The debate over the effector function of eosinophils in helminth infection: new evidence from studies on the regulation of vaccine immunity by IL-12.
The production of Th1-type cytokines is associated with strong cell-mediated immunity while Th2-type cytokines are typically involved in the generation of humoral immune responses. In mice vaccinated a single time (1X) with attenuated cercariae of Schistosoma mansoni, the immunity induced is highly dependent on CD4+ T cells and IFN-gamma. In contrast, mice vaccinated multiple times (3X) have decreased IFN-gamma expression, develop a more dominant Th2-type cytokine response as well as protective antibodies which can passively transfer immunity to naive recipients. Previously, we demonstrated the ability of IL-12, a potent IFN-gamma-inducing cytokine to enhance (1X) schistosome cell-mediated saline-treated mice demonstrated a 70 immunity when administered during the period of immunization. More recently, we asked what effects IL-12 would have on the development humoral-based immunity. While multiply-immunized/ saline-treated mice demonstrated a 70-80% reduction in parasite burden, 3X/IL-12-vaccinated animals displayed an even more striking > 90% reduction in challenge infection, with many mice in the later group demonstrating complete protection. Analysis of pulmonary cytokine mRNA responses demonstrated that control challenged mice elicited a dominant Th2-type response, 3X/saline-vaccinated produced a mixed Th1/Th2-type cytokine response, while 3X/IL-12-immunized animals displayed a dominant Th1-type response. The IL-12-treated group also showed a marked reduction in total serum IgE and tissue eosinophilia while SWAP-specific IgG2a and IgG2b Abs were elevated. Interestingly, animals vaccinated with IL-12 also showed a highly significant increase in total Ig titers specific for IrV, a known protective antigen. More importantly, 3X/IL-12 serum transferred significantly less protection. Nevertheless, animals vaccinated in the presence of IL-12 also develop macrophages with enhanced nitric oxide dependent killing activity against the parasites. Together, these observation suggest that IL-12, initially described as an adjuvant for cell-mediated immunity, may also be used as an adjuvant for promoting both humoral and cell-mediated protective responses.
Immunobiology Section, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland 20892, USA.
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Wynn
D000818:Animals; D016207:Cytokines / Q000502:physiology; D004804:Eosinophils / Q000502:physiology*; D006373:Helminthiasis / Q000276:immunology; D018664:Interleukin-12 / Q000502:physiology; D051379:Mice; D012550:Schistosoma mansoni / Q000276:immunology; D018417:Th1 Cells; D018418:Th2 Cells; D014613:Vaccines, Attenuated
D016207:Cytokines; D014613:Vaccines, Attenuated; D018664:Interleukin-12