Jacques A. Louis

Natural Killer Cells Activated by MHC Class ILow Targets Prime Dendritic Cells to Induce Protective CD8 T Cell Responses

Abstract Conserved molecular patterns derived from pathogenic microorganisms prime antigen-presenting dendritic cells (DC) to induce adaptive T cell responses. In contrast, virus-infected or tumor cells that express low levels of major histocompatibility complex (MHC) class I activate natural killer (NK) cells for direct killing. It is unknown whether NK cell recognition of MHC class I low targets can also induce adaptive T cell responses. Here, we show that MHC class I low targets initiate a cascade of immune responses, starting with the immediate activation of NK cells. The activated NK cells then prime DC to produce IL-12 and to induce highly protective CD8 T cell memory responses. Therefore, sensing of MHC class I low targets by NK cells can link innate and adaptive immunity to induce protective T cell responses and may alarm the immune system during early infection with noncytopathic viruses.

IL-4 Rapidly Produced by Vβ4 Vα8 CD4+ T Cells Instructs Th2 Development and Susceptibility to Leishmania major in BALB/c Mice

BALB/c mice develop aberrant T helper 2 (Th2) responses and suffer progressive disease after infection with Leishmania major. These outcomes depend on the production of interleukin-4 (IL-4) early after infection. Here we demonstrate that the burst of IL-4 mRNA, peaking in draining lymph nodes of BALB/c mice 16 hr after infection, occurs within CD4+ T cells that express V beta 4 V alpha 8 T cell receptors. In contrast to control and V beta 6-deficient BALB/c mice, V beta 4-deficient BALB/c mice were resistant to infection, demonstrating the role of these cells in Th2 development. The early IL-4 response was absent in these mice, and T helper 1 responses occurred following infection. Recombinant LACK antigen from L. major induced comparable IL-4 production in V beta 4 V alpha 8 CD4+ cells. Thus, the IL-4 required for Th2 development and susceptibility to L. major is produced by a restricted population of V beta 4 V alpha 8 CD4+ T cells after cognate interaction with a single antigen from this complex organism.

An Immunomodulatory Function for Neutrophils During the Induction of a CD4+ Th2 Response in BALB/c Mice Infected with Leishmania major

The possible immunomodulatory role of polymorphonuclear leukocytes (PMN) in CD4+ T lymphocyte differentiation in mice was examined by studying the effect of transient depletion of PMN during the early phase after Leishmania major delivery. A single injection of the PMN-depleting NIMP-R14 mAb 6 h before infection with L. major prevented the early burst of IL-4 mRNA transcription otherwise occurring in the draining lymph node of susceptible BALB/c mice. Since this early burst of IL-4 mRNA transcripts had previously been shown to instruct Th2 differentiation in mice from this strain, we examined the effect of PMN depletion on Th subset differentiation at later time points after infection. The transient depletion of PMN in BALB/c mice was sufficient to inhibit Th2 cell development otherwise occurring after L. major infection. Decreased Th2 responses were paralleled with partial resolution of the footpad lesions induced by L. major. Furthermore, draining lymph node-derived CD4+ T cells from PMN-depleted mice remained responsive to IL-12 after L. major infection, unlike those of infected BALB/c mice receiving control Ab. PMN depletion had no effect when the NIMP-R14 mAb was injected 24 h postinfection. The protective effect of PMN depletion was shown to be IL-12 dependent, as concomitant neutralization of IL-12 reversed the protective effect of PMN depletion. These results suggest a role for an early wave of PMN in the development of the Th2 response characteristic of mice susceptible to infection with L. major.

IL-4 instructs TH1 responses and resistance to Leishmania major in susceptible BALB/c mice.

Immunity to infection with intracellular pathogens is regulated by interleukin 12 (IL-12), which mediates protective T helper type 1 (TH1) responses, or IL-4, which induces TH2 cells and susceptibility. Paradoxically, we show here that when present during the initial activation of dendritic cells (DCs) by infectious agents, IL-4 instructed DCs to produce IL-12 and promote TH1 development. This TH1 response established resistance to Leishmania major in susceptible BALB/c mice. When present later, during the period of T cell priming, IL-4 induced TH2 differentiation and progressive leishmaniasis in resistant mice. Because immune responses developed via the consecutive activation of DCs and then T cells, the contrasting effects of IL-4 on DC development and T cell differentiation led to immune responses that had opposing functional phenotypes.

The Early IL-4 Response to Leishmania major and the Resulting Th2 Cell Maturation Steering Progressive Disease in BALB/c Mice Are Subject to the Control of Regulatory CD4+CD25+ T Cells

Susceptibility and development of Th2 cells in BALB/c mice infected with Leishmania major result from early IL-4 production by Vβ4Vα8 CD4+ T cells in response to the Leishmania homolog of mammalian RACK1 Ag. A role for CD4+CD25+ regulatory T cells in the control of this early IL-4 production was investigated by depleting in vivo this regulatory T cell population. Depletion induced an increase in the early burst of IL-4 mRNA in the draining lymph nodes of BALB/c mice, and exacerbated the course of disease with higher levels of IL-4 mRNA and protein in their lymph nodes. We further showed that transfer of 107 BALB/c spleen cells that were depleted of CD4+CD25+ regulatory T cells rendered SCID mice susceptible to infection and allowed Th2 differentiation while SCID mice reconstituted with 107 control BALB/c spleen cells were resistant to infection with L. major and developed a Th1 response. Treatment with a mAb against IL-4 upon infection with L. major in SCID mice reconstituted with CD25-depleted spleen cells prevented the development of Th2 polarization and rendered them resistant to infection. These results demonstrate that CD4+CD25+ regulatory T cells play a role in regulating the early IL-4 mRNA and the subsequent development of a Th2 response in this model of infection.

