Antimicrobial properties of Kupffer cells.

To characterize the antimicrobial activities of Kupffer cells, I harvested macrophages from livers with a technique involving perfusion with collagenase and DNase. Ninety-nine percent of glass-adherent cells had typical macrophage morphology, 99% were esterase positive, and 60% phagocytosed opsonized zymosan when challenged with four particles per macrophage. Toxoplasma gondii multiplied within Kupffer cells from unmanipulated mice, but multiplication was intermediate between that observed in highly permissive peritoneal macrophages and highly activated macrophages. Intravenous injection of heat-killed Propionibacterium acnes, a stimulus known to activate macrophages in other compartments, resulted in a uniform, highly activated population of liver macrophages. Kupffer cells from P. acnes-injected mice were capable of generating reactive oxygen intermediates as shown by reduction of Nitro Blue Tetrazolium during phagocytosis of T. gondii or opsonized zymosan. In contrast, intravenous P. acnes injection did not activate spleen macrophages. Intravenous injection of P. acnes into athymic mice activated Kupffer cells, which suggested that T cells were not essential for this response. Kupffer cells were not activated in mice with latent Toxoplasma infection or during acute Giardia muris infection. Ordinarily, Kupffer cells became highly permissive for T. gondii during 48 h in culture, but inclusion of recombinant murine gamma interferon maintained their moderate inhibitory activity.     

Vaccination against murine toxoplasmosis using recombinant Toxoplasma gondii SAG3 antigen alone or in combination with Quil A

PURPOSE: Surface antigen 3 (SAG3) of Toxoplasma gondii is very similar in structure to the major surface antigen 1 (SAG1). Although numerous studies have supported the importance of SAG1 in protection against T. gondii infection, few reports exist on SAG3. MATERIALS AND METHODS: Glutathione-S-transferase (GST)-fused SAG3 of T. gondii (rSAG3) were immunized into BALB/c mice alone or in combination with Quil A (rSAG3/Quil A), and then evaluated the protective immunity in vivo and in vitro against murine toxoplasmosis. RESULTS: Immunization with rSAG3 or rSAG3/Quil A resulted in significantly more survival days and fewer brain cysts after challenge with T. gondii compared to an infected control group. Mice immunized with rSAG3 alone or in combination with Quil A produced significantly more specific IgG2a antibody, whereas specific IgG1 antibody titers did not increase. The percentage of CD8+ T cells, IFN-gamma mRNA expression, and nitric oxide production significantly increased in rSAG3- and rSAG3/Quil A-immunized mice. CONCLUSION: These results indicate that vaccination with Toxoplasma rSAG3 results in partial protective immunity against T. gondii infection through induction of a Th1-type immune response, and that protective immunity is accelerated by the modulating effects of Quil A.     

Microbicidal activities of Salmonella typhimurium- and interferon-gamma-activated mouse peritoneal macrophages

Activation of mouse peritoneal macrophages during infection of mice by various facultative intracellular bacteria and after intravenous injection of recombinant interferon-gamma (rIFN-gamma) was studied. Macrophage activation was demonstrated on the basis of three different criteria, i.e. inhibition of Toxoplasma gondii proliferation, enhanced release of H2O2 and increased expression of Ia antigen. Macrophages activated during an infection with Salmonella typhimurium showed no enhanced salmonellacidal or listericidal activity relative to control macrophages, whereas Listeria-activated macrophages killed Listeria but not Salmonella faster than control macrophages. The rate of proliferation of Salmonella in spleen and liver of activated mice was comparable to the proliferation in the organs of control mice. rIFN-gamma-activated macrophages displayed neither an enhanced salmonellacidal nor an enhanced listericidal activity. When high numbers of Listeria were injected intravenously the proliferation in spleen and liver of rIFN-gamma-treated and control mice was similar. The proliferation of Listeria in the liver of rIFN-gamma-treated mice was less than in control mice when 1 LD50 or lower numbers of bacteria were injected. It is concluded that peritoneal macrophages become activated during infections of mice with various intracellular pathogens. However, these activated macrophages do not show enhanced bactericidal activity against all bacteria. Furthermore, rIFN-gamma is not sufficient to enhance the listericidal activity of macrophages.     

Effects of Corynebacterium parvum treatment and Toxoplasma gondii infection on macrophage-mediated cytostasis of tumour target cells.

Injection of mice with Corynebacterium parvum or living or killed Toxoplasma gondii was studied to determine the efficacy of these treatments in activating peritoneal macrophages to inhibit the uptake of [3H]TdR (cytostasis) by tumour target cells in vitro. In the presence of activated macrophages from mice treated i.p. with a wide dose range of either C. parvum or living Toxoplasma, cytostasis was usually greater than 99%. This population of activated macrophages was transient in C. parvum-treated mice, but persists, probably for life, in Toxoplasma-infected mice. Whereas the i.p. route of administration of C. parvum was more efficient in activating macrophages than the i.v. route, the s.c. route appeared to be relatively ineffective. Treatment with killed Toxoplasma by any route was also relatively ineffective in activating macrophages. In contrast Toxoplasma infection resulted in highly activated peritoneal macrophages, regardless of the route of administration. Depending upon the route of initial treatment, the route of readministration of C. parvum had either no appreciable effect or resulted in a marked alteration in the cytostatic capacity of peritoneal macrophages.     

gamma delta T cells play a crucial role in the expression of 65,000 MW heat-shock protein in mice immunized with Toxoplasma antigen.

