Schistosoma mansoni Coinfection Attenuates Murine Toxoplasma gondii-Induced Crohn's-Like Ileitis by Preserving the Epithelial Barrier and Downregulating the Inflammatory Response.

Background and aims: Mice orally infected with T. gondii develop Crohn's disease (CD)-like enteritis associated with severe mucosal damage and a systemic inflammatory response, resulting in high morbidity and mortality. Previously, helminthic infections have shown therapeutic potential in experimental colitis. However, the role of S. mansoni in T. gondii-induced CD-like enteritis has not been elucidated. Our study investigated the mechanisms underlying T. gondii-induced ileitis and the potential therapeutic effect of S. mansoni coinfection. Methods: C57BL/6 mice were infected by subcutaneous injection of cercariae of the BH strain of S. mansoni, and 7-9 weeks later, they were orally infected with cysts of the ME49 strain of T. gondii. After euthanasia, the ileum was removed for histopathological analysis; staining for goblet cells; immunohistochemistry characterizing mononuclear cells, lysozyme expression, apoptotic cells, and intracellular pathway activation; and measuring gene expression levels by real-time PCR. Cytokine concentrations were measured in the serial serum samples and culture supernatants of the ileal explants, in addition to myeloperoxidase (MPO) activity. Results:T. gondii-monoinfected mice presented dense inflammatory cell infiltrates and ulcerations in the terminal ileum, with abundant cell extrusion, apoptotic bodies, and necrosis; these effects were absent in S. mansoni-infected or coinfected animals. Coinfection preserved goblet cells and Paneth cells, remarkably depleted in T. gondii-infected mice. Densities of CD4- and CD11b-positive cells were increased in T. gondii- compared to S. mansoni-infected mice and controls. MPO was significantly increased among T. gondii-mice, while attenuated in coinfected animals. In T. gondii-infected mice, the culture supernatants of the explants showed increased concentrations of TNF-alpha, IFN-gamma, and IL-17, and the ileal tissue revealed increased expression of the mRNA transcripts for IL-1 beta, NOS2, HMOX1, MMP3, and MMP9 and activation of NF-kappa B and p38 MAPK signaling, all of which were counterregulated by S. mansoni coinfection. Conclusion:S. mansoni coinfection attenuates T. gondii-induced ileitis by preserving mucosal integrity and downregulating the local inflammatory response based on the activation of NF-kappa B and MAPK. The protective function of prior S. mansoni infection suggests the involvement of innate immune mechanisms and supports a conceptually new approach to the treatment of chronic inflammatory diseases, including CD.

Evaluation of immune responses in mice after DNA immunization with putative Toxoplasma gondii calcium-dependent protein kinase 5.

Toxoplasma gondii can cause serious public health problems and economic losses worldwide. Calcium-dependent protein kinases (CDPKs) are key mediators of T. gondii signaling pathways and are implicated as important virulence factors. In the present study, we cloned a novel T. gondii CDPK gene, named TgCDPK5, and constructed the eukaryotic expression vector pVAX-CDPK5. Then, we evaluated the immune protection induced by pVAX-CDPK5 in Kunming mice. After injection of pVAX-CDPK5 intramuscularly, immune responses, determined with lymphoproliferative assays and cytokine and antibody measurements, were monitored, and mouse survival times and brain cyst formation were evaluated following challenges with the T. gondii RH strain (genotype I) and the PRU strain (genotype II). pVAX-CDPK5 effectively induced immune responses with increased specific antibodies, a predominance of IgG2a production, and a strong lymphocyte proliferative response. The levels of gamma interferon (IFN-γ), interleukin 2 (IL-2), and IL-12(p70) and the percentages of CD3(+) CD4(+) and CD3(+) CD8(+) cells in mice vaccinated with pVAX-CDPK5 were significantly increased. However, IL-4 and IL-10 were not produced in the vaccinated mice. These results demonstrate that pVAX-CDPK5 can elicit strong humoral and cellular Th1 immune responses. The survival time of immunized mice challenged with the T. gondii RH strain (8.67 ± 4.34 days) was slightly, but not significantly, longer than that in the control groups within 7 days (P > 0.05). The numbers of brain cysts in the mice in the pVAX-CDPK5 group were reduced by ∼40% compared with those in the control groups (P < 0.05), which provides a foundation for the further development of effective subunit vaccines against T. gondii.

