The regulatory roles of Th1 and Th2 cells in immune protection against Helicobacter infection are not clearly understood. In this study, we report that a primary H. pylori infection can be established in the absence of IL-12 or IFN-γ. However, IFN-γ, but not IL-12, was involved in the development of gastritis because IFN-γ−/− (GKO) mice exhibited significantly less inflammation as compared with IL-12−/− or wild-type (WT) mice. Both IL-12−/− and GKO mice failed to develop protection following oral immunization with H. pylori lysate and cholera toxin adjuvant. By contrast, Th2-deficient, IL-4−/−, and WT mice were equally well protected. Mucosal immunization in the presence of coadministered rIL-12 in WT mice increased Ag-specific IFN-γ-producing T cells by 5-fold and gave an additional 4-fold reduction in colonizing bacteria, confirming a key role of Th1 cells in protection. Importantly, only protected IL-4−/− and WT mice demonstrated substantial influx of CD4+ T cells in the gastric mucosa. The extent of inflammation in challenged IL-12−/− and GKO mice was much reduced compared with that in WT mice, indicating that IFN-γ/Th1 cells also play a major role in postimmunization gastritis. Of note, postimmunization gastritis in IL-4−/− mice was significantly milder than WT mice, despite a similar level of protection, indicating that immune protection is not directly linked to the degree of gastric inflammation. Only protected mice had T cells that produced high levels of IFN-γ to recall Ag, whereas both protected and unprotected mice produced high levels of IL-13. We conclude that IL-12 and Th1 responses are crucial for H. pylori-specific protective immunity.

In recent years, Abs have been considered a correlate rather than an effector of resistance against Helicobacter pylori infection. However, it is still poorly understood to what extent Ab production correlates with gastric immunopathology. Here we report that Abs not only are dispensable for protection, but they are detrimental to elimination of the bacteria and appear to impair gastric inflammatory responses. We found that the initial colonization with H. pylori bacteria was normal in the B cell-deficient (μMT) mice, whereas at later times (>8 wk) most of the bacteria were cleared, concomitant with the development of severe gastritis. In contrast, wild-type (WT) mice exhibited extensive bacterial colonization and only mild gastric inflammation, even at 16 wk after inoculation. Oral immunizations with H. pylori lysate and cholera toxin adjuvant stimulated comparable levels of protection in μMT and WT mice. The level of protection in both strains correlated well with the severity of the postimmunization gastritis. Thus, T cells were responsible for the gastritis, whereas Abs, including potentially host cell cross-reactive Abs, were not involved in causing the gastritis. The T cells in μMT and WT mice produced high and comparable levels of IFN-γ to recall Ag at 2 and after 8 wk, whereas IL-4 was detected after 8 wk only, indicating that Th1 activity dominated the early phase of protection, whereas later a mixed Th1 and Th2 activity was seen.