In BALB/c mice, IL-4 production during the initial phase of infection with Leishmania major is necessary and sufficient to instruct Th2 cell development resulting in progressive disease

In contrast to intact BALB/c mice, BALB/c mice rendered deficient in Vβ4+ CD4+ T cells develop a Th1 response to infection with Leishmania major and are resistant. Vβ4-deficient BALB/c mice are unable to generate the early IL-4 transcription occurring in Vβ4 Vα8 CD4+ T cells of BALB/c mice within 1 day of infection. Here we demonstrate that treatment of Vβ4-deficient BALB/c mice with IL-4 during the first 64 h after infection instructs Th2 cell development and susceptibility to infection. The demonstrated inability of IL-4 to reverse the resistant phenotype of BALB/c mice treated with anti-CD4 mAb the day before infection suggest that these effects of IL-4 require its interaction with CD4+ T cells. In contrast to draining lymph node cells from BALB/c mice, cells from Vβ4-deficient BALB/c mice remain responsive to IL-12 following infection. Strikingly, administration of IL-4 to Vβ4-deficient BALB/c mice renders their lymph node cells unresponsive to IL-12 by down-regulating IL-12R β2-chain expression. This study directly demonstrates that in BALB/c mice IL-4 is necessary and sufficient to initiate the molecular events steering Th2 cell maturation and susceptibility to L. major.

Immunization of BALB/c Mice With Helicobacter Urease B Induces a T helper 2 Response Absent in Helicobacter Infection

BACKGROUND & AIMS Infection with Helicobacter induces a T helper type 1 response in mice and humans. Mice can be cured or protected from infection with Helicobacter by mucosal immunization with recombinant H. pylori urease B subunit (rUreB). This study characterizes the immune response of infected mice immunized with rUreB. METHODS BALB/c mice were infected with H. felis. Two weeks later, they were orally immunized four times with rUreB and cholera toxin (CT) at weekly intervals. Controls were only infected or sham-immunized with CT. Animals were killed at various times after immunization. Splenic CD4(+) cells were obtained and cultured in vitro with rUreB to evaluate antigen-specific proliferation and induction of interferon gamma and interleukin 4 secretion. RESULTS All rUreB-immunized mice (n = 8) were cured from infection 3 weeks after the fourth immunization. Immunization induced a proliferative response of splenic CD4(+) cells, a progressive decrease in interferon gamma secretion, and a concomitant increase in interleukin 4 secretion after each immunization. A simultaneous increase in rUreB specific serum immunoglobulin G1 levels was observed in infected/immunized mice. CONCLUSIONS In BALB/c mice, therapeutic mucosal immunization with rUreB induces progressively a Th2 CD4(+) T cell response resulting in the elimination of the pathogen.

Regulation of protective immunity against Leishmania major in mice

Resolution of lesions induced by Leishmania major in mice results from the development of Th1 responses. Cytokines produced by Th1 cells activate macrophages to a parasiticidal state. The development of Th2 responses in mice from a few strains underlies susceptibility to infection. Cytokines produced by Th2 cells exacerbate the development of lesions because of their deactivating properties for macrophages. This murine model of infection has provided significant insight into the mechanisms intrinsic to the differentiation of disparate CD4+ T cell subsets in vivo in animals from different genetic backgrounds.

The resolution of lesions induced by Leishmania major in mice requires a functional Fas (APO‐1, CD 95) pathway of cytotoxicity

Normal of perforin‐deficient C57BL/6 mice are able to heal spontaneously cutaneous lesions induced by Leishmania major. In this report, we show that syngeneic gld and lpr mice, lacking a functional Fas system, fail to heal their lesions. This inability to control infection could not be attributed either to a failure to mount a protective CD4+ Th1 response or to an unresponsiveness of their macrophages to the activating signals of IFN‐γ. The observation showing that administration of exogenous recombinant Fas ligand (FasL) to FasL‐deficient mice resulted in the resolution of cutaneous lesions demonstrates the importance of the Fas‐FasL pathway in the elimination of parasites. Furthermore, macrophages infected with L. major in vitro up‐regulate their surface expression of Fas in response to IFN‐γ and as a result become susceptible to CD4+ T cell‐induced apoptotic death. These results suggest that the CD4+ T cell‐induced apoptotic death of MHC class II‐expressing antigen‐presenting cells, observed in vitro and operating through the Fas (Apo‐1/CD95) pathway, is relevant in vivo.

NKT Cells Are Critical for the Initiation of an Inflammatory Bowel Response against Toxoplasma gondii

We demonstrated in this study the critical role of NKT cells in the lethal ileitis induced in C57BL/6 mice after infection with Toxoplasma gondii. This intestinal inflammation is caused by overproduction of IFN-γ in the lamina propria. The implication of NKT cells was confirmed by the observation that NKT cell-deficient mice (Jα281−/−) are more resistant than C57BL/6 mice to the development of lethal ileitis. Jα281−/− mice failed to overexpress IFN-γ in the intestine early after infection. This detrimental effect of NKT cells is blocked by treatment with α-galactosylceramide, which prevents death in C57BL/6, but not in Jα281−/−, mice. This protective effect is characterized by a shift in cytokine production by NKT cells toward a Th2 profile and correlates with an increased number of mesenteric Foxp3 lymphocytes. Using chimeric mice in which only NKT cells are deficient in the IL-10 gene and mice treated with anti-CD25 mAb, we identified regulatory T cells as the source of the IL-10 required for manifestation of the protective effect of α-galactosylceramide treatment. Our results highlight the participation of NKT cells in the parasite clearance by shifting the cytokine profile toward a Th1 pattern and simultaneously to immunopathological manifestation when this Th1 immune response remains uncontrolled.