Measurement of IL-10 serum levels in balb/c mice treated with beta-1, 3 polyglucose or sulfadiazine and acutely infected by Toxoplasma gondii

Acute infection by Toxoplasma gondii leads to suppression of cell-mediated immunity, facilitating chronic infection. One of the causes of immunosuppression is Interleukin-10 (IL-10) production. Glucan is used to stimulate phagocytosis. Our objective was to study IL-10 induction in male BALB/c mice with acute T. gondii BTU-2 strain infection, glucan immunostimulation, and sulfadiazine treatment. Animals were distributed into 7 groups: G1: infected with T. gondii; G2: infected with T. gondii and treated with sulfadiazine; G3: infected with T. gondii and immunostimulated with glucan; G4: infected with T. gondii, immunostimulated with glucan, and treated with sulfadiazine; G5: imunostimulated with glucan; G6: treated with saline; and G7: treated with sulfadiazine. IL-10 levels were determined by ELISA; the highest levels were found in G2, G3 and G4, and the lowest in G1 (p<0.001). Groups G1 to G5 and G7 had substantially higher levels than G6 (p<0.001). In this study, the highest IL-10 levels were found in groups treated with glucan

Exacerbated susceptibility to infection-stimulated immunopathology in CD1d-deficient mice.

Mice lacking functional CD1d genes were used to study mechanisms of resistance to the protozoan parasite Toxoplasma gondii. Wild-type (WT) BALB/c mice, CD1d-deficient BALB/c mice, and WT C57BL/6 mice all survived an acute oral infection with a low dose of mildly virulent strain ME49 T. gondii cysts. In contrast, most CD1d-deficient C57BL/6 mice died within 2 wk of infection. Despite having parasite burdens that were only slightly higher than WT mice, CD1d-deficient C57BL/6 mice displayed greater weight loss and intestinal pathology. In C57BL/6 mice, CD4(+) cells can cause intestinal pathology during T. gondii infection. Compared with WT mice, infected CD1d-deficient C57BL/6 mice had higher frequencies and numbers of activated (CD44(high)) CD4(+) cells in mesenteric lymph nodes. Depletion of CD4(+) cells from CD1d-deficient mice reduced weight loss and prolonged survival, demonstrating a functional role for CD4(+) cells in their increased susceptibility to T. gondii infection. CD1d-deficient mice are deficient in Valpha14(+) T cells, a major population of NKT cells. Involvement of these cells in resistance to T. gondii was investigated using gene-targeted Jalpha18-deficient C57BL/6 mice, which are deficient in Valpha14(+) T cells. These mice did not succumb to acute infection, but experienced greater weight loss and more deaths than B6 mice during chronic infection, indicating that Valpha14(+) cells contribute to resistance to T. gondii. The data identify CD4(+) cells as a significant component of the marked susceptibility to T. gondii infection observed in CD1d-deficient C57BL/6 mice, and establish T. gondii as a valuable tool for deciphering CD1d-dependent protective mechanisms.

Azithromycin prophylaxis and treatment of murine toxoplasmosis.

