The impaired Th1 immune response of C3HeB/FeJ mice infected with Leishmania amazonensis: lessons learned from immunotherapy and vaccines

Leishmaniasis is a zoonotic disease caused by intracellular protozoan parasites of the genus Leishmania. Leishmania major and Leishmania amazonensis are both causative agents of cutaneous leishmaniasis in the Old and New World, respectively. While C3H mice are resistant to a L. major infection, they are susceptible to a L. amazonensis challenge and this is characterized by the development of chronic cutaneous lesions. Resistance to L. major is mediated by a T helper 1 (Th1) immune response characterized by CD4+ T cells producing IFN-gamma. In contrast, the susceptibility to L. amazonensis is associated with an impaired Th1 response and CD4 + T cell defects. Dendritic cells (DC) are the most potent antigen-presenting cells in vitro and in vivo and they have been used successfully as vaccine adjuvants to promote Th1 response in mouse studies of Leishmania spp. infection. Our hypothesis was that the induction of a Th1 response in C3H mice would promote resistance to a subsequent L. amazonensis challenge. Using a DC-based immunotherapy, we were able to induce a Th1 response in mice chronically infected with L. amazonensis. However, this did not mediate healing of the infection. When given before infection, a DC-based vaccine also promoted a Th1 response but it was not protective against a subsequent L. amazonensis promastigote challenge. Taken together, this data suggested that a Th1 response may not mediate resistance to L. amazonensis infection. However, we also show that the Th1 response elicited in C3H mice that had healed a previous L. major infection could promote resistance to a subsequent L. amazonensis infection. Therefore, future studies using the immune response of mice that have healed a L. major infection as a model will be needed to determine which immune factors are necessary and/or sufficient to induce protection to a L. amazonensis infection. This will be helpful for the design of future therapeutic and/or vaccine strategies against L. amazonensis

Interplay between CD8α+ Dendritic Cells and Monocytes in Response to Listeria monocytogenes Infection Attenuates T Cell Responses

During the course of a microbial infection, different antigen presenting cells (APCs) are exposed and contribute to the ensuing immune response. CD8α+ dendritic cells (DCs) are an important coordinator of early immune responses to the intracellular bacteria Listeria monocytogenes (Lm) and are crucial for CD8+ T cell immunity. In this study, we examine the contribution of different primary APCs to inducing immune responses against Lm. We find that CD8α+ DCs are the most susceptible to infection while plasmacytoid DCs are not infected. Moreover, CD8α+ DCs are the only DC subset capable of priming an immune response to Lm in vitro and are also the only APC studied that do so when transferred into β2 microglobulin deficient mice which lack endogenous cross-presentation. Upon infection, CD11b+ DCs primarily secrete low levels of TNFα while CD8α+ DCs secrete IL-12 p70. Infected monocytes secrete high levels of TNFα and IL-12p70, cytokines associated with activated inflammatory macrophages. Furthermore, co-culture of infected CD8α+ DCs and CD11b+ DCs with monocytes enhances production of IL-12 p70 and TNFα. However, the presence of monocytes in DC/T cell co-cultures attenuates T cell priming against Lm-derived antigens in vitro and in vivo. This suppressive activity of spleen-derived monocytes is mediated in part by both TNFα and inducible nitric oxide synthase (iNOS). Thus these monocytes enhance IL-12 production to Lm infection, but concurrently abrogate DC-mediated T cell priming

BluePort: A Platform to Study the Eosinophilic Response of Mice to the Bite of a Vector of Leishmania Parasites, Lutzomyia longipalpis Sand Flies

transmission in residents of endemic areas has been attributed to the acquisition of immunity to sand fly salivary proteins. One theoretical way to accelerate the acquisition of this immunity is to increase the density of antigen-presenting cells at the sand fly bite site. Here we describe a novel tissue platform that can be used for this purpose. sand flies. Results presented indicate that a shift in the inflammatory response, from neutrophilic to eosinophilic, is the main histopathological feature associated with the immunity acquired through repeated exposure to the bite of sand flies, and that the BluePort tissue compartment could be used to accelerate this process. In addition, changes observed inside the BluePort parenchyma indicate that it could be used to study complex immunobiological processes, and to develop ectopic secondary lymphoid structures.Understanding the characteristics of the dermal response to the bite of sand flies is a critical element of strategies to control leishmaniasis using vaccines that target salivary proteins. Finding that dermal eosinophilia is such a prominent component of the anti-salivary immunity induced by repeated exposure to sand fly bites raises one important consideration: how to avoid the immunological conflict derived from a protective Th2-driven immunity directed to sand fly saliva with a protective Th1-driven immunity directed to the parasite. The BluePort platform is an ideal tool to address experimentally this conundrum

Plasmodium vivax controlled human malaria infection – progress and prospects

Modern controlled human malaria infection (CHMI) clinical trials have almost entirely focussed on Plasmodium falciparum, providing a highly informative means to investigate host–pathogen interactions as well as assess potential new prophylactic and therapeutic interventions. However, in recent years, there has been renewed interest in Plasmodium vivax, with CHMI models developed by groups in Colombia, the USA, and Australia. This review summarizes the published experiences, and examines the advantages and disadvantages of the different models that initiate infection either by mosquito bite or using a blood-stage inoculum. As for P. falciparum, CHMI studies with P. vivax will provide a platform for early proof-of-concept testing of drugs and vaccines, accelerating the development of novel interventions

