Low and high-dose intradermal infection with Leishmania major and Leishmania amazonensis in C57BL/6 mice

A model of skin infection with Leishmania amazonensis with low doses of parasites is compared to infection with high doses of L. amazonensis and low and high doses of Leishmania major. C57BL/6 mice were infected with 103 or 10(6) parasites in the ear and the outcome of infection was assessed. The appearance of lesions in mice infected with 103 parasites was delayed compared to mice infected with 10(6) Leishmania and parasites were detectable at the infection site before lesions became apparent. Mice infected with L. amazonensis displayed persistent lesions, whereas infection with L. major spontaneously healed in all groups, although lymphocytes persisted at the site of infection after healing. Macrophages persisted only in L. amazonensis-infected mice. High-dose L. amazonensis-infected mice produced lower levels of IFN-γ and TNF than mice infected with L. major. No correlation between the persistence of parasites and IL-10 levels and the production of nitric oxide or urea by macrophages was found. We conclude that infection with low doses of L. amazonensis in the dermis changes the course of infection by delaying the appearance of lesions. However, low-dose infection does not change the outcomes of susceptibility and cytokine production described for subcutaneous infection with high numbers of parasites.     

Short-term protection conferred by Leishvacin® against experimental Leishmania amazonensis infection in C57BL/6 mice

To date, there is no vaccine available against human leishmaniasis. Although some vaccination protocols can induce immunity in murine models, they fail to induce protection in humans. The reasons for that remain unclear. The aim of the present study was to characterize the changes in the pattern of the immune response during subcutaneous vaccination with Leishvacin® in mice. We also investigated whether IFN-γ and nitric oxide synthase are indispensable for the protection elicited by the vaccine. C57BL/6 WT vaccinated mice showed smaller lesions and fewer numbers of parasites in footpads until 8 weeks post-infection. Up to this time, they produced higher levels of IFN-γ, IL-2, IL-4, IL-17A and IL-10 and higher specific antibody response than control non-vaccinated mice. Moreover, we showed that IFN-γ, most likely by induction of iNOS expression, is essential for immunity. However, after 12 weeks of infection, we observed loss of difference in lesion size and parasite burden between the groups. Loss of resistance was associated with the disappearance of differences in cytokine patterns between vaccinated and control mice, but not of antibody response, which remained different until a later time of infection. The reversal of resistance to L. amazonensis could not be explained by upregulation of regulatory cytokines. Our data point to a subversion of the host immune response by L. amazonensis even when a protective response was previously induced.     

Osteopontin-dependent regulation of Th1 and Th17 cytokine responses in Trypanosoma cruzi-infected C57BL/6 mice

Osteopontin (OPN) is a multifunctional protein participating in the regulation of different Th cell lineages and critically involved in the initiation of immune responses to diverse pathogens. Our study goal was to verify whether OPN helps modulate the protective Th1 and Th17 cytokine responses in C57BL/6 mice infected with Trypanosoma cruzi, the etiological agent of Chagas disease. Parasite infection induced OPN release from murine macrophages in vitro and acute Chagas mice displayed enhanced serum levels of this cytokine at the peak of parasitemia. Upon administration of a neutralizing anti-OPN antibody, recently infected mice presented lower Th1 and Th17 responses, increased parasitemia and succumbed earlier and at higher rates to infection than non-immune IgG-receiving controls. The anti-OPN therapy also resulted in reduced circulating levels of IL-12 p70, IFN-γ, IL-17A and specific IgG_2a antibodies. Furthermore, antibody-mediated blockade of OPN activity abrogated the ex vivo production of IL-12 p70, IFN-γ and IL-17A, while promoting IL-10 secretion, by spleen macrophages and CD4⁺ T cells from T. cruzi-infected mice. Th1 and Th17 cytokine release induced by OPN preferentially involved the α_vβ₃ integrin OPN receptor, whereas concomitant down-modulation of IL-10 production would mostly depend on OPN interaction with CD44. Our findings suggest that, in resistant C57BL/6 mice, elicitation of protective Th1 and Th17 cytokine responses to T. cruzi infection is likely to be regulated by endogenous OPN.     

