Toxoplasma gondii infection blocks the development of allergic airway inflammation in BALB/c mice

There is a link between increased allergy and a reduction of some infections in western countries. Epidemiological data also show that respiratory allergy is less frequent in people exposed to orofaecal and foodborne microbes such as Toxoplasma gondii. Infection with T. gondii induces a strong cell-mediated immunity with a highly polarized T helper type 1 (Th1) response in early stages of infection. Using a well-known murine model of allergic lung inflammation, we sought to investigate whether T. gondii infection could modulate the susceptibility to develop respiratory allergies. Both acute and chronic infection with T. gondii before allergic sensitization resulted in a diminished allergic inflammation, as shown by a decrease in bronchoalveolar lavage (BAL) eosinophilia, mononuclear and eosinophil cell infiltration around airways and vessels and goblet cell hyperplasia. Low allergen-specific immunoglobulin (Ig)E and IgG1 and high levels of allergen-specific IgG2a serum antibodies were detected. A decreased interleukin (IL)-4 and IL-5 production by lymph node cells was observed, while no antigen-specific interferon-γ increase was detected. Higher levels of the regulatory cytokine IL-10 were found in BAL from infected mice. These results show that both acute and chronic parasite infection substantially blocked development of airway inflammation in adult BALB/c mice. Our results support the hypothesis that T. gondii infection contributes to protection against allergy in humans.     

Different strains of Toxoplasma gondii induce different cytokine responses in CBA/Ca mice

To investigate the role that cytokines may have in the development of toxoplasmic encephalitis (TE), the levels of gamma interferon (IFN-gamma), tumor necrosis factor alpha (TNF-alpha), interleukin-12 (IL-12 ]p40[), IL-10, IL-6, IL-4, and IL-2 in serum were examined in CBA/Ca mice infected with a type II strain (ME49 or FORT) of Toxoplasma gondii. These strains caused severe (ME49) or mild (FORT) TE in CBA/Ca mice. From weeks 1 to 8 of infection, the levels of IL-6, IL-10, IL-12, IFN-gamma, and TNF-alpha in serum were significantly higher in the ME49-infected mice than in the FORT-infected mice, suggesting a role for these cytokines in the severity of TE in CBA/Ca mice. Since the ME49 and FORT strains are of the same type, our results suggest a role for the parasite in the development of severe TE through the increased production of proinflammatory cytokines and indicate that not all type II strains cause TE.     

Vaccination with Toxoplasma gondii SAG-1 protein is protective against congenital toxoplasmosis in BALB/c mice but not in CBA/J mice

We evaluated the effect of vaccination with the SAG1 protein of Toxoplasma gondii against congenital toxoplasmosis in mice with different genetic backgrounds. In BALB/c mice (H-2(d)), vaccination reduced the number of infected fetuses by 50% and was associated with a mixed type 1 and type 2 immunity. In CBA/J mice (H-2(k)), vaccination increased the number of infected fetuses by 50% and was associated with a predominant type 2 response. Our results indicate that the effect of vaccination with SAG1 is controlled by the genetic background of the mouse.     

BALB/c mice resistant to Toxoplasma gondii infection proved to be highly susceptible when previously infected with Myocoptes musculinus fur mites

The immune response induced by Toxoplasma gondii is characterized by Th1 immune mechanisms. We previously demonstrated that C57BL/6 mice infested with Myocoptes musculinus and infected with T. gondii by intraperitoneal route undergo accelerated mortality according to Th2 immune mechanisms induced by the acarian. To evaluate whether infection with M. musculinus influences T. gondii-induced Th1 response in a resistant mouse lineage, BALB/c, which develops latent chronic toxoplasmosis in a way similar to that observed in immunocompetent humans, this study was done. The animals were infected with T. gondii ME-49 strain 1 month after M. musculinus infestation, being the survival and the immune response monitored. The double-infected displayed higher mortality rate if compared with the mono-infected mice. In addition, infection with M. musculinus changed the T. gondii-specific immune response, converting BALB/c host to a susceptible phenotype. Spleen cells had increased the levels of IL-4 in double-infected mice. This alteration was associated with severe pneumonia, encephalitis and wasting condition. In addition, a higher tissue parasitism was observed in double-infected animals. It can be concluded that infection with these two contrasting parasites, M. musculinus and T. gondii, may convert an immunocompetent host into a susceptible one, and such a host will develop severe toxoplasmosis.     