The impaired Th1 immune response of C3HeB/FeJ mice infected with Leishmania amazonensis: lessons learned from immunotherapy and vaccines

Leishmaniasis is a zoonotic disease caused by intracellular protozoan parasites of the genus Leishmania. Leishmania major and Leishmania amazonensis are both causative agents of cutaneous leishmaniasis in the Old and New World, respectively. While C3H mice are resistant to a L. major infection, they are susceptible to a L. amazonensis challenge and this is characterized by the development of chronic cutaneous lesions. Resistance to L. major is mediated by a T helper 1 (Th1) immune response characterized by CD4+ T cells producing IFN-gamma. In contrast, the susceptibility to L. amazonensis is associated with an impaired Th1 response and CD4 + T cell defects. Dendritic cells (DC) are the most potent antigen-presenting cells in vitro and in vivo and they have been used successfully as vaccine adjuvants to promote Th1 response in mouse studies of Leishmania spp. infection. Our hypothesis was that the induction of a Th1 response in C3H mice would promote resistance to a subsequent L. amazonensis challenge. Using a DC-based immunotherapy, we were able to induce a Th1 response in mice chronically infected with L. amazonensis. However, this did not mediate healing of the infection. When given before infection, a DC-based vaccine also promoted a Th1 response but it was not protective against a subsequent L. amazonensis promastigote challenge. Taken together, this data suggested that a Th1 response may not mediate resistance to L. amazonensis infection. However, we also show that the Th1 response elicited in C3H mice that had healed a previous L. major infection could promote resistance to a subsequent L. amazonensis infection. Therefore, future studies using the immune response of mice that have healed a L. major infection as a model will be needed to determine which immune factors are necessary and/or sufficient to induce protection to a L. amazonensis infection. This will be helpful for the design of future therapeutic and/or vaccine strategies against L. amazonensis.</p

CD4(+) Th1 Cells Induced by Dendritic Cell-Based Immunotherapy in Mice Chronically Infected with Leishmania amazonensis Do Not Promote Healing

The susceptibility of mice to Leishmania amazonensis infection is thought to result from an inability to develop a Th1 response. Our data show that the low levels of gamma interferon (IFN-γ) produced by the draining lymph node (DLN) cells of chronically infected mice could be enhanced in vitro and in vivo with L. amazonensis antigen-pulsed bone marrow-derived dendritic cells (BM-DC) and the Th1-promoting cytokine interleukin-12 (IL-12). Given intralesionally to chronically infected mice, this treatment induced the upregulation of mRNA levels for IFN-γ, the transcription factor T-box expressed in T cells, and IL-12 receptor β2 in CD4(+) T cells from the DLN and an increase in parasite-specific immunoglobulin G2a in the serum. However, this Th1 response was not associated with healing, and the antigen-specific enhancement of IFN-γ production remained impaired in the DLN. However, addition of IL-12 to the in vitro recall response was able to recover this defect, suggesting that antigen-presenting cell-derived IL-12 production may be limited in infected mice. This was supported by the fact that L. amazonensis amastigotes limited the production of IL-12p40 from BM-DC in vitro. Altogether, our data indicate that the immune response of mice chronically infected with L. amazonensis can be enhanced towards a Th1 phenotype but that the presence of Th1 CD4(+) T cells does not promote healing. This suggests that the phenotype of the CD4(+) T cells may not always be indicative of protection to L. amazonensis infection. Furthermore, our data support growing evidence that antigen-presenting cell function, such as IL-12 production, may limit the immune response in L. amazonensis-infected mice

Antigen-Responsive CD4(+) T Cells from C3H Mice Chronically Infected with Leishmania amazonensis Are Impaired in the Transition to an Effector Phenotype

C3HeB/FeJ mice challenged with Leishmania major develop a polarized Th1 response and subsequently heal, whereas Leishmania amazonensis challenge leads to chronic lesions with high parasite loads at 10 weeks postinfection. In this study, a comparison of draining lymph node cells from L. amazonensis- and L. major-infected mice at 10 weeks postinfection showed equivalent percentages of effector/memory phenotype CD44(hi) CD4(+) T cells producing interleukin-2 (IL-2) and proliferating after antigen stimulation. However, these cells isolated from L. amazonensis-infected mice were not skewed toward either a Th1 or Th2 phenotype in vivo, as evidenced by their unbiased Th1/Th2 transcription factor mRNA profile. In vivo antigen stimulation with added IL-12 failed to enhance gamma interferon (IFN-γ) production of CD4(+) T cells from L. amazonensis-infected mice. Antigen stimulation of CD4(+) T cells from L. amazonensis-infected mice in vitro in the presence of IL-12 resulted in production of only 10 to 15% of the IFN-γ produced by T cells from L. major-infected mice under identical conditions. These results suggest that the CD4(+) T-cell response during chronic L. amazonensis infection is limited during the transition from an early activated CD4(+) T-cell population to an effector cell population and demonstrate that these T cells have an intrinsic defect beyond the presence or absence of IL-12 during antigen stimulation