Efficacy of the vaccination of C57BL/6 mice against infection with different species of Leishmania

Antigens were isolated from lysates of promastigotes of Leishmania infantum by electro-elution from polyacrylamide gels. Antigens with respective molecular weights for F2 = 94-67 kd; F5 = 30-20 kd and F6 below 20 kd, were injected intravenously in C 57 BL/6 mice. The immune sera were studied by indirect immunofluorescence; an in vivo test showed their inhibitory effect on the life cycle of several Leishmania species from the Old and the New world. Furthermore, mice immunized with F2, F5 or F6 were protected against an infection by Leishmania major. These results demonstrate that vaccination is efficient in mice differing genetically for either susceptibility (BALB/c) or partial resistance (C 57 BL/6) to Leishmania infections. Recently, we reported that a single monoclonal antibody raised against Leishmania infantum can prevent the development of Leishmania major and Leishmania mexicana amazonensis. Indeed, BALB/c mice injected subcutaneously with promastigotes pre-treated with this monoclonal antibody, did not present any cutaneous lesions over a period of 3 months. Using a mouse in vivo model--intraperitoneal injection of TG 180 mouse sarcoma cells along with monoclonal antibody pre-treated promastigotes--such an antibody-mediated inhibition was also observed against Old and New World Leishmania species. Protective monoclonal antibodies recognized by immunoblotting technique three antigenic fractions (40, 70 and 113 kd) common to several Leishmania species. Antigenic preparations from Leishmania infantum extracts were isolated by electro-elution from polyacrylamide gels.(ABSTRACT TRUNCATED AT 250 WORDS)     

Coxiella burnetii infection in C57BL/6 mice aged 1 or 14 months

The objective of this study was to investigate the effects of age on infection with Coxiella burnetii, the agent of Q fever. Bacterial burden and granuloma number were increased in the spleens of 14-month-old as compared with 1-month-old mice. This increase was not the result of an anti-inflammatory macrophage response, because inflammatory and anti-inflammatory cytokines were induced in macrophages from young mice but were repressed in mature mice. In addition, macrophage microbicidal competence was similar in mature and young mice. These results suggest the importance of individual host factors in the pathophysiology of an infectious disease such as Q fever.     

Dynamics of Th17 cells and their role in Schistosoma japonicum infection in C57BL/6 mice

Background

The current knowledge of immunological responses to schistosomiasis, a major tropical helminthic disease, is insufficient, and a better understanding of these responses would support vaccine development or therapies to control granuloma-associated immunopathology. CD4⁺ T cells play critical roles in both host immune responses against parasitic infection and immunopathology in schistosomiasis. The induction of T helper (Th)1, Th2 and T regulatory (Treg) cells and their roles in schistosome infections are well-illustrated. However, little in vivo data are available on the dynamics of Th17 cells, another important CD4⁺ T cell subset, after Schistosoma japonicum infection or whether these cells and their defining IL-17 cytokine mediate host protective responses early in infection.

Methodology

Levels of Th17 and the other three CD4⁺ T cell subpopulations and the cytokines related to induction or repression of Th17 cell generation in different stages of S. japonicum infection were observed. Contrary to reported in vitro studies, our results showed that the Th17 cells were induced along with the Th1, Th2, Treg cells and the IFN-γ and IL-4 cytokines in S. japonicum infected mice. The results also suggested that S. japonicum egg antigens but not adult worm antigens preferentially induced Th17 cell generation. Furthermore, decreasing IL-17 with a neutralizing anti-IL-17 monoclonal antibody (mAb) increased schistosome-specific antibody levels and partial protection against S. japonicum infection in mice.