CR3-dependent resistance to acute Toxoplasma gondii infection in mice.

Studies were performed to determine whether resistance to acute Toxoplasma gondii infection in mice depends on a mechanism involving CR3, the type 3 complement receptor. Nineteen of 22 mice (86%) given multiple injections of the anti-CR3 monoclonal antibody, 5C6, prior to and after intraperitoneal inoculation of cysts of the ordinarily mildly virulent ME49 strain of T. gondii died within 8 to 12 days, whereas control antibody-treated mice survived. All (five of five) anti-CR3-treated BALB/c mice infected via the natural peroral route died within 8 days of infection. Flow cytometric analysis of cells recovered from peritoneal lavages of anti-CR3-treated T. gondii-infected mice revealed that the percentage of Thy-1+ CD4- CD8- cells was reduced to about 50% of that of control antibody-treated mice and to about 20% of the number of such cells in controls. The numbers of macrophages, polymorphonuclear leukocytes, and lymphocytes recovered from the peritoneal cavities of T. gondii-infected mice were all reduced in anti-CR3-treated mice to about 40% of those of controls. In addition, anti-CR3-treated mice had less than 25% of the induced NK cell activity of the controls, and gamma interferon was reduced to undetectable levels. Thus, the rapid death of anti-CR3-treated mice was probably caused by impaired preimmune defenses. Histological examination of anti-CR3-treated T. gondii-infected mice revealed extensive liver pathology compared with that of infected mice given a control antibody or uninfected mice given anti-CR3. The inflammation, degeneration, and necrosis in most of the anti-CR3-treated mice were severe enough to account for the observed mortalities.     

IL-4 depletion enhances host resistance and passive IgA protection against tuberculosis infection in BALB/c mice

The influence of Th2 cytokines in tuberculosis has been a matter of dispute. Here we report that IL-4 has a profound regulatory effect on the infection of BALB/c mice with Mycobacterium tuberculosis. Depletion of IL-4 with a neutralizing mAb caused only evanescent reduction of lung infection, but when combined with i.n. inoculations of IgA anti-mycobacterial alpha-crystallin mAb and mouse rIFN-gamma, we observed a 40-fold reduction of the bacterial counts in the lungs at 3 wks following i.n. infection (p<0.001). In genetically deficient IL-4-/- BALB/c mice, infection in both lung and spleen was substantially reduced for up to 8 wks without further treatment. Reconstitution of IL-4-/- mice with rIL-4 increased bacterial counts to wild-type levels and made the mice refractory to protection by IgA/IFN-gamma. Analysis of the lungs showed increased granulomatous infiltration and proinflammatory mediators in anti-IL-4/IgA/IFN-gamma-treated and infected mice. We conclude that the action of IL-4 in tuberculosis is targeted at macrophages and that it may include an antagonistic effect on their IgA/IFN-gamma-induced activation and nitric oxide production. The described novel immunotherapy, combining treatments with anti-IL-4, IgA antibody and IFN-gamma, has potential for translation toward the passive immunoprophylaxis of tuberculosis.     

Senescent BALB/c mice are able to develop resistance to Leishmania major infection

Aging has been associated with a decline in immunocompetence and resistance to infections, partially due to dysregulated NO production by macrophages and deficits in mounting Th2 cell responses. We wondered if these alterations would reverse the immune response in experimental leishmaniasis. Bone-marrow-derived macrophages from 2- and 18-month-old (senescent) C57BL/6 or BALB/c mice showed no marked difference in leishmanicidal functions. In vivo infections of resistant C57BL/6 mice with Leishmania major revealed no difference between senescent and young mice. However, among susceptible BALB/c mice, senescent animals showed less foot-pad swelling than young mice, and 40 to 60% of them even showed healing of ulcers, reduced parasite dissemination, and a Th1 cell response. These changes were associated with a spontaneous release of interleukin-12 (IL-12) by macrophages from aged but not from young mice. Since exogenous microbial stimulation can influence immune responses during aging, we also infected senescent mice who were raised under specific-pathogen-free (SPF) conditions. They showed neither resistance nor a Th1 response, but their macrophages still spontaneously released IL-12. A microbiological analysis showed that conventionally kept mice, but not SPF mice, had experienced infection with murine hepatitis virus (MHV), an infection associated with a Th1-like response. We conclude that for the reversal of the immune response, senescence is the premier requirement but needs to be completed by another mandatory event such as microbial stimulation. One of the age-related, but not environment-related, factors is the spontaneous release of IL-12 by macrophages, while confrontation with MHV presents an environment-related difference, with both having the potential to support a Th1 response.     

