Immunostimulatory oligonucleotides in therapy of allergic diseases

Optimization of allergen standardization

Preparation of high quality allergen extracts is essential for the diagnosis and immunotherapy of allergic disorders. Standardization of allergen extracts concerns determination of the allergen unit, development of reference material and measurement of the overall IgE binding capacity of an allergen extract. Recently, quantification of individual allergens has been the main focus of allergen standardization because the allergenicity of most allergen extracts is known to be mainly dependent on the content of a small number of allergen molecules. Therefore, characterization of major allergens will facilitate the standardization of allergens. In this article, we review the current state of allergen standardization. In addition, we briefly summarize the components of allergen extracts that should be under control for the optimization of allergen standardization, since its adjuvant-like activities could play an important role in allergic reactions even though the molecule itself does not bind to the IgE antibodies from subjects.

Immune Mechanisms and Therapeutic Potential of CpG Oligodeoxynucleotides

Unmethylated CpG motifs in bacterial DNA and synthetic oligodeoxynucleotides activate immune cells that express Toll-like Receptor 9. Activation through this receptor triggers cellular signaling that leads to production of a proinflammatory and a Th1-type, antigen-specific immune response. The immunostimulatory effects of CpG oligodeoxynucleotides confer protection against infectious disease, allergy and cancer in animal models, and clinical trials have been initiated. However, CpG oligodeoxynucleotides may exacerbate disease in some situations. We will review current concepts in the mechanisms of activating Toll-like Receptor 9 with CpG oligodeoxynucleotides and highlight opportunities for using large animal models to better determine the mechanisms of action.

Innate immunity in the paranasal sinuses: a review of nasal host defenses

BACKGROUND

Chronic rhinosinusitis (CRS) is a common inflammatory disorder of the paranasal sinuses. An abnormal host response to common bacterial or fungal pathogens is thought to be an important factor in the disease process. Host sinonasal epithelium plays an important role in initially recognizing the presence of microbes and responding by increasing production of antimicrobial peptides and cytokines, with recruitment of phagocytes and lymphocytes of the adaptive immune system, to eliminate the infection. Recently, the innate immune system and its complex interplay with the adaptive immune system are increasingly being recognized as important in the pathogenesis of chronic inflammatory diseases such as asthma and CRS.

METHODS

Review of recent findings on innate immunity in the pathogenesis of CRS.

RESULTS

New areas of research into potentially novel therapies for CRS are highlighted in this review, with emphasis on toll-like receptors, antimicrobial peptides (cathelicidins and defensins), and surfactant proteins.

CONCLUSION

This review provides an overview of innate immunity in the sinonasal tract and discusses potential use of innate immune peptides as treatments against fungi, biofilms, and superantigens in CRS.

Reduction of TLR2 gene expression in allergic and nonallergic rhinitis

BACKGROUND

Immunomodulators, including toll-like receptors (TLRs) and defensins, produced in response to pathogenic stimuli, can direct the developing immune system toward a T(H)1 nonallergic phenotype. Increased human beta-defensin (HBD) 4 expression is associated with infection.

OBJECTIVE

To determine whether reduced mucosal levels of TLRs and defensins contribute to the inflammation seen in chronic allergic and nonallergic rhinitis.

METHODS

Real-time polymerase chain reaction was used to determine gene expression levels of HBDs 1 through 4 and TLRs 2 and 4. Immunohistochemical analysis was used to study the localization and distribution of protein for alpha-defensins 1 through 3, HBD2, neutrophil elastase, and TLR2 in sections of nasal turbinate tissue from adults with persistent allergic and idiopathic rhinitis, healthy nasal mucosa, and tonsil tissue.

RESULTS

Allergic mucosa showed a significant (P = .02) reduction in TLR2 messenger RNA expression compared with control mucosa and generally reduced expression for TLR4 and HBDs. Although not significant, the nonallergic group also showed reduced expression for TLRs and HBDs. With the exception of HBD4, increased target gene levels were seen in tonsil tissue. Protein expression of HBD2 and TLR2 was localized in lining and submucosal glandular epithelium but insignificant differences were seen for HBDs, TLRs, neutrophils, and a-defensin between the rhinitic and control patient groups.

CONCLUSIONS

Subjects with allergic and nonallergic rhinitis show reduced TLR and HBD gene expression. The significant reduction in TLR2 gene expression in allergic adults supports the concept that increased TLR2 protects against the development of allergy. The low levels of HBD4 detected in both rhinitis groups suggest lack of an underlying infection pathophysiological feature.

Nucleic acids exert a sequence-independent cooperative effect on sequence-dependent activation of Toll-like receptor 9

Toll-like receptor 9 (TLR9) activates the innate immune system in response to microbial DNA or mimicking oligodeoxynucleotides. Although cell stimulation experiments demonstrate the preferential activation of TLR9 by CpG-containing nucleic acids, direct binding investigations have reached contradictory conclusions with respect to the ability of this receptor to bind nucleic acids in a sequence-specific manner. To address this apparent discrepancy, we report the purification of the soluble ectodomain of human TLR9 with characterization of its ligand binding properties. We observe that TLR9 has a high degree of specificity in its ability to bind nucleic acids that contain CpG dinucleotides as well as higher order motifs that mediate species-specific activation. However, TLR9 is also functionally influenced by nucleic acids in a sequence-independent fashion as both stimulatory and nonstimulatory nucleic acids sensitize TLR9 for in vitro ligand binding as well as in vivo activation. We propose a model in which receptor activation is achieved in a sequence-dependent manner, and sensitivity is modulated by the absolute concentration of nucleic acids in a sequence-independent fashion. This model bears resemblance to that recently proposed for Toll in that activation is a two-step process in which formation of a ligand-bound monomer precedes formation of the activated dimer. In each model receptor sensitivity is determined within the second step with the crucial distinction that Toll undergoes negative cooperativity, whereas TLR9 is sensitized through a positive cooperative effect.

Regulatory T cells: which role in the pathogenesis and treatment of allergic disorders?

Several recent data suggest the importance of different types of cells in the regulation of T-cell effector-mediated immune responses. However, a unique specific marker for these cells has not yet been identified. Moreover, in addition to a dedicated functional lineage, even a 'plastic' phenotype of regulatory T cells seems to exist. The lack of a unique specific marker for regulatory T cells, as well as their heterogeneity, make it difficult to determine whether a defect of regulatory T cells plays a role in the pathogenesis of common allergic disorders. Novel therapeutic strategies based on the induction or potentiation of regulatory T cells able to hamper allergic inflammatory reactions are desirable, but their possible efficacy and safety are not yet known. At present, therapeutic strategies able to induce an immune deviation of allergen-specific type 2 T-helper responses to a less polarized phenotype rather than a general immune suppression appear more realistic.