Conclusions

Our study is the first to report the dynamics of Th17 cells during S. japonicum infection and indicate that Th17 cell differentiation results from the integrated impact of inducing and suppressive factors promoted by the parasite. Importantly, our findings suggest that lower IL-17 levels may result in favorable host protective responses. This study significantly contributes to the understanding of immunity to schistosomiasis and may aid in developing interventions to protect hosts from infection or restrain immunopathology.     

IL-10 and TGF-beta control the establishment of persistent and transmissible infections produced by Leishmania tropica in C57BL/6 mice

Leishmania tropica is the causative agent of Old World anthroponotic cutaneous leishmaniasis, which is characterized by lesions that take an extended period of time to heal, often resulting in disfiguring scars, and are more refractory to treatment than leishmaniasis caused by Leishmania major. Immunologic studies involving experimental animal models of L. tropica infection are virtually nonexistent. In the current study, infectious-stage L. tropica were used to establish dermal infections in C57BL/6 and BALB/c mice. In both strains, the lesions were slow to develop and showed minimal pathology. They nonetheless contained a stable number of between 10(4) and 10(5) parasites for over 1 year, which were efficiently picked up by a natural sand fly vector, Phlebotomus sergenti. Control of parasite growth depended on the development of a Th1 response, as C57BL/6 mice genetically deficient in Th1 cytokines and BALB/c mice treated with Abs to IFN-gamma harbored significantly more parasites. By contrast, IL-10-deficient mice harbored significantly fewer parasites throughout the infection. To further study the immunologic mechanisms that may prevent efficient clearance of the parasites, IL-10 and TGF-beta signaling were abrogated during the chronic phase of infection in wild-type C57BL/6 mice. Distinct from chronic L. major infection, IL-10 blockade alone had no effect on L. tropica, but required simultaneous treatment with anti-TGF-beta Abs to promote efficient parasite clearance from the infection site. Thus, chronic infection with L. tropica appears to be established via multiple suppressive factors, which together maintain the host as a long-term reservoir of infection for vector sand flies.     

Embryonic stem cells derived from C57BL/6J and C57BL/6N mice

Mouse embryonic stem (ES) cells with the C57BL/6 genetic background allow the generation of knockout mice without the need to backcross to C57BL/6. However, C57BL/6 ES cells whose pluripotency after homologous recombination has been confirmed are not yet available from public cell banks. To facilitate the use of ES cells derived from C57BL/6 sublines in both biologic and medical research, we demonstrated that the use of knockout serum replacement as a medium supplement and 8-cell blastomeres as recipient embryos allowed establishment of ES cells and production of germline chimeric mice, respectively. Under effective conditions, a large number of ES cell lines were established from C57BL/6J and C57BL/6N blastocysts. The majority of ES cells in many cell lines obtained from both strains showed a normal chromosome number. Germline chimeric mice were generated from C57BL/6J and C57BL/6N ES cells. Finally, the ES cell line B6J-S1UTR, derived from C57BL/6J, was used for successful production of gene knockout mice. C57BL/6J ES (B6J-S1UTR and B6J-23UTR) and C57BL/6N ES (B6N-22UTR) cells are available from the cell bank of the BioResource Center at RIKEN Tsukuba Institute (http://www.brc.riken.jp/lab/cell/english/).     

Differences in anxiety-related behavior between apolipoprotein E-deficient C57BL/6 and wild type C57BL/6 mice

The influence of ApoE gene deletion on the anxiety state has not been previously investigated. The elevated plus maze was used in this study to determine differences in anxiety-related behavior between apoE-deficient and wild type C57BL/6 mice. The apoE-deficient mice demonstrated less anxiety on the elevated plus maze by spending more time in the open arms of the elevated plus maze compared to wild type mice (p<0.001). Additionally, female apoE-deficient mice visited the open arm of the maze more often than their apoE-deficient male counterpart (p<0.05). The anxiety state and/or sex are possible variables to be considered when designing physiological and/or behavioral studies involving mice that are apoE-deficient.     

