Proinflammatory Cytokine Gene Expression in the Stomach Correlates with Vaccine-Induced Protection against Helicobacter pylori Infection in Mice: an Important Role for Interleukin-17 during the Effector Phase

CD4(+) T cells have been shown to be essential for vaccine-induced protection against Helicobacter pylori infection in mice. Less is known about the relative contributions of individual cell subpopulations, such as T(h)1 and T(h)17 cells, and their associated cytokines. The aim of the present study was to find immune correlates to vaccine-induced protection and further study their role in protection against H. pylori infection. Immunized and unimmunized mice were challenged with H. pylori, and immune responses were compared. Vaccine-induced protection was assessed by measuring H. pylori colonization in the stomach. Gastric gene expression of T(h)1- and/or T(h)17-associated cytokines was analyzed by quantitative PCR, and contributions of individual cytokines to protection were evaluated by antibody-mediated in vivo neutralization. By analyzing immunized and unimmunized mice, a significant inverse correlation between the levels of interleukin-12p40 (IL-12p40), tumor necrosis factor alpha (TNF), gamma interferon (IFN-gamma), and IL-17 gene expression and the number of H. pylori bacteria in the stomachs of individual animals after challenge could be demonstrated. In a kinetic study, upregulation of TNF, IFN-gamma, and IL-17 coincided with vaccine-induced protection at 7 days after H. pylori challenge and was sustained for at least 21 days. In vivo neutralization of these cytokines during the effector phase of the immune response revealed a significant role for IL-17, but not for IFN-gamma or TNF, in vaccine-induced protection. In conclusion, although both T(h)1- and T(h)17-associated gene expression in the stomach correlate with vaccine-induced protection against H. pylori infection, our study indicates that mainly T(h)17 effector mechanisms are of critical importance to protection.