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Genetic makeup of the host plays a significant role in the course and outcome of infection. Inbred strains of mice display a wide range of sensitivities to Listeria monocytogenes infection and thus serve as a good model for analysis of the effect of genetic polymorphism. The outcome of L. monocytogenes infection in mice is influenced by the ability of this bacterium to induce expression of interferon beta mRNA, encoded in mouse by the Ifnb1 (interferon beta 1, fibroblast) gene. Mouse strains that lack components of the IFN beta signaling pathway are substantially more resistant to infection. We found that macrophages from the ByJ substrain of the common C57BL/6 inbred strain of mice are impaired in their ability to induce Ifnb1 expression in response to bacterial and viral infections. We mapped the locus that controls differential expression of Ifnb1 to a region on Chromosome 7 that includes interferon regulatory factor 3 (Irf3), which encodes a transcription factor responsible for early induction of Ifnb1 expression. In C57BL/6ByJ mice, Irf3 mRNA was inefficiently spliced, with a significant proportion of the transcripts retaining intron 5. Analysis of the Irf3 locus identified a single base-pair polymorphism and revealed that intron 5 of Irf3 is spliced by the atypical U12-type spliceosome. We found that the polymorphism disrupts a U12-type branchpoint and has a profound effect on the efficiency of splicing of Irf3. We demonstrate that a naturally occurring change in the splicing control element has a dramatic effect on the resistance to L. monocytogenes infection. Thus, the C57BL/6ByJ mouse strain serves as an example of how a mammalian host can counter bacterial virulence strategies by introducing subtle alteration of noncoding sequences.

Background: Transmission-blocking vaccine (TBV) is a promising strategy for interrupting the malaria transmission cycle. Current TBV candidates include both pre- and post-fertilization antigens expressed during sexual development of the malaria parasites. Methods: We tested whether a TBV design combining two sexual-stage antigens has better transmission-blocking activity. Using the rodent malaria model Plasmodium yoelii, we pursued a DNA vaccination strategy with genes encoding the gametocyte antigen Pys48/45 and the major ookinete surface protein Pys25. Results: Immunization of mice with DNA constructs expression either Pys48/45 or Pys25 elicited strong antibody responses, which specifically recognized a ~45 and ~25 kDa protein from gametocyte and ookinete lysates, respectively. Immune sera from mice immunized with DNA constructs expressing Pys48/45 and Pys25 individually and in combination displayed evident transmission-blocking activity in in vitro ookinete culture and direct mosquito feeding experiments. With both assays, the Pys25 sera had higher transmission-blocking activity than the Pys48/45 sera. Intriguingly, compared with the immunization with the individual DNA vaccines, immunization with both DNA constructs produced lower antibody responses against individual antigens. The resultant immune sera from the composite vaccination had significantly lower transmission-blocking activity than those from Pys25 DNA immunization group, albeit the activity was substantially higher than that from the Pys48 DNA vaccination group. Conclusions: This result suggested that vaccination with the two DNA constructs did not achieve a synergistic effect, but rather caused interference in inducing antigen-specific antibody responses. This result has important implications for future design of composite vaccines targeting different sexual antigens. [ABSTRACT FROM AUTHOR]

L-Arginine (L-Arg), the substrate for nitric oxide (NO) synthase, has been used to treat malaria to reverse endothelial dysfunction in adults. However, the safety and efficacy of L-Arg remains unknown in malaria patients under the age of five, who are at the greatest risk of developing cerebral malaria (CM), a severe malaria complication. Here, we tested effects of L-Arg treatment on the outcomes of CM using a mouse model. Experimental cerebral malaria (ECM) was induced in female C57BL/6 mice infected with Plasmodium berghei ANKA, and L-Arg was administrated either prophylactically or after parasite infection. Surprisingly, both types of L-Arg administration caused a decline in survival time and raised CM clinical scores. L-Arg treatment increased the population of CD4+T-bet+IFN-γ + Th1 cells and the activated macrophages (F4/80+CD36+) in the spleen. The levels of pro-inflammatory cytokines, IFN-γ and TNF-α, in splenocyte cultures were also increased by L-Arg treatment. The above changes were accompanied with a rise in the number of dendritic cells (DCs) and an increase in their maturation. However, L-Arg did not affect the population of regulatory T cells or the level of IL-10 in the spleen. Taken together, these data suggest that L-Arg may enhance the Th1 immune response, which is essential for a protective response in uncomplicated malaria but could be lethal in CM patients. Therefore, the prophylactic use of L-Arg to treat CM, based on the assumption that restoring the bioavailability of endothelial NO improves the outcome of CM, may need to be reconsidered especially for children. [ABSTRACT FROM AUTHOR]