Toxoplasma gondii is an obligate intracellular protozoan parasite and cellular immunity plays a crucial role in protection against infection with this pathogen. When mice are immunized with Toxoplasma homogenate, they readily acquire resistance against infection with a lethal dose of a low virulence Beverley strain of T. gondii. We have reported previously that expression of 65,000 MW heat-shock protein (hsp 65) in host macrophages closely correlates with protective potentials of hosts, while this protein is not expressed in Toxoplasma themselves. In this study, we examined the mechanism of expression of hsp 65 in mice immunized with Toxoplasma homogenate. Heat-shock protein was detected in peritoneal macrophages of BALB/c mice immunized 7 days previously by electroblot assay with a specific monoclonal antibody (mAb) for microbial hsp 65. Furthermore, an immunogold ultracytochemistry assay demonstrated that this protein was expressed on the cell surface of peritoneal macrophages in immune mice. This expression was not induced in those of immune athymic nude mice and SCID mice. Treatment of BALB/c mice with anti-Thy-1.2 mAb 1 day before immunization led to an almost complete loss of the expression of hsp 65. To determine the subsets of T cells responsible for induction of this protein, mice were depleted of gamma delta T cells, alpha beta T cells, CD4+ T cells or CD8+ T cells by treating with corresponding antibodies before immunization. From these experiments, gamma delta T cells were shown to be essential for the expression of hsp 65, although CD4+ alpha beta T cells also contributed to some extent. Thus, gamma delta T cells appear to play an important role in protective immunity against infection with T. gondii through mediating the expression of hsp 65 in host macrophages.     

Coumarin or warfarin treatment of mice does not increase the microbicidal or tumoricidal capacities of macrophages.

Benzopyrones have been shown to affect several functions of macrophages. We examined the effects of two benzopyrones, coumarin and warfarin, on the capacity of mouse macrophages to inhibit microorganisms and tumour target cells. Mice were treated with daily i.v. doses of either drug. Then the mice were challenged with lethal doses of Toxoplasma gondii or peritoneal macrophages from these mice were challenged in vitro with T. gondii or tumour target cells Survival of coumarin or warfarin-treated mice challenged with T. gondii was similar to that of control mice. Multiplication of T gondii and growth of tumour target cells were similar in preparations of macrophages from coumarin-treated, warfarin-treated, or control mice and were inhibited in preparations of activated macrophages from Corynebacterium parvum-treated mice that served as positive controls. Under our experimental conditions, benzopyrones did not activate mouse macrophages.     

Role for Activated Macrophages in Resistance Against Trichinella spiralis

To determine whether activated macrophages are important in resistance against the intestinal phase of nematode parasites, we studied Trichinella spiralis infections in mice with normal macrophages and in mice with macrophages activated by either chronic Toxoplasma gondii or acute Listeria monocytogenes infections. The peak T. spiralis adult worm burden in the intestines of normal C57BL/6 or Swiss Webster mice occurred from 6 to 14 days after infection. Subsequent expulsion of worms from the intestines occurred from 8 to 20 days after infection. C57BL/6 mice chronically infected with T. gondii and then challenged with T. spiralis larvae had significantly lower peak intestinal worm burdens (P < 0.05) than normal C57BL/6 mice similarly challenged. Swiss Webster mice infected 7 or 13 days earlier with L. monocytogenes and then challenged with T. spiralis larvae had significantly lower peak worm burdens (P < 0.01) than uninfected mice. The time of expulsion of adult worms was not affected by either infection. Swiss Webster mice infected 42 days earlier with L. monocytogenes (i.e., possessing lymphocytes sensitized to L. monocytogenes but not possessing activated macrophages) did not have a lower worm burden than uninfected mice. Serum factors (e.g., antibody) did not appear to play a role because normal mice injected with serum from L. monocytogenes-infected mice had worm burdens similar to those of mice injected with normal serum. The histopathology of intestines of mice infected with T. gondii or L. monocytogenes was the same as that of normal mice. When T. spiralis larvae were incubated with normal macrophages or macrophages from T. spiralis-infected mice in vitro for 24 h, the number of larvae with adherent T. spiralis macrophages was significantly (P < 0.005) greater than the number of larvae with adherent normal macrophages. These studies suggest a role for activated macrophages in resistance to T. spiralis.     