OBJECTIVE: To evaluate the azithromycin effects alone and in combination with other agents in the prophylaxis and treatment of murine toxoplasmosis. METHODS: A total of 280 BALB/c mice were included, and 2 x 103 Toxoplasma organisms of the RH strain Toxoplasma gondii strain ATCC50174 were given intraperitoneally to each mouse. In experiment one, 40 animals were given azithromycin 200 milligram/kilogram/daily for 3 days starting the day of inoculation, 40 mice were control. In experiment 2, the treatment was started 48 hours after inoculation and given daily for 3 days: one group received azithromycin 200 milligram/kilogram/day, the second group received pyrimethamine 25 milligram/kilogram/day, and the sulfadiazine 100 milligram/kilogram/day. The third group was control. In experiment 3, 7 groups of animals received one of the following (1) none, (2) azithromycin 200 milligram/kilogram/day, (3) pyrimethamine 25 milligram/kilogram/day and sulfadiazine 100 milligram/kilogram/day, (4) azithromycin and sulfadiazine, (5) azithromycin and pyrimethamine, (6) azithromycin with sulfadiazine and pyrimethamine, (7) sulfadiazine alone. Treatment was initiated 72 hours after inoculation for 3 days. The study was conducted at the Animal Care Facility of King Saud University, Riyadh, Kingdom of Saudi Arabia. RESULTS: Animals that received azithromycin simultaneously with inoculation survived, and all control animals died. All animals died in groups receiving single drug therapy. Animals treated with azithromycin and sulfadiazine showed a survival rate of 40%, sulfadiazine and pyrimethamine 40%, or azithromycin with sulfadiazine and pyrimethamine 95% (p<0.0001). CONCLUSION: Azithromycin alone was found to be effective in the prophylaxis of murine toxoplasmosis. Combination therapy was effective in the treatment of murine toxoplasmosis.

Effect of administration of a recombinant adenovirus expressing the genes for IFN-gamma and interleukin-12 on acute murine toxoplasmosis.

The effect of recombinant murine interferon-gamma (rMuIFN-gamma) produced from an adenovirus construct on Toxoplasma gondii in tissue culture and on the outcome of a T. gondii infection in mice was determined. Supernatants from AdCMVMuIFN-gamma-infected mouse lung epithelial (MuLE) cells were evaluated for the ability to produce biologically active IFN-gamma by measuring the capacity of the supernatants to activate peritoneal macrophages for killing of T. gondii. The bioactivity of IFN-gamma in supernatants increased with increasing multiplicity of infection (moi). Replication was inhibited 43%, 67%, and 70% by supernatants from MuLE cells infected with AdCMVMuIFN-gamma moi 5, 10, and 50, respectively, (p < 0.01 compared with controls). Bioactivity of IFN-gamma also increased as the length of time after infection increased. T. gondii replication was inhibited 28% and 36%, respectively, by AdCMVMuIFN-gamma-infected MuLE cell supernatants recovered at 24 and 48 h (p < 0.01 compared with control). In vivo administration of AdCMVMuIFN-gamma exhibited 33% mortality by day 9 in mice acutely infected with T. gondii compared with 100% mortality in control mice (p = 0.045). Administration of AdCMVIL-12 reduced mortality to 40% compared with control mice. However, this reduction was not significant (p = 0.08). Overall survival was extended 2 days with AdCMVMuINF-gamma administration and 5 days with AdCMVIL-12. AdCMVMuIFN-gamma in vitro inhibits T. gondii, and in vivo AdCMVMuIFN-gamma and AdCMVIL-12 lead to increased survival in mice.

Acute toxoplasmosis leads to lethal overproduction of Th1 cytokines.

Virulence in Toxoplasma gondii is strongly influenced by the genotype of the parasite. Type I strains uniformly cause rapid death in mice regardless of the host genotype or the challenge dose. In contrast, the outcome of infections with type II strains is highly dependent on the challenge dose and the genotype of the host. To understand the basis of acute virulence in toxoplasmosis, we compared low and high doses of the RH strain (type I) and the ME49/PTG strain (type II) of T. gondii in outbred mice. Differences in virulence were reflected in only modestly different growth rates in vivo, and both strains disseminated widely to different tissues. The key difference in the virulent RH strain was the ability to reach high tissue burdens rapidly following a low dose challenge. Lethal infections caused by type I (RH) or type II (PTG) strain infections were accompanied by extremely elevated levels of Th1 cytokines in the serum, including IFN-gamma, TNF-alpha, IL-12, and IL-18. Extensive liver damage and lymphoid degeneration accompanied the elevated levels of cytokines produced during lethal infection. Increased time of survival following lethal infection with the RH strain was provided by neutralization of IL-18, but not TNF-alpha or IFN-gamma. Nonlethal infections with a low dose of type II PTG strain parasites were characterized by a modest induction of Th1 cytokines that led to control of infection and minimal damage to host tissues. Our findings establish that overstimulation of immune responses that are normally necessary for protection is an important feature of acute toxoplasmosis.