Optimization of topical therapy for Leishmania major localized cutaneous leishmaniasis using a reliable C57BL/6 Model

Background

Because topical therapy is easy and usually painless, it is an attractive first-line option for the treatment of localized cutaneous leishmaniasis (LCL). Promising ointments are in the final stages of development. One main objective was to help optimize the treatment modalities of human LCL with WR279396, a topical formulation of aminoglycosides that was recently proven to be efficient and safe for use in humans.

Methodology/Principal Findings

C57BL/6 mice were inoculated in the ear with luciferase transgenic L. major and then treated with WR279396. The treatment period spanned lesion onset, and the evolution of clinical signs and bioluminescent parasite loads could be followed for several months without killing the mice. As judged by clinical healing and a 1.5-3 log parasite load decrease in less than 2 weeks, the 94% efficacy of 10 daily applications of WR279396 in mice was very similar to what had been previously observed in clinical trials. When WR279396 was applied with an occlusive dressing, parasitological and clinical efficacy was significantly increased and no rebound of parasite load was observed. In addition, 5 applications under occlusion were more efficient when done every other day for 10 days than daily for 5 days, showing that length of therapy is a more important determinant of treatment efficacy than the total dose topically applied.

Conclusions/Significance

Occlusion has a significant adjuvant effect on aminoglycoside ointment therapy of experimental cutaneaous leishmaniasis (CL), a concept that might apply to other antileishmanial or antimicrobial ointments. Generated in a laboratory mouse-based model that closely mimics the course of LCL in humans, our results support a schedule based on discontinuous applications for a few weeks rather than several daily applications for a few days.     

Flp recombinase transgenic mice of C57BL/6 strain for conditional gene targeting

We constructed an expression vector of Flp recombinase modified by adding a nuclear localization signal. Injection of the expression vector into fertilized eggs of the C57BL/6 strain yielded transgenic mouse lines expressing the Flp recombinase transgene in the testis. We crossed the transgenic mice to reporter mice carrying the neomycin phosphotransferase gene flanked by target sites of Flp recombinase. Examination of the deletion of the neomycin phosphotransferase gene in the progeny showed that Flp-mediated recombination took place efficiently in vivo in FLP66 transgenic mouse line. These results suggest that the Flp recombinase system is effective in mice and in combination with the Cre recombinase system extends the potentials of gene manipulation in mice. One of the useful applications of FLP66 transgenic mouse line is the removal of marker genes from mice manipulated for the conditional gene targeting with the Cre/loxP system in the pure C57BL/6 genetic background.     

Immune response of (C57BL/6xA/Sn)F1 mice in mycoplasm-virus infection

Mixed Rauscher leukemia virus (RLV) and M. arthritidis infection of (C57BL/6xA/Sn)f1 mice-hybrids, highly resistant to RLV, was accompanied by a progressive inhibition of rosette-forming cells (RFC) and plaque-forming cells (PFC), resulting in the induction of malignant erythroblastosis identical by cytology to Rauscher leukemia. The mice-hybrids infected with A. laidlawii and RLV developed significant splenomegaly on the 21st day of the infection, and their immune response was almost entirely suppressed, but both RFC and PFC populations as well as the spleen weight returned to the initial level by the 62d day the infection. A possible role of mycoplasm in the induction and development of Rauscher leukemia is discussed.     

Substrains matter in phenotyping of C57BL/6 mice

The inbred mouse strain C57BL/6 has been widely used as a background strain for spontaneous and induced mutations. Developed in the 1930s, the C57BL/6 strain diverged into two major groups in the 1950s, namely, C57BL/6J and C57BL/6N, and more than 20 substrains have been established from them worldwide. We previously reported genetic differences among C57BL/6 substrains in 2009 and 2015. Since then, dozens of reports have been published on phenotypic differences in behavioral, neurological, cardiovascular, and metabolic traits. Substrains need to be chosen according to the purpose of the study because phenotypic differences might affect the experimental results. In this paper, we review recent reports of phenotypic and genetic differences among C57BL/6 substrains, focus our attention on the proper use of C57BL/6 and other inbred strains in the era of genome editing, and provide the life science research community wider knowledge about this subject.     