Toll-like receptors and their role in host resistance to Toxoplasma gondii

Toxoplasma gondii and other apicomplexan parasites are widely distributed obligate intracellular protozoa. A critical host mediator produced in response to T. gondii infection is IL-12. This cytokine is synthesized by dendritic cells, macrophages and neutrophils and plays a pivotal role in the production of IFN-gamma, which in turn activates anti-microbial effector cells. In the past several years, many of the receptors and signaling pathways that link pathogen detection to induction of IL-12 have been identified and characterized. Among these receptors the Toll-like receptor (TLR) family can recognize all classes of pathogens and induce different types of immune responses. In the following review, I summarize the evidence for specific TLR function in host resistance to T. gondii.     

Effect of cocaine on the immune response and host resistance in BALB/c mice

This study focuses on the effect of varying regimens of cocaine administration on three parameters of the immune response: antibody production, resistance to infection by Streptococcus pneumoniae following immunization, and resistance to tumors. The effect of cocaine on antibody production of female and male BALB/c mice was investigated to both a T-independent (pneumococcal polysaccharide type III [SSS-III]) and a T-dependent antigen (the 2,4-dinitrophenyl ligand [DNP]). It was found that high doses of cocaine injected 3 times/day prior to SSS-III resulted in a small rise in antibody levels in male mice. Low doses given for 4 days prior to or subsequent to SSS-III injection had no effect on the antibody response nor on the susceptibility to infection by live S. pneumoniae. High dosages of cocaine administered 3-5 times/day had no effect on the anti-DNP immune response of male mice but resulted in an almost 2-fold increase of anti-DNP plaque-forming cells in female mice.     

Induction and regulation of IL-12-dependent host resistance to Toxoplasma gondii

Resistance to the intracellular protozoan parasite Toxoplasma gondii is initiated by the induction of interleukin-12 (IL-12), which stimulates interferon (IFN)-gamma synthesis by natural killer (NK) cells and T lymphocytes. This review summarizes the work of our laboratory on the mechanisms by which the parasite triggers IL-12 synthesis, and how this response is regulated to avoid the lethal effects of excessive tissue inflammation. In addition, we present an overview of our studies investigating the mechanisms by which the IFN-gamma produced as a consequence of IL-12 stimulation controls intracellular replication of the parasite in host cells.     

Induction and regulation of IL-12-dependent host resistance to Toxoplasma gondii

Resistance to the intracellular protozoan parasite Toxoplasma gondii is initiated by the induction of interleukin-12 (IL-12), which stimulates interferon (IFN)-γ synthesis by natural killer (NK) cells and T lymphocytes. This review summarizes the work of our laboratory on the mechanisms by which the parasite triggers IL-12 synthesis, and how this response is regulated to avoid the lethal effects of excessive tissue inflammation. In addition, we present an overview of our studies investigating the mechanisms by which the IFN-γ produced as a consequence of IL-12 stimulation controls intracellular replication of the parasite in host cells.     

