Roles of CD122+ cells in resistance against Neospora caninum infection in a murine model

From Signaling Pathways to Distinct Immune Responses: Key Factors for Establishing or Combating Neospora caninum Infection in Different Susceptible Hosts

: Neospora caninum is an intracellular protozoan parasite affecting numerous animal species. It induces significant economic losses because of abortion and neonatal abnormalities in cattle. In case of infection, the parasite secretes numerous arsenals to establish a successful infection in the host cell. In the same context but for a different purpose, the host resorts to different strategies to eliminate the invading parasite. During this battle, numerous key factors from both parasite and host sides are produced and interact for the maintaining and vanishing of the infection, respectively. Although several reviews have highlighted the role of different compartments of the immune system against N. caninum infection, each one of them has mostly targeted specific points related to the immune component and animal host. Thus, in the current review, we will focus on effector molecules derived from the host cell or the parasite using a comprehensive survey method from previous reports. According to our knowledge, this is the first review that highlights and discusses immune response at the host cell-parasite molecular interface against N. caninum infection in different susceptible hosts.

Neospora caninum Dense Granule Protein 7 Regulates the Pathogenesis of Neosporosis by Modulating Host Immune Response

Neospora caninum is a protozoan parasite closely related to Toxoplasma gondii Neosporosis caused by N. caninum is considered one of the main causes of abortion in cattle and nervous-system dysfunction in dogs, and identification of the virulence factors of this parasite is important for the development of control measures. Here, we used a luciferase reporter assay to screen the dense granule proteins genes of N. caninum, and we found that NcGRA6, NcGRA7, and NcGRA14 are involved in the activation of the NF-κB, calcium/calcineurin, and cAMP/PKA signals. To analyze the functions of these proteins and Neospora cyclophilin, we successfully knocked out their genes in the Nc1 strain using plasmids containing the CRISPR/Cas9 components. Among the deficient lines, the NcGRA7-deficient parasites showed reduced virulence in mice. An RNA sequencing analysis of infected macrophage cultures showed that NcGRA7 mainly regulates the host cytokine and chemokine production. The levels of gamma interferon in the ascites fluid, CXCL10 expression in the peritoneal cells, and CCL2 expression in the spleen were lower 5 days after infection with the NcGRA7-deficient parasite than after infection with the parental strain. The parasite burden and the degree of necrosis in the brains of mice infected with the NcGRA7-deficient parasite were also lower than in those of the parental strain. Collectively, our data suggest that both the NcGRA7-dependent activation of the inflammatory response and the parasite burden are important in Neospora virulence.IMPORTANCENeospora caninum invades and replicates in a broad range of host species and cells within those hosts. The effector proteins exported by Neospora induce its pathogenesis by modulating the host immunity. We show that most of the transcriptomic effects in N. caninum-infected cells depend upon the activity of NcGRA7. A deficiency in NcGRA7 reduced the virulence of the parasite in mice. This study demonstrates the importance of NcGRA7 in the pathogenesis of neosporosis.

The therapeutic T-cell response induced by tumor delivery of TNF and melphalan is dependent on early triggering of natural killer and dendritic cells

The fusion protein L19mTNF (mouse TNF and human antibody fragment L19 directed to fibronectin extra domain B) selectively targets the tumor vasculature, and in combination with melphalan induces a long-lasting T-cell therapeutic response and immune memory in murine models. Increasing evidence suggests that natural killer (NK) cells act to promote effective T-cell-based antitumor responses. We have analyzed the role of NK cells and dendritic cells (DCs) on two different murine tumor models: WEHI-164 fibrosarcoma and C51 colon carcinoma, in which the combined treatment induces high and low rejection rates, respectively. In vivo NK-cell depletion strongly reduced the rejection of WEHI-164 fibrosarcoma and correlated with a decrease in mature DCs, CD4+ , and CD8+ T cells in the tumor-draining LNs and mature DCs and CD4+ T cells in the tumor 40 h after initiation of the therapy. NK-cell depletion also resulted in the impairment of the stimulatory capability of DCs derived from tumor-draining LNs of WEHI-164-treated mice. Moreover, a significant reduction of M2-type infiltrating macrophages was detected in both tumors undergoing therapy. These results suggest that the efficacy of L19mTNF/melphalan therapy is strongly related to the early activation of NK cells and DCs, which are necessary for an effective T-cell response.