Toxoplasmosis.

Toxoplasmosis in dogs and cats can cause chorioretinitis, anterior uveitis, or both. Ocular lesions are a common manifestation of generalized toxoplasmosis. The prevalence of toxoplasmosis as a cause of idiopathic anterior uveitis in cats is not clear, although there is a significant association between exposure to T. gondii and feline anterior uveitis. The pathogenesis of ocular toxoplasmosis may be different in humans and cats, and the anterior uveitis may represent a type of immune-mediated inflammation. A diagnosis is made by observing compatible clinical findings and obtaining supportive findings on serologic tests. Despite improved diagnostic techniques, including determination of IgM class antibodies and PCR testing, definitive diagnosis of ocular toxoplasmosis remains a challenge. Topical anti-inflammatory therapy should be used in cats with anterior uveitis, a positive serum titer, and no concurrent systemic signs. Systemic clindamycin should be given to cats with ocular and systemic signs and to cats with suggestive serology and idiopathic anterior uveitis that fails to respond to topical therapy alone.

Inflammatory diseases of the central nervous system in dogs.

Inflammatory diseases of the central nervous system (CNS) are important causes of seizures in dogs. Specific diseases include canine distemper, rabies, cryptococcosis, coccidioidomycosis, toxoplasmosis, neosporosis, Rocky Mountain spotted fever, ehrlichiosis, granulomatous meningoencephalomyelitis, and pug dog encephalitis. Inflammatory disorders should be considered when a dog with seizures has persistent neurological deficits, suffers an onset of seizures at less than 1 or greater than 5 years of age, or exhibits signs of systemic illness. A thorough history, examination, and analysis of cerebrospinal fluid are important in the diagnosis of inflammatory diseases. However, even with extensive diagnostic testing, a specific etiology is identified in less than two thirds of dogs with inflammatory diseases of the CNS.

Effect of interleukin-2 on experimental acute toxoplasmosis.

The traditional treatment of toxoplasmosis involves the use of pyrimethamine and sulphadiazine. This combination has a teratogenic effect and its use is limited especially in immunosuppressed cases. Spiramycin used safely during pregnancy is also not effective because it is toxoplasmistatic only. The potential efficiency of alternative immunotherapy was assessed. The present study was undertaken to evaluate the effect of exogenously supplied IL-2 on T. gondii infected mice. IL-2 was administered after infection (on days +2, +4, +6, +8), before and after infection (on days -3, -1, +2, +4, +6) and before infection (on days -8, -6, -4, -2). The date of infection was considered zero. Assessment of its effect was through: a) Parasitological study which included: parasite count, differentiation between living and dead tachyzoites and death rate of infection mice. b) Immunological study: detection of circulating antigen on the 3rd, 5th, 7th and 9th day p.i. The results showed that IL-2 was most effective when administered before and after infection in the form of significant reduction in parasitic count, least number of living tachyzoites, significant reduction in the death rate of infected mice and delayed appearance of circulating antigen with reduction in its level.

Parasitemia and parasitic loads in acute infection and after anti-gamma-interferon treatment in a toxoplasmic mouse model.