Migratory activation of primary cortical microglia upon infection with Toxoplasma gondii

Disseminated toxoplasmosis in the central nervous system (CNS) is often accompanied by a lethal outcome. Studies with murine models of infection have focused on the role of systemic immunity in control of toxoplasmic encephalitis, while knowledge remains limited on the contributions of resident cells with immune functions in the CNS. In this study, the role of glial cells was addressed in the setting of recrudescent Toxoplasma infection in mice. Activated astrocytes and microglia were observed in the close vicinity of foci with replicating parasites in situ in the brain parenchyma. Toxoplasma gondii tachyzoites were allowed to infect primary microglia and astrocytes in vitro. Microglia were permissive to parasite replication, and infected microglia readily transmigrated across transwell membranes and cell monolayers. Thus, infected microglia, but not astrocytes, exhibited a hypermotility phenotype reminiscent of that recently described for infected dendritic cells. In contrast to gamma interferon-activated microglia, Toxoplasma-infected microglia did not upregulate major histocompatibility complex (MHC) class II molecules and the costimulatory molecule CD86. Yet Toxoplasma-infected microglia and astrocytes exhibited increased sensitivity to T cell-mediated killing, leading to rapid parasite transfer to effector T cells in vitro. We hypothesize that glial cells and T cells, besides their role in triggering antiparasite immunity, may also act as "Trojan horses," paradoxically facilitating dissemination of Toxoplasma within the CNS. To our knowledge, this constitutes the first report of migratory activation of a resident CNS cell by an intracellular parasite.     

Hematopoiesis during acute Toxoplasma gondii infection in mice

We studied hematopoiesis in bone marrow and blood of CBA mice following infection with Toxoplasma gondii. Our data showed that acute infection with the virulent RH strain was associated with leucopenia, thrombocytopenia and bone marrow hypoplasia while, in spite of the infection-induced damage of the granulocyte cell lineage, in bone marrow stimulated production of granulocytes was revealed. In peripheral blood, T. gondii infection caused a significant decrease in the total number of white blood cells, reticulocytes and platelets. However, the relative proportion of granulocytes and lymphocytes was changed in favor of granulocytes, as compared to pre-infection levels. The functional activity of granulocytes was also increased. The bone marrow alterations were characterized by a decrease in the total number of nucleated cells due to the reduced numbers in all cell compartments of erythroid and megakaryocytic lineage, as well as in the number of mature granulocytes and lymphocytes. In contrast, femoral granulocytic proliferative compartments, colony forming unite granulocyte-macrophage (CFU-GM) and morphologically recognizable proliferative granulocytes (PG), exhibited stimulated granulopoiesis, while the number of mature monocytes was close to the control value. In summary, we have shown that acute T. gondii infection results in profound alterations of the hematopoietic system that markedly contribute to the clinical onset of the disease and the, ultimately lethal, outcome.     

Role of beta interferon in resistance to Toxoplasma gondii infection.

The role of recombinant murine beta interferon (rMuIFN-beta) and recombinant human IFN-beta (rHuIFN-beta) in resistance to Toxoplasma gondii was examined. rMuIFN-beta protected mice against a lethal infection with the parasite. The protective effect appeared to depend on the concomitant release of gamma interferon. rMuIFN-beta did not activate murine peritoneal macrophages to inhibit or kill T. gondii whether used alone or in combination with lipopolysaccharide (LPS). rHuIFN-beta did not activate human monocyte-derived macrophages to inhibit or kill T. gondii when 5-day-old monocyte-derived macrophages were used. In contrast, significant killing of T. gondii was noted when 10-day-old monocyte-derived macrophages were used. The addition of LPS enhanced this effect. These results revealed a role for IFN-beta in the mechanisms of defense against T. gondii and suggest its potential use in the treatment of toxoplasmosis in humans.     

Adjuvant treatment increases the resistance to Mycobacterium avium infection of mycobacteria-susceptible BALB/c mice.

Systemic lupus erythematosus (SLE)-like anti-IgG Fab autoantibodies (autoAb) were induced in rabbits by immunization with either human, mouse or rabbit anti-DNA Ab. In direct-binding radioimmunoassay (RIA), affinity-purified anti-normal rabbit (NR) Fab autoAb cross-reacted with normal mouse (NM) Fab, ssDNA (but not dsDNA), poly(dA,dT), and RNA polymerase I (RPI). Affinity-purified anti-NM IgG Ab isolated from the same antisera cross-reacted with NR Fab, ssDNA and RPI. In inhibition RIA, soluble NR Fab inhibited anti-NR Fab binding to NR Fab and ssDNA, but enhanced binding to RPI. In contrast, ssDNA or RPI inhibitors had no effect upon autoAb binding to NR Fab. Anti-DNA, anti-RPI and anti-RPI 190 kD subunit autoAb, induced by immunization with lupus mouse anti-DNA Ab, also reacted with NM Fab, but were idiotypically specific for lupus mouse anti-DNA Fab. Further, rabbit anti-DNA and anti-RPI IgG autoAb, induced by immunization with rabbit anti-DNA IgG, were each idiotypically specific for homologous and autologous rabbit anti-ssDNA Fab. Together, these data provide evidence that anti-DNA, anti-RPI and anti-Fab autoAb are linked in a complex, multiple-specific and perhaps regulatory, immune response idiotype network in SLE.     