Predominant role of interferon-γ in the host protective effect of CD8(+) T cells against Neospora caninum infection

It is well established that CD8⁺ T cells play an important role in protective immunity against protozoan infections. However, their role in the course of Neospora caninum infection has not been fully elucidated. Here we report that CD8-deficient mice infected with N. caninum presented higher parasitic loads in the brain and lungs and lower spleen and brain immunity-related GTPases than their wild-type counterparts. Moreover, adoptive transfer of splenic CD8⁺ T cells sorted from N. caninum-primed immunosufficient C57BL/10 ScSn mice prolonged the survival of infected IL-12-unresponsive C57BL/10 ScCr recipients. In both C57BL/6 and C57BL/10 ScSn mice CD8⁺ T cells are activated and produce interferon-γ (IFN-γ) upon challenged with N. caninum. The host protective role of IFN-γ produced by CD8⁺ T cells was confirmed in N. caninum-infected RAG2-deficient mice reconstituted with CD8⁺ T cells obtained from either IFN-γ-deficient or wild-type donors. Mice receiving IFN-γ-expressing CD8⁺ T cells presented lower parasitic burdens than counterparts having IFN-γ-deficient CD8⁺ T cells. Moreover, we observed that N. caninum-infected perforin-deficient mice presented parasitic burdens similar to those of infected wild-type controls. Altogether these results demonstrate that production of IFN-γ is a predominant protective mechanism conferred by CD8⁺ T cells in the course of neosporosis.

Role of the chemokine receptor CCR5-dependent host defense system in Neospora caninum infections

Background

Neospora caninum, a Toxoplasma gondii-like obligate intracellular parasite, causes abortion in cattle and neurological signs in canines. To understand neosporosis better, studies on host cell migration and host immune responses during the early phase of infection are important. Although the C-C chemokine receptor 5 (CCR5) plays a crucial role in immune cell migration, the role played by it in protective immunity against N. caninum is poorly understood.

Methods

CCR5^−/− mice were used to investigate their sensitivity levels to N. caninum infection and their ability to activate immune cells against this parasite.

Results

Increased mortality and neurological impairment were observed in the N. caninum-infected CCR5^−/− mice. In comparison with wild-type mice, CCR5^−/− mice experienced poor migration of dendritic cells and natural killer T cells to the site of infection. Dendritic cells in an in vitro culture from CCR5^−/− mice could not be activated upon infection with N. caninum. Furthermore, higher levels of IFN-γ and CCL5 expression, which are associated with brain tissue damage, were observed in the brain tissue of CCR5^−/− mice during the acute phase of the infection, while there was no significant difference in the parasite load between the wild-type and CCR5^−/− animals. Additionally, a primary microglia culture from CCR5^−/− mice showed lower levels of IL-6 and IL-12 production against N. caninum parasites.

Conclusions

Our findings show that migration and activation of immune cells via CCR5 is required for controlling N. caninum parasites during the early phase of the infection.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-014-0620-5) contains supplementary material, which is available to authorized users.

Macrophage depletion prior to Neospora caninum infection results in severe neosporosis in mice

We observed that murine macrophages showed greater activation and increased interleukin 6 (IL-6), IL-12p40, and interferon gamma (IFN-γ) production during Neospora caninum infection. Many macrophages migrated to the site of infection. Furthermore, macrophage-depleted mice exhibited increased sensitivity to N. caninum infection. This study indicates that macrophages are required for achieving protective immunity against N. caninum.