Toxoplasma gondii infection was induced in Swiss-Webster mice by intraperitoneal inoculation of avirulent Beverley strain cysts. We studied parasitemia and parasitic loads first in acute toxoplasmosis, then in the chronic stage of the disease. In the latter stage a group of mice received weekly administration of a rabbit antiserum directed against mouse gamma-interferon. Parasitemia, sequentially determined by amplification of the B1 gene using polymerase chain reaction, persisted for more than 1 month in acute toxoplasmosis. Brain and lung parasitic loads, assessed by a tissue-culture method, were significantly increased in mice treated with anti-interferon. Moreover, this increase was prevented by concomitant administration of pyrimethamine and sulfadiazine, suggesting that early prophylaxis would be suitable. Surprisingly, the anti-interferon treatment induced neither abnormal clinical signs nor a significant rise in the parasitemia level. Such a model seems to be particularly appropriate for the comparison of different strains of Toxoplasma gondii in a moderately immunodeficient state.

Production of nitric oxide (NO) is not essential for protection against acute Toxoplasma gondii infection in IRF-1-/- mice.

Production of nitric oxide (NO) by macrophages is important for the killing of intracellular pathogens. IFN-gamma and LPS stimulate NO production by transcriptional up-regulation of inducible nitric oxide synthetase (iNOS). In the present study we used mice with a targeted disruption of the IFN regulatory factor-1 gene (IRF-1-/-) to investigate the importance of NO in the host immune response against Toxoplasma gondii, a major cause of infection in newborns and those with AIDS. IRF-1-/- mice were more susceptible to acute Toxoplasma infection, and treatment with either exogenous IFN-gamma or in vivo neutralization of endogenous IFN-gamma had little effect on their susceptibility to infection. However, administration of exogenous IL-12 was able to prolong survival even when IFN-gamma was depleted. An in vivo depletion study suggested that the mechanism of this protective response is mediated in part by CD4+ T cells. The administration of IL-12 could not overcome the inhibition of lymphoproliferative response in T. gondii-infected mice and treatment with N-monomethyl-L-arginine (L-NMMA), a nitric oxide synthase (iNOS) antagonist in vitro was unable to reverse the immunosuppression. In response to Toxoplasma infection, splenocytes from IRF-1-/- mice exhibited increased production of IL-10 as well as a 30-fold increase in its message expression. These studies indicate that NO may not be essential for host immunity to the parasite, and moreover that IL-12 appears to induce an IFN-gamma-independent mechanism of protection against this opportunistic pathogen.

IL-1 beta is required for IL-12 to induce production of IFN-gamma by NK cells. A role for IL-1 beta in the T cell-independent mechanism of resistance against intracellular pathogens.

Mice with the severe combined immunodeficiency (SCID) possess an IFN-gamma-dependent mechanism of resistance to the intracellular pathogens Toxoplasma gondii and Listeria monocytogenes that is dependent on IL-12-induced production of IFN-gamma by NK cells. In this report we demonstrate that IL-1 beta is required for IL-12 to stimulate production of IFN-gamma by NK cells, and that IL-1 is important in IL-12-mediated resistance to T. gondii in vivo. Stimulation of SCID mouse splenocytes with tachyzoites of T. gondii resulted in production of IFN-gamma. Addition of neutralizing Ab specific for IL-1 beta to these cultures inhibited completely the production of IFN-gamma. Similar results were obtained when LPS or L. monocytogenes were used to stimulate production of IFN-gamma by SCID mouse splenocytes. Addition of a neutralizing Ab to IL-1 alpha did not affect production of IFN-gamma by SCID mouse splenocytes stimulated with T. gondii, L. monocytogenes, or LPS. Stimulation of SCID mouse splenocytes with IL-1 beta or IL-1 alpha did not result in production of IFN-gamma but enhanced remarkably the ability of T. gondii or IL-12 to stimulate production of IFN-gamma. Furthermore, production of IFN-gamma by SCID mouse splenocytes stimulated with IL-12 plus TNF-alpha was completely ablated by anti-IL-1 beta, but not by anti-IL-1 alpha. Analysis of the culture supernatants of spleen cells from SCID mice stimulated with T. gondii or IL-12 plus TNF-alpha detected low levels of IL-1 beta; addition of a neutralizing Ab to IFN-gamma resulted in a 5- to 10-fold increase in levels of IL-1 beta. Furthermore, stimulation of SCID mouse splenocytes with IL-12, in the presence of anti-IFN-gamma, resulted in an increase in detectable levels of IL-1 beta. To determine the in vivo relevance of our in vitro data, SCID mice were infected with T. gondii and treated with IL-12 alone or IL-12 in combination with an Ab specific for the type I IL-1 receptor. This Ab reduced production of IFN-gamma by SCID mouse splenocytes stimulated with either T. gondii, LPS, L. monocytogenes, or IL-12 plus IL-1 beta. In vivo administration of this Ab antagonized significantly the ability of exogenous IL-12 to delay the time to death of SCID mice infected with T. gondii.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of prolactin, rIFN-gamma or rTNF-alpha in murine toxoplasmosis.