Protective immunity induced by a DNA vaccine-encoding Toxoplasma gondii microneme protein 11 against acute toxoplasmosis in BALB/c mice

Toxoplasma gondii is one of the most prevalent intracellular parasites and is threatening the health of both humans and animals, therefore causing incalculable economic losses worldwide. Vaccination is thought to be an efficient way of controlling toxoplasmosis. T. gondii microneme protein 11 (MIC11) is a soluble microneme protein which is presumably considered facilitating the early stage of cell invasion. To evaluate the protective efficacy of T. gondii MIC11, in the present study, a new DNA vaccine-encoding the α-chain of T. gondii MIC11 was constructed using the pcDNA3.1 vector. Expression of MIC11 from this vector was confirmed by indirect immunofluorescence assay following transfection into baby hamster kidney (BHK) cells. Intramuscular immunization of BALB/c mice with pcDNA/MIC11 was carried out to evaluate the immune responses by serum antibodies titers, lymphoproliferation assay, and cytokines assay. The protective efficacy was evaluated by survival rate in mice after challenging with highly virulent strain of T. gondii. The results demonstrated that this vaccination elicited significant humoral responses and T. gondii lysate antigen (TLA)-stimulated lymphoproliferation (p?<?0.05). Compared to controls, the pcDNA/MIC11 immunized mice had high production of IFN-γ, IL-12, and IL-2 (p?<?0.05), but not IL-4 (p?>?0.05), indicating that a predominant Th1 type response was developed. The vaccination also increased the survival rate of immunized mice when they were challenged with a lethal dose of tachyzoites of T. gondii RH strain. These data suggest that T. gondii MIC11 is a reasonable vaccine candidate deserving further studies, and pcDNA/MIC11 is a potential strategy for the control of toxoplasmosis.     

Pathogenesis of Yersinia pestis infection in BALB/c mice: effects on host macrophages and neutrophils

The pathogenesis of infection with Yersinia pestis, the causative agent of plague, was examined following subcutaneous infection of BALB/c mice with a fully virulent strain expressing green fluorescent protein. Plate culturing, flow cytometry, and laser confocal microscopy of spleen homogenates throughout infection revealed three discernible stages of infection. The early phase was characterized by the presence of a small number of intracellular bacteria mostly within CD11b+ macrophages and Ly-6G+ neutrophils. These bacteria were not viable, as determined by plate culturing of spleen homogenates, until day 2 postinfection. Between days 2 and 4 postinfection, a plateau phase was observed, with bacterial burdens of 10(3) to 10(4) CFU per spleen. Flow cytometric analysis revealed that there was even distribution of Y. pestis within both CD11b+ macrophage and Ly-6G+ neutrophil populations on day 2 postinfection. However, from day 3 postinfection onward, intracellular bacteria were observed exclusively within splenic CD11b+ macrophages. The late phase of infection, between days 4 and 5 postinfection, was characterized by a rapid increase in bacterial numbers, as well as escape of bacteria into the extracellular compartment. Annexin V staining of spleens indicated that a large proportion of splenic neutrophils underwent rapid apoptosis on days 1 and 2 postinfection. Fewer macrophages underwent apoptosis during the same period. Our data suggest that during the early stages of Y. pestis infection, splenic neutrophils are responsible for limiting the growth of Y. pestis and that splenic macrophages provide safe intracellular shelters within which Y. pestis is able to grow and escape during the later stages of infection. This macrophage compliance can be overcome in vitro by stimulation with a combination of gamma interferon and tumor necrosis factor alpha.     