Dysfunction of T cells and natural killer (NK) cells has been proposed to deter- IntroductionAcute myeloid leukemia (AML) is characterized by a deficiency of hematopoietic progenitor and stem cell development with a resulting accumulation of immature myeloid cells in BM. [1][2][3] The current treatment in AML comprises an initial phase of intensive chemotherapy, induction, and consolidation that aims to achieve and maintain complete remission (CR). 4,5 Younger patients may subsequently undergo allogeneic stem cell transplantation, 6 whereas few therapeutic options are available in the postconsolidation phase for other patients. 7 The occurrence of relapse after CR along with the poor postrelapse survival significantly explains the dismal longterm survival of patients with AML. 4,8 In several studies investigators point to a role for lymphocytes, such as cytotoxic T cells and natural killer (NK) cells, in the surveillance of the malignant clone in AML and in determining prognosis. 9 T cells are considered to mediate the graft-versusleukemia reaction that significantly accounts for the reduced rate of leukemic relapse after allogeneic stem cell transplantation, 10,11 and several tumor-associated antigens of relevance to T-cell reactivity are expressed by AML cells. 12 A role for NK cells in surveillance of AML cells was demonstrated, as exemplified by the favorable outcome when authors used transplants with donor/recipient class I disparities, which facilitates NK cell-mediated destruction of residual leukemic cells. 13 In addition, multiple deficiencies of T-and NK-cell functions, with ensuing relapse risk and poor prognosis, have been observed in patients with AML who did not undergo transplantation. [14][15][16][17][18] In earlier studies, investigators demonstrated that nonmalignant phagocytic cells down-modulate lymphocyte functions by producing and releasing NADPH oxidase-derived reactive oxygen species (ROS). [19][20][21][22][23] These findings have formed the basis for the use of a NADPH oxidase inhibitor in conjunction with IL-2 as a relapsepreventive strategy in patients with AML. 24,25 In this study, we monitored the surface expression of gp91 phox , a component of the ROS-generating NADPH oxidase, 26 on leukemic cells recovered from BM and blood of newly diagnosed patients with AML and explored whether ROS produced by leukemic cells compromise Tand NK-cell function. These analyses were performed with cells recovered from patients with defined morphologic subtypes of AML cells on the basis of French-American-British (FAB) classification. 27 We report that AML cells from patients with monocytic forms of AML (FAB classes M4/M5), but not cells from patients with myeloblastic AML (FAB class M2) or immature AML (FAB class M1), express the NADPH oxidase, produce ROS, and trigger extensive apoptosis in adjacent T and NK cells. Our results are suggestive of a novel mechanism of immune evasion in myelomonocytic and monocytic AML. Methods Sampling of BM and peripheral bloodPeripheral blood or BM from 26 untreated...

We recently reported that Helicobacter pylori-specific Abs impair the development of gastritis and down-regulate resistance against H. pylori infection. In this study, we asked whether IgA Abs specifically can have an impact on H. pylori colonization and gastric inflammation. To obtain a sensitive model for the study of inflammation we crossed IgA- and IL-10-deficient mice. We found that IL-10−/−/IgA−/− mice were significantly less colonized than IL-10−/−/IgA+/+ mice, which in turn were less colonized than wild-type (WT) mice. The IL-10−/−/IgA−/− mice exhibited a 1.2-log reduction in bacterial counts compared with that in IL-10−/−/IgA+/+ mice, suggesting that IgA Abs rather promoted than prevented infection. The reduced colonization in IL-10−/−/IgA−/− mice was associated with the most severe gastritis observed, albeit all IL-10−/− mice demonstrated more severe gastric inflammation than wild-type mice. The gastritis score and the infiltration of CD4+ T cells into the gastric mucosa were significantly higher in IL-10−/−/IgA−/− mice than in IL-10−/−/IgA+/+ mice, arguing that IgA Abs counteracted inflammation. Moreover, following oral immunization, IL-10−/−/IgA−/− mice were significantly better protected against colonization than IL-10−/−/IgA+/+ mice. However, the stronger protection was associated with more severe postimmunization gastritis and gastric infiltration of CD4+ T cells. There was also a clear increase in complement receptor-expressing cells in IL-10−/−/IgA−/− mice, though C3b-fragment deposition in the gastric mucosa was comparable between the two. Finally, specific T cell responses to recall Ag demonstrated higher levels of IFN-γ production in IL-10−/−/IgA−/− as compared with IL-10−/−/IgA+/+ mice. Thus, it appears that IgA and IL-10 help H. pylori bacteria evade host resistance against infection.

Protective immunity against Helicobacter pylori infection in mice has been associated with a strong Th1 response, involving IL-12 as well as IFN-γ, but recent studies have also demonstrated prominent eosinophilic infiltration, possibly linked to local Th2 activity in the gastric mucosa. In this study we investigated the role of IL-18, because this cytokine has been found to be a coregulator of Th1 development as well as involved in Th2-type responses with local eotaxin production that could influence gastric eosinophilia and resistance to infection. We found that IL-18−/− mice failed to develop protection after oral immunization with H. pylori lysate and cholera toxin adjuvant, indicating an important role of IL-18 in protection. Well-protected C57BL/6 wild-type (WT) mice demonstrated substantial influx of CD4+ T cells and eosinophilic cells in the gastric mucosa, whereas IL-18−/− mice had less gastritis, few CD4+ T cells, and significantly reduced numbers of eosinophilic cells. T cells in well-protected WT mice produced increased levels of IFN-γ and IL-18 to recall Ag. By contrast, unprotected IL-18−/− mice exhibited significantly reduced gastric IFN-γ and specific IgG2a Ab levels. Despite differences in gastric eosinophilic cell infiltration, protected WT and unprotected IL-18−/− mice had comparable levels of local eotaxin, suggesting that IL-18 influences protection via Th1 development and IFN-γ production rather than through promoting local production of eotaxin and eosinophilic cell infiltration.