Mice lethally infected with T. gondii and treated with prolactin (PRL), recombinant interferon gamma (rIFN-gamma) or recombinant tumour necrosis factor (rTNF-alpha) were protected against death, as compared to untreated controls. The protective effect of PRL (0.5-2 mg/kg/twice daily for 12 days) was dose dependent and statistically significant (P < 0.001). The survival was 50% or 40% in mice that received doses of 1 x 10(4) U of rIFN-gamma or 4 x 10(4) U of rTNF-alpha at -2, 0, +2 days before and after infection (P < 0.0001). An increase of time to death, up to 60 days after challenge, and of survival rate (50% up to 70%) were observed in animals treated with PRL in combination with either rTNF-alpha or rIFN-gamma, compared to those that received treatments with the same therapeutic agents alone; however the differences were not statistically significant. In addition, a slight synergistic effect on brain cyst formation, with lower number of Toxoplasma cysts, was observed in mice treated with PRL plus TNF-alpha (P < 0.01), compared with animals that received rTNF-alpha alone (P < 0.05). These data suggest that PRL can regulate in vivo endogenous TNF-alpha production in the cytokine cascade. We conclude that prolactin may play an important role in modulating the host's immune defence against T. gondii opportunistic infection.

Transforming growth factor-beta inhibits interleukin-12-induced production of interferon-gamma by natural killer cells: a role for transforming growth factor-beta in the regulation of T cell-independent resistance to Toxoplasma gondii.

Severe-combined immune deficient (SCID) mice have been found to resist infection with the intracellular protozoan parasite Toxoplasma gondii via interleukin (IL)-12 stimulation of interferon (IFN)-gamma production by natural killer (NK) cells. Previously, we demonstrated the presence of increased levels of transcripts for transforming growth factor-beta (TGF-beta) in the brains and lungs of SCID mice infected with T. gondii, leading us to investigate the role of TGF-beta in the mechanism of resistance to T. gondii in these mice. Stimulation of splenocytes from SCID mice with heat-killed T. gondii resulted in production of low levels of IFN-gamma and a two to threefold increase in levels of TGF-beta in the culture supernatants. Production of IFN-gamma in these cultures was increased three to fourfold by addition of anti-TGF-beta antibody. Stimulation of splenocytes from SCID mice with IL-12 in combination with either TNF-alpha or IL-1 beta resulted in production of high levels of IFN-gamma. Addition of TGF-beta to these cultures inhibited production of IFN-gamma in a dose-dependent manner. Immunohistochemical studies revealed increased levels of TGF-beta protein in the spleens of SCID mice 5 days after oral infection with the ME49 strain of T gondii, and brains of SCID mice at 18 days post-infection. However, no difference was detected in the levels of TGF-beta transcripts in the spleens of uninfected mice or mice infected for 5 days. To test whether TGF-beta could antagonize IL-12 mediated resistance to T. gondii in vivo, we administered TGF-beta to SCID mice infected with T. gondii. This treatment resulted in earlier mortality of infected mice and significantly reduced the ability of exogenous IL-12 to delay time-to-death. Administration of anti-TGF-beta to SCID mice, beginning 24 h prior to infection and every 2 days thereafter, delayed significantly time-to-death. Together, our data demonstrate that TGF-beta antagonizes the ability of IL-12 to stimulate production of IFN-gamma by splenocytes from SCID mice, and suggest a role for TGF-beta in regulation of T cell-independent resistance to T. gondii.