BALB/c和SCID小鼠人偏肺病毒感染特点的比较研究

目的 比较研究人偏肺病毒(hMPV)在BALB/c小鼠和SCID小鼠肺内复制动力学和肺病理特点.方法 GFP-rhMPV滴鼻感染BALB/c小鼠和SCID小鼠,于感染后3、5、7、9、14d处死小鼠并无菌获取心、肝、脾、肺、肾和脑用于病毒分离和病理检查,空斑形成法检测病毒滴度,RT-PCR和real-time PCR法检测hMPV mRNA表达.结果 GFP-rhMPV滴鼻感染BALB/c小鼠和SCID小鼠后第5天肺组织均分离到病毒.感染GFP-rhMPV的BALB/c和SCID小鼠在感染后第5天肺组织病毒滴度均达峰值,分别为(5.25±1.69)×104 PFU/g和(5.83±1.21)×105 PFU/g.SCID小鼠在感染后第14天肺组织内病毒滴度仍可达(4.25±1.04) ×101 PFU/g,此时BALB/c鼠肺内已不能分离到病毒,但可检测到GFP-rhMPV F蛋白mRNA表达.感染后第5天所有小鼠的心、肝、脾、肾和脑组织内均不能分离到病毒,也无法检测到hMPV F蛋白mRNA表达.肺组织病理改变在感染后第5天最明显,为典型的间质性肺炎改变,BALB/c小鼠组肺组织病理评分略低于SCID小鼠组,差异无统计学意义.结论 GFP-rhMPV滴鼻感染后只能在小鼠肺内复制.同BAL B/c小鼠相比,SCID小鼠感染GFP-rhMPV后肺内病毒滴度高,复制时间久,但病理损伤无明显差异.     

Nitric oxide and HSV vaginal infection in BALB/c mice

Here we study the role of nitric oxide in the vaginal infection of Balb/c mice with herpes simplex virus type 2. Inducible nitric oxide synthase (iNOS) mRNA was detected by RT-PCR in vaginal tissue and inguinal lymph nodes early postinfection. iNOS was also found to be activated in cells recovered from vaginal washings of infected animals. Animals treated with aminoguanidine (AG), an iNOS inhibitor, showed a dose-dependent increase in vaginal pathology after viral infection compared to controls. Viral titers in vaginal washings and vaginas were higher in AG-treated mice. Treated animals presented higher PMN counts in vaginal washings compared to controls. Histopathology studies revealed a profound inflammatory exudate in vaginal tissue of treated animals. Finally, RT-PCR analysis showed increased expression of the chemokines MIP-2 and RANTES in vaginal tissue and inguinal lymph nodes of these animals.     

Mycobacterium avium infection in BALB/c and SCID mice.

BALB/c and severe combined immunodeficient (SCID) mice were inoculated intraperitoneally with Mycobacterium avium and the numbers of cfu were monitored for 70 days in spleen, liver, lung, kidney, brain and peritoneum. While BALB/c mice formed typical granulomas and controlled bacterial growth in organs, a delay in development of lesions and a modest containment of infection were observed in SCID mice. In the spleen of BALB/c mice, in which bacterial growth was contained, macrophages (Mo) and natural killer (NK) cell numbers increased > or = 4.2 times and T- and B-cell numbers increased > or = 1.8 times after 42 days of infection; conversely, a low recruitment of mononuclear cells was observed in the spleen of SCID mice, where M. avium proliferated efficiently. Unlike visceral organs, a pronounced decrease in the number of cfu was observed in the peritoneum of BALB/c mice, concomitantly with a > or = 31.7-fold increase in Mo and NK cells and a > or = 9.1-fold increase in T and B cells. In the peritoneum of SCID mice only a bacteriostatic effect was observed despite a > or = 56.7-fold increase in Mo and NK cells and a > or = 22.3-fold increase in T and B cells. These results suggest that while an intact immune response can efficiently control M. avium infection in the spleen and peritoneum of BALB/c mice, cells of the innate immune system such as Mo and NK cells play a role in the containment of bacterial growth in the peritoneum, but not spleen, of SCID mice.