nodes of helminth-infected/OVA-exposed mice. Helminthic colonization appears to protect against asthma and atopic disorders; the regulatory cytokine, IL-10, may be a critical player.

Immunomodulatory Effects of CpG Oligodeoxynucleotides on Established Th2 Responses

ABSTRACT CpG oligodeoxynucleotides (CpG ODNs) are known to induce type 1 T-helper-cell (Th1) responses. We have previously demonstrated that CpG ODNs administered during sensitization prevent Th2-mediated eosinophilic airway inflammation in vivo. We also reported that key Th1 cytokines, gamma interferon (IFN-γ) and interleukin 12 (IL-12), are not necessary for this protection. Recent in vivo data suggest that CpG ODNs might also reverse established pulmonary eosinophilia. In order to clarify how CpG ODNs can inhibit established Th2 responses, we evaluated the cytokine production from splenocytes from antigen- and alum-immunized mice. Restimulation with antigen induced IL-5, which was clearly inhibited by coculture with CpG ODNs in a concentration-dependent manner. CpG ODNs also induced IFN-γ, but in a concentration-independent manner. The inhibition of IL-5 production was not mediated through natural killer cells or via CD8+ T lymphocytes. Although IFN-γ plays an important role in inhibition of antigen-induced IL-5 production by CpG ODNs, IFN-γ was not the sole factor in IL-5 inhibition. CpG ODNs also induced IL-10, and this induction correlated well with IL-5 inhibition. Elimination of IL-10 reduced the anti-IL-5 effect of CpG ODNs, although incompletely. This may be because IFN-γ, induced by CpG ODNs, is also inhibited by IL-10, serving as a homeostatic mechanism for the Th1-Th2 balance. Overproduction of IFN-γ was downregulated by CpG ODN-induced IL-10 via modulation of IL-12 production. These data suggest that CpG ODNs may inhibit established Th2 immune responses through IFN-γ and IL-10 production, the latter serving to regulate excessive Th1 bias. These properties of CpG ODNs might be a useful feature in the development of immunotherapy adjuvants against allergic diseases such as asthma.

CpG DNA and immunotherapy of allergic airway diseases.

Atopic asthma is a highly prevalent and serious health problem for which no therapy currently offers the hope of a cure. Preindustrialized and rural populations appear relatively protected from the asthma epidemic; the hygiene hypothesis ascribes this protection to the effects of microbes and microbial products. An important immunostimulant component of microbes is DNA; bacterial DNA contains sequence motifs centred on the CpG dinucleotide, which are suppressed in mammalian DNA. Oligonucleotides containing these motifs (CpG ODN), like bacterial DNA, promote Th1 and regulatory‐type immune responses. Using CpG ODN, we and others have demonstrated in murine studies that CpG ODN are effective in preventing the development of atopic airways disease. Moreover, when administered in conjunction with experimental allergen, they promote the reversal of established eosinophilic inflammation. These data suggest that CpG ODN may be a novel therapeutic tool for the treatment of atopic asthma.

Modulation of murine allergic rhinosinusitis by CpG oligodeoxynucleotides

Background Allergic rhinosinusitis is characterized by eosinophilic inflammation of the upper airway, which is induced by TH‐2 cytokines. CpG oligodeoxynucleotides (ODN) are known to induce TH‐1 and to suppress TH‐2 cytokines in a variety of settings, including murine models of asthma.

Oral administration of CpG-ODNs suppresses antigen-induced asthma in mice

Oligodeoxynucleotides containing CpG motifs (CpG‐ODNs) can protect against eosinophilic airway inflammation in asthma. Previously we have found that parenteral or mucosal administration of CpG‐ODNs is effective in preventing (as well as reversing established) disease. In this study, we examined the effect of oral CpG‐ODNs on the development of immune tolerance. Using an ovalbumin (OVA)‐induced murine model of asthma, we found that CpG‐ODNs, administered orally around the time of sensitization, prevented eosinophilic airway inflammation in a dose‐dependent manner. Although oral co‐administration of CpG‐ODNs with OVA (known to induce tolerance) did not significantly change the inhibition of OVA‐induced airway eosinophilia, it did modulate OVA‐specific immunoglobulin responses: oral administration of OVA alone suppressed OVA‐specific IgG1 production, but only mice that received CpG‐ODNs demonstrated enhanced levels of OVA‐specific IgG2c. Finally, we examined whether oral administration of CpG‐ODNs, alone or with OVA, could reverse established eosinophilic airway inflammation. Again, neither OVA nor CpG‐ODNs alone modulated established eosinophilic airway inflammation, but a combination of the OVA and CpG‐ODNs successfully desensitized the mice. This desensitization was associated with suppression of OVA‐specific IgE and enhancement of OVA‐specific IgG2c production. These findings provide the first indication that oral administration of CpG‐ODNs is effective in preventing and reversing antigen‐induced eosinophilic airway inflammation. CpG‐ODNs may be useful as a component of oral immunotherapy to promote tolerance in established asthma.

CpG oligodeoxynucleotides in asthma.

Asthma is a major health problem, of which the prevalence and severity are increasing, particularly in industrialized nations. One hypothesis for this is that diminished exposure to childhood infections in modern society has led to decreased Th1-type inflammation. Reduced Th1 responses may lead to enhanced Th2-type inflammation, important in promoting asthma and allergic disease. The most common current treatment for asthma is corticosteroids; while these agents inhibit the function of inflammatory cells, they are ineffective in altering the initial Th2-type response to allergen in a sensitized individual. A novel therapeutic approach, recently reported in the preclinical setting, is the use of oligodeoxynucleotides (ODNs), which contain unmethylated motifs centered on CG dinucleotides. These CpG ODNs potently induce Th1 cytokines and suppress Th2 cytokines, and can prevent manifestations of asthma in animal models. These agents have the potential to reverse Th2-type responses to allergens and thus restore balance to the immune system. Clinical trials are ongoing.