Studies on the role of interleukin-12 in acute murine toxoplasmosis.

Interleukin-12 (IL-12) is important in the regulation of resistance to Toxoplasma gondii in mice with severe combined immunodeficiency (SCID). The protective ability of IL-12 in SCID mice appears to be through its activity on natural killer (NK) cells to induce production of interferon-gamma (IFN-gamma). In this study we assessed the role of IL-12 in the acute stage of toxoplasmosis in immunocompetent mice. Administration of IL-12 to BALB/c mice infected with the virulent C56 strain of T. gondii remarkably delayed time to death. The protective activity of IL-12 was abrogated by administration of monoclonal antibodies to IFN-gamma or tumour necrosis factor-alpha (TNF-alpha), and by depletion of NK cells using an antisera against asialoGM1. Whereas BALB/c mice infected with the ME49 strain of T. gondii survived infection, administration of anti-IL-12 to infected mice resulted in 100% mortality accompanied by decreased serum levels of IFN-gamma. Furthermore, this treatment significantly reversed the suppression of spleen cell proliferation to concanavalin A (Con A), which is associated with the acute stage of infection, and resulted in decreased ex vivo production of IFN-gamma, IL-2, IL-4 and IL-10 in response to Con A. Our results indicate an important role for IL-12 in mediating resistance to T. gondii during acute infection in immunocompetent mice, that NK cells are required for this protective activity, and that IL-12 is involved in the immunosuppression which accompanies this infection.

Antibody against interleukin-6 reduces inflammation and numbers of cysts in brains of mice with toxoplasmic encephalitis.

Treatment of toxoplasmic encephalitis in C57BL/6 mice with monoclonal antibody (MAb) against interleukin-6 (IL-6) resulted in a remarkable decrease in the number of foci of acute inflammation in their brains caused by proliferation of tachyzoites. In brains of mice treated with isotype control MAb and those treated with anti-IL-6 MAb, tachyzoites were observed only in foci of acute inflammation. Immunoperoxidase staining revealed a greatly diminished frequency of tachyzoites in brains of mice treated with anti-IL-6 MAb. Of interest, treatment with MAb against IL-6 was also associated with reduced numbers of Toxoplasma gondii cysts in the brains and with higher serum levels of gamma interferon than in control mice. Paradoxically, the mice treated with anti-IL-6 MAb had higher serum levels of IL-6 as measured by an enzyme-linked immunosorbent assay than controls. These results revealed the importance of IL-6 in the immunopathogenesis of murine toxoplasmic encephalitis.

Interleukin-12.

Interleukin-12 (IL-12) is a newly characterized cytokine that has a unique heterodimeric structure. It was initially cloned from B lymphoblastoid cell lines, but the majority of IL-12 is produced by macrophages/monocytes following appropriate stimulation. IL-12 can (1) enhance the cytolytic activity of a number of effector cells including T cells, natural killer (NK) cells, lymphokine activated killer (LAK) cells, and macrophages, (2) increase proliferation of activated NK and T cells, (3) induce production of cytokines, such as interferon gamma, (4) stimulate the induction of TH1 cells, (5) upregulate a number of cell surface molecules, (6) inhibit IgE secretion, and (7) act as a synergistic factor for hematopoietic stem cells. Based on these potent immunomodulatory activities, IL-12 has been evaluated in several disease models for parasitic infections and malignancies. Marked activity of IL-12 against both Leishmania and Toxoplasma has been reported. Likewise, antimetastatic and antitumor activity, including tumor regression, has been observed against a number of murine malignancies treated with IL-12 using doses that result in little toxicity. The results suggest that IL-12 may be a useful cytokine for the treatment of a number of diseases.