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Prevention of Allergen-Specific, Th2-Biased Immune Responses In Vivo: Role of Increased IL-12 and IL-18 Responsiveness¹

Ian P. Lewkowich^2,*, Julia D. Rempel and Kent T. HayGlass^3,*

^* Department of Immunology and Department of Internal Medicine, Canadian Institutes for Health Research National Training Program in Allergy and Asthma Research, University of Manitoba, Winnipeg, Manitoba, Canada

The factors that control development of adaptive responses to exogenous Ag remain incompletely understood. An ability to selectively direct immunity toward a specific phenotype would be of clinical benefit in numerous immunological disorders. Administration of chemically modified allergen glutaraldehyde-polymerized OVA (OA-POL) leads to >90% reductions in murine IgE and >500-fold increases in IgG2c responses that develop upon subsequent immunization with native Ag. In the present study, we examine the mechanisms underlying this reorientation of the type 2 dominant response that would normally develop. Lack of endogenous IL-12 or IFN- results in markedly reduced induction of IgG2c responses following OA-POL treatment, but only IFN-^–/– mice demonstrate reduced capacity to prevent IgE induction. This indicates that while both IL-12 and IFN- are critical promoters of type 1 immunity, only IFN- is required to maximally inhibit development of type 2 immune responses. Compared with OVA-immunized mice, CD69⁺ T cells from OA-POL-immunized mice demonstrate elevated IL-12R₂, IL-18R, and IL-18R mRNA levels, as well as increased IFN- production in response to rIL-12 or rIL-18 stimulation. Collectively, these data indicate that preventing induction of type 2 immune responses is critically dependent on altered T cell responsiveness to these cytokines. The finding that targeted, Ag-specific manipulation of IL-12 and IL-18 responsiveness can be used to shape the phenotype of the dominant immune response that develops suggests that specifically targeting IL-12 and IL-18 receptor expression may offer clinical options for clinical prophylaxis or intervention.