The immune enhancement of a novel soy lecithin/β-glucans based adjuvant on native Neospora caninum tachyzoite extract vaccine in mice

Efficient, cost-effective and safe Th1-immunity-inducing vaccine formulations are paramount for achieving protection against Neospora caninum. In this study, a new adjuvant (Providean-AVEC) was used in the development of a N. caninum vaccine and evaluated in a mouse model. Soluble N. caninum tachyzoite native protein extract (sNcAg) was selected as vaccine antigen based on its capacity to activate production of pro-inflammatory cytokines on dendritic cells. Vaccines containing 4 and 0.4 μg of sNcAg, and Providean-AVEC, ISCOM-Matrix or aluminum hydroxide (Alum) were tested in BALB/c mice. While mice vaccinated with 4μg of sNcAg + Providean-AVEC developed specific antibodies shortly after the first dose, the rest of the high antigen payload formulations only induced seroconversion after the booster. Mice immunized with the high payload ISCOM vaccine (4 μg sNcAg) or with either low or high payload Providean-AVEC formulations (0.4 μg and 4 μg sNcAg, respectively) elicited higher IgG2a than IgG1 serum levels, and IFN-γ anamnestic responses with a Th1-cytokine biased profile. These animals had no histological signs of cerebral lesions and parasite burden assessed by quantitative real-time PCR was not detected. Vaccine preparations including Providean-AVEC as adjuvant limited N. canimum multiplication even with only a tenth of antigen payload compared to vaccines containing other adjuvants. Using adjuvants to specifically activate dendritic cells, combined with a careful antigen selection can enhance cellular responses to inert N. caninum vaccines.

Immunological characterization of Neospora caninum cyclophilin

Neospora caninum is an intracellular parasite that poses a unique ability to infect a variety of cell types by causing host cell migration. Although previous studies demonstrated that parasite-derived proteins could trigger host cell migration, the related molecules have yet to be determined. Our study aimed to investigate the relationship between Neospora-derived molecules and host cell migration using recombinant protein of N. caninum cyclophilin (NcCyp). Indirect fluorescent antibody test revealed that NcCyp was expressed in the tachyzoite cytosol. Furthermore, NcCyp release from extracellular parasites was detected by sandwich enzyme-linked immunosorbent assay in a time-dependent manner. Recombinant NcCyp caused the cysteine-cysteine chemokine receptor 5-dependent migration of murine and bovine cells. Furthermore, immunohistochemistry indicated that NcCyp was consistently detected in tachyzoites distributed within or around the brain lesions. In conclusion, N. caninum-derived cyclophilin appears to contribute to host cell migration, thereby maintaining parasite/host interactions.

Macrophages are critical for cross-protective immunity conferred by Babesia microti against Babesia rodhaini infection in mice

Although primary infection of mice with Babesia microti has been shown to protect mice against subsequent lethal infection by Babesia rodhaini, the mechanism behind the cross-protection is unknown. To unravel this mechanism, we investigated the influence of primary infection of mice with nonlethal B. microti using different time courses on the outcome of subsequent lethal B. rodhaini infection. Simultaneous infections of mice with these parasites resulted in rapid increases in parasitemia, with 100% mortality in BALB/c mice, as observed with control mice infected with B. rodhaini alone. In contrast, mice with acute, resolving, and chronic-phase B. microti infections were completely protected against B. rodhaini, resulting in low parasitemia and no mortalities. Mice immunized with dead B. microti were not protected from B. rodhaini infection, although high antibody responses were induced. Interestingly, the protected mice had significantly decreased levels of antibody response, cytokines (including gamma interferon [IFN-γ], interleukin-2 [IL-2], IL-8, IL-10, and IL-12), and nitric oxide levels after infection with B. rodhaini. SCID mice and IFN-γ-deficient mice with chronic B. microti infections demonstrated protective responses comparable to those of immunocompetent mice. Likewise, in vivo NK cell depletion did not significantly impair the protective responses. Conversely, macrophage depletion resulted in increased susceptibility to B. rodhaini infection associated with changes in their antibody and cytokines profiles, indicating that macrophages contribute to the protection against this challenge infection. We conclude that future development of vaccines against Babesia should include a strategy that enhances the appropriate activation of macrophages.