Reactive oxygen species (ROS) are formed by myeloid cells as a defense strategy against microorganisms. ROS however also trigger poly(ADP-ribose) polymerase 1- (PARP-1) dependent cell death (parthanatos) in adjacent lymphocytes, which has been forwarded as a mechanism of immune escape in several forms of cancer. The present study assessed the role of mitogen-activated protein kinases (MAPKs), in particular the extracellular signal-regulated kinase (ERK), in ROS-induced signal transduction leading to lymphocyte parthanatos. We report that inhibitors of ERK1/2 phosphorylation upheld natural killer (NK) cell-mediated cytotoxicity under conditions of oxidative stress and rescued NK cells and CD8+ T lymphocytes from cell death induced by ROS-producing monocytes. ERK1/2 phosphorylation inhibition also protected lymphocytes from cell death induced by exogenous hydrogen peroxide (H2O2) and from ROS generated by xanthine oxidase or glucose oxidase. Phosphorylation of ERK1/2 was observed in lymphocytes shortly after exposure to ROS. ROS-generating myeloid cells and exogenous H2O2 triggered PARP 1-dependent accumulation of poly ADP-ribose (PAR), which was prevented by ERK pathway inhibitors. ERK1/2 phosphorylation was induced by ROS independently of PARP-1. Our findings are suggestive of a role for ERK1/2 in ROS-induced lymphocyte parthanatos, and that the ERK axis may provide a therapeutic target for the protection of lymphocytes against oxidative stress.

The antibody-dependent cellular cytotoxicity (ADCC) of natural killer (NK) cells is assumed to contribute to the clinical efficacy of monoclonal antibodies (mAbs) in chronic lymphocytic leukemia (CLL) and other hematopoietic malignancies of B cell origin. We sought to determine whether reactive oxygen species (ROS)-producing monocytes regulate the ADCC of NK cells against primary CLL cells using anti-CD20 as the linking antibody. The monoclonal CD20 antibodies rituximab and ofatumumab were found to trigger substantial release of ROS from monocytes. Antibody-exposed monocytes induced NK cell apoptosis and restricted NK cell-mediated ADCC against autologous CLL cells. The presence of inhibitors of ROS formation and scavengers of ROS preserved NK cell viability and restored NK cell-mediated ADCC against primary CLL cells. We propose that limiting the antibody-induced induction of immunosuppressive ROS may improve the anti-leukemic efficacy of anti-CD20 therapy in CLL.

Safe and efficacious adjuvants are much needed to facilitate the development of mucosal vaccines. Here, we have asked whether our nontoxic vaccine adjuvant, CTA1-DD, can enhance protective immunity against Helicobacter pylori infection. Intranasal immunizations with H. pylori lysate together with CTA1-DDadjuvant induced significant protection in C57Bl/6 mice, almost as strong as similar immunizations using cholera toxin (CT)-adjuvant. Protection remained strong even at 8 weeks postchallenge and the bacterial colonization was reduced by 20-fold compared to lysate-immunized controls. Although CTA1-DD was designed to bind to B cells, mMT mice developed significant, but lower, level of protection following immunization. Intranasal immunizations with CT adjuvant in C57Bl/6 mice resulted in the development of severe postimmunization gastritis at 2 and 8 weeks postchallenge, whereas the degree of gastritis was substantially lower in the CTA1-DD-immunized mice. Protection induced by both CTA1-DD-and CT adjuvant was associated with a strong local infiltration of CD4 þ T cells in the gastric mucosa, and recall responses to specific Ag elicited substantial IFN-g production, indicating Th1-dominance. These findings clearly demonstrate that CTA1-DD adjuvant is a promising candidate to be further exploited in the development of a mucosal vaccine against H. pylori infection.