Autoimmune hair loss induced by alloantigen in C57BL/6 mice

Exponentially growing Meth-A cells expressing H-2K(d).D (d) antigen were found to induce alopecia when injected intraperitoneally into normal C57BL/6 mice, which express the H-2K(b).D (b) antigen. However, the capacity to induce alopecia disappeared when Meth-A cells were treated with K252a, which inhibits protein kinases. Histologically, skin in affected areas showed dense mononuclear cell infiltration and a focal foreign-body giant-cell reaction in hair follicles. The subtyping of lymphocytes in peripheral blood demonstrated a significant difference between normal mice and Meth-A cell-injected mice. To further examine the mechanism by which the alloantigen induces alopecia, lymphocytes isolated from the peripheral blood of normal C57BL/6 mice were cultured in medium containing Meth-A cell homogenate, phytohemagglutinin (PHA) and recombinant mouse interleukin-2 (rm IL-2), and intravenously injected into normal C57BL/6 mice. The adoptive transfer of the lymphocytes induced alopecia in a similar way. These findings suggest that the protein kinase-modulated alloantigen induces alopecia by disturbing the immunological homeostasis, and that lymphokine-activated killer cells play an important role in induction of alopecia by cross-reacting with hair follicles.     

Delayed matching-to-position performance in C57BL/6N mice

Delayed matching-to-sample is one of the most frequently employed behavioral tasks for assessing spatial working memory in animals. Although the advantages of the task have been widely acknowledged and it is used in the study of a variety of species, its application to mice has been rare. In the present study, we reported the efficacy of a delayed matching-to-position task in C57BL mice lever-pressing in an operant-conditioning chamber. Each trial started with the press of a back lever, followed by the presentation of either a left or right front lever. When the ratio requirement for presses to the front lever (sample) was met, a delay interval started. Delay interval continued until the mice made the first response after the elapse of the programmed delay interval. This was followed by the presentation of a choice of left or right front levers. The choice of the same front lever as the sample was reinforced, whereas the other was not. The proportion of correct choices showed a delay-dependent decrement. A higher ratio of response requirement to the sample resulted in increased accuracy, but the duration of the intertrial interval had no effect. Preceding trials also influenced response accuracy, indicating proactive interference. Overall, the results replicated the effects of parametric manipulations reported in other species, and thus, our findings validate the efficacy of the task for assessing spatial working memory in laboratory mice.     

CD4(+) T-cells are important in regulating macrophage polarization in C57BL/6 wild-type mice

During activation, macrophages undergo physiological changes affecting their surface protein expression and cytokine production and have been subsequently categorized into M1 (classically-activated) and M2 (alternatively-activated) macrophages. It remains unclear which lymphocyte population provides the immune microenvironment to regulate macrophage polarization. In this study, we establish a functional and phenotypic profile of peritoneal macrophages from C57BL/6 wild-type mice. We also showed that Rag1^−/− and Rag2^−/−γc^−/− mice have similar, exaggerated M1 characteristics in comparison to control mice, suggesting that NK and/or NK-T cells may not be essential in this process. By controlling for environmental factors, we determine that lymphocyte-derived cytokines, rather than inherent properties of macrophages themselves, are crucial for their regulation. Lastly, we report that macrophages from CD4^−/− mice display an M1 profile, suggesting that CD4⁺ T-cells play a dominant role over other lymphocyte populations in providing the cytokine environment for regulating macrophages towards an M2 profile under normal wild-type conditions.