Chloroquine (CQ), a well-known anti-malarial drug, has long been used for the treatment of autoimmune diseases because of its profound immunomodulatory effects. However, whether this drug modifies antimalaria immune response is still not clear. Here we studied the immunomodulatory role of CQ in a mouse model of malaria. DBA/2 mice were infected with Plasmodium yoelii (Py) parasite (intraperitoneal injection of parasitized erythrocytes) and divided into three groups. Two groups received single dose of CQ (gavage administration) at 6 hours after Py infection (post-6h) and 3 days after Py infection (post-3d), respectively. The third group received saline as control. The course of disease was monitored and the changes of immune response were investigated. It is shown that mice from the post-6h group took longer time to clear the parasites compared with those of the post-3d group. The activation of T helper cells, macrophages, and B cells was significantly suppressed in mice with post-6h CQ treatment as compared with control mice on day 3 and day 5 after infection. In contrast, no such changes were found in mice from the post-3d group. Dendritic cells (DCs) from the post-6h CQ treated mice were less mature as compared with those from control mice as well as those from the post-3d group. Taken together, our data suggest that treatment with CQ early in infection inhibits protective immune response against Py infection possibly via mechanisms involving the modulation of DC's function. Our finding provided important information for reasonable use of CQ in malaria chemotherapy. [ABSTRACT FROM AUTHOR]

The present study aimed to investigate the signal transduction mechanism of the NZW type interleukin (IL)-10R1 and the effect on the function of B lymphocytes. Vectors for the expression of wild-type, NZW and G1146A IL-10R1 were constructed and transfected into Ba/F3 cells. The cell proliferation curve was determined using an MTT assay. CD32 and leukocyte-endothelial cell adhesion molecule 1 (LECAM-1) expression levels were assessed using flow cytometry. The phosphorylation of Janus kinase 1 (Jak1), tyrosine kinase 2 (Tyk2) and signal transducer and activator of transcription 3 (Stat3) were measured by western blot analysis. As compared with wild-type IL-10R1 cells, the proliferation ability of NZW IL-10R1 cells was increased following stimulation with IL-10, which was even greater for G1146A cells. CD32 levels in NZW IL-10R1 cells were lower, while the expression of LECAM-1 was higher compared with wild-type IL-10R1 cells, which was also observed for G1146A cells. The phosphorylation levels of Jak1 and Stat3 in NZW IL-10R1 and G1146A IL-10R1 cells were significantly lower compared with the wild-type IL-10R1 cells. However, the phosphorylation levels in the three cell types were not significantly different. In conclusion, the deficiency in Jak1-Stat3 signal transduction in NZW IL-10R1 cells induces a loss in the inhibition ability of proliferation and activation as well as a migration tendency of B lymphocytes, which is hypothesized to be associated with the occurrence and development of the autoimmune disease systemic lupus erythematosus (SLE). [ABSTRACT FROM AUTHOR]

Listeria monocytogenes (Lm) has been used as the adjuvant or vector for tumor and viral vaccine for its capability of eliciting all aspects of cell-mediated immunity including T cell activation and interferon-gamma (IFN-γ ) production. These effector components play critical roles in the protection against Plasmodium infection in both human malaria and mouse models. Therefore, immune response induced by Lm infection may benefit the defense against malaria. To test this hypothesis, we employed blood-stage Plasmodium yoelii (PyL) infected mice and challenged them with Lm. C57BL/6 and BALB/c mice that are sensitive to PyL infection were used in experiments. These two strains are resistant and sensitive, respectively, to Lm infection. The outcomes of double infection with PyL and Lm and the changes of immune response were investigated. We found that live Lm inoculation inhibited PyL multiplication in both C57BL/6 and BALB/c mice. Lm inoculation increased production of IFN-γ , infiltration of CD11b-positive macrophages and generation of nitric oxide in the spleen of C57BL/6 mice at day 5 after parasite infection. Both CD4- and CD8- positive T cells contributed to IFN-γ production induced by Lm inoculation in PyL-infected mice. The protective effect of Lm against PyL infection depended on the viability of the bacteria. Live Lm, rather than heat-killed Lm, stimulated early IFN-γ production which provided essential cytokine environment for the development of Th1 response in PyL-infected mice. Our data show for the first time that Lm inoculation has protective effect against blood-stage murine malaria, which provides a new clue for enhancing anti- Plasmodium immunity. [ABSTRACT FROM AUTHOR]

Genetic makeup of the host plays a significant role in the course and outcome of infection. Inbred strains of mice display a wide range of sensitivities to Listeria monocytogenes infection and thus serve as a good model for analysis of the effect of genetic polymorphism. The outcome of L. monocytogenes infection in mice is influenced by the ability of this bacterium to induce expression of interferon beta mRNA, encoded in mouse by the Ifnb1 (interferon beta 1, fibroblast) gene. Mouse strains that lack components of the IFNb signaling pathway are substantially more resistant to infection. We found that macrophages from the ByJ substrain of the common C57BL/6 inbred strain of mice are impaired in their ability to induce Ifnb1 expression in response to bacterial and viral infections. We mapped the locus that controls differential expression of Ifnb1 to a region on Chromosome 7 that includes interferon regulatory factor 3 (Irf3), which encodes a transcription factor responsible for early induction of Ifnb1 expression. In C57BL/6ByJ mice, Irf3 mRNA was inefficiently spliced, with a significant proportion of the transcripts retaining intron 5. Analysis of the Irf3 locus identified a single base-pair polymorphism and revealed that intron 5 of Irf3 is spliced by the atypical U12-type spliceosome. We found that the polymorphism disrupts a U12-type branchpoint and has a profound effect on the efficiency of splicing of Irf3. We demonstrate that a naturally occurring change in the splicing control element has a dramatic effect on the resistance to L. monocytogenes infection. Thus, the C57BL/6ByJ mouse strain serves as an example of how a mammalian host can counter bacterial virulence strategies by introducing subtle alteration of noncoding sequences. [ABSTRACT FROM AUTHOR]

In animal models of experimental cerebral malaria (ECM), neuropathology is associated with an overwhelming inflammatory response and sequestration of leukocytes and parasite-infected RBCs in the brain. In this study, we explored the effect of vitamin D (VD; cholecalciferol) treatment on host immunity and outcome of ECM in C57BL/6 mice during Plasmodium berghei ANKA (PbA) infection. We observed that oral administration of VD both before and after PbA infection completely protected mice from ECM. VD administration significantly dampened the inducible systemic inflammatory responses with reduced circulating cytokines IFN-γ and TNF and decreased expression of these cytokines by the spleen cells. Meanwhile, VD also resulted in decreased expression of the chemokines CXCL9 and CXCL10 and cytoadhesion molecules (ICAM-1, VCAM-1, and CD36) in the brain, leading to reduced accumulation of pathogenic T cells in the brain and ultimately substantial improvement of the blood-brain barriers of PbA-infected mice. In addition, VD inhibited the differentiation, activation, and maturation of splenic dendritic cells. Meanwhile, regulatory T cells and IL-10 expression levels were upregulated upon VD treatment. These data collectively demonstrated the suppressive function of VD on host inflammatory responses, which provides significant survival benefits in the murine ECM model. [ABSTRACT FROM AUTHOR]