Infection with Toxoplasma gondii reduces established and developing Th2 responses induced by Nippostrongylus brasiliensis infection

Oral infection of C57BL/6 mice with 100 cysts of the protozoan parasite Toxoplasma gondii results in the development of small intestinal Th1-type immunopathology. In contrast, infection with intestinal helminths results in the development of protective Th2-type responses. We investigated whether infection with the helminth Nippostrongylus brasiliensis influences the development of T. gondii-induced Th1 responses and immunopathology in C57BL/6 mice infected with T. gondii. Prior as well as simultaneous infection of mice with N. brasiliensis did not alter the course of infection with 100 cysts of T. gondii. Coinfected mice produced high levels of interleukin-12 (IL-12) and gamma interferon (IFN-gamma), developed small intestinal immunopathology, and died at the same time as mice infected with T. gondii. Interestingly, local and systemic N. brasiliensis-induced Th2 responses, including IL-4 and IL-5 production by mesenteric lymph node and spleen cells and numbers of intestinal goblet cells and blood eosinophils, were markedly lower in coinfected than in N. brasiliensis-infected mice. Similar effects were seen when infection with 10 T. gondii cysts was administered following infection with N. brasiliensis. Infection of C57BL/6 mice with 10 T. gondii cysts prior to coinfection with N. brasiliensis inhibited the development of helminth-induced Th2 responses and was associated with higher and prolonged N. brasiliensis egg production. In contrast, oral administration of Toxoplasma lysate prior to N. brasiliensis infection had only a minor and short-lived effect on Th2 responses. Thus, N. brasiliensis-induced Th2 responses fail to alter T. gondii-induced Th1 responses and immunopathology, most likely because Th1 responses develop unchanged in C57BL/6 mice with a prior or simultaneous infection with N. brasiliensis. Our findings contribute to the understanding of immune regulation in coinfected animals and may assist in the design of immunotherapies for human Th1 and Th2 disorders.     

Humoral responses and immune protection in mice immunized with irradiated T. gondii tachyzoites and challenged with three genetically distinct strains of T. gondii

Toxoplasma gondii is an obligate intracellular parasite that infects a variety of mammals and birds. T. gondii also causes human toxoplasmosis; although toxoplasmosis is generally a benign disease, ocular, congenital or reactivated disease is associated with high numbers of disabled people. Infection occurs orally through the ingestion of meat containing cysts or by the intake of food or water contaminated with oocysts. Although the immune system responds to acute infection and mediates the clearance of tachyzoites, parasite cysts persist for the lifetime of the host in tissues such as the eye, muscle, and CNS. However, T. gondii RH strain tachyzoites irradiated with 255Gy do not cause residual infection and induce the same immunity as a natural infection. To assess the humoral response in BALB/c and C57BL/6J mice immunized with irradiated tachyzoites either by oral gavage (p.o.) or intraperitoneal (i.p.) injection, we analyzed total and high-affinity IgG and IgA antibodies in the serum. High levels of antigen-specific IgG were detected in the serum of parenterally immunized mice, with lower levels in mice immunized via the oral route. However, most serum antibodies exhibited low affinity for antigen in both mice strain. We also found antigen specific IgA antibodies in the stools of the mice, especially in orally immunized BALB/c mice. Examination of bone marrow and spleen cells demonstrated that both groups of immunized mice clearly produced specific IgG, at levels comparable to chronic infection, suggesting the generation of IgG specific memory. Next, we challenged i.p. or p.o. immunized mice with cysts from ME49, VEG or P strains of T. gondii. Oral immunization resulted in partial protection as compared to challenged naive mice; these findings were more evident in highly pathogenic ME49 strain challenge. Additionally, we found that while mucosal IgA was important for protection against infection, antigen-specific IgG antibodies were involved with protection against disease and disease pathogenesis. Most antigen responsive cells in culture produced specific high-affinity IgG after immunization, diverse of the findings in serum IgG or from cells after infection, which produced low proportion of high-avidity IgG.     

Effect of alveolar macrophages on Toxoplasma gondii.

As pulmonary involvement can occur in disseminated toxoplasmosis in immunosuppressed patients, studies were initiated to define local mechanisms of resistance of the lung to Toxoplasma gondii. Alveolar macrophages were obtained from normal mice and mice chronically infected with T. gondii by bronchopulmonary lavage and cultured in vitro. Although normal alveolar macrophages were difficult to infect with Toxoplasma, they supported intracellular multiplication of this organism. When exposed to Toxoplasma that had been pretreated with heat-inactivated serum containing specific antibody, the number of intracellular organisms increased remarkably, and the macrophages destroyed the coated parasites. After development of chronic infections with Toxoplasma, there was a transient period during which a striking increase in numbers of alveolar macrophages was observed in lavage specimens. These macrophages differed from those of normal alveolar macrophages. There was a greater percentage of large cells, a greater tendency to spread on glass, and an increased number of intracellular Toxoplasma, and the cells were activated to kill or inhibit multiplication of the parasite. During the period when activated macrophages were demonstrable in bronchopulmonary washings, histological changes in the lungs revealed a marked mononuclear cell infiltrate. These studies support a role for the activated alveolar macrophage as an effector in resistance of the lung to infection with Toxoplasma.     

Immune responses and resistance to Toxoplasma gondii in mice immunized with antigens of the parasite incorporated into immunostimulating complexes.

Immunostimulating complexes were prepared with antigens extracted from tachyzoites of Toxoplasma gondii and were used to immunize mice. The major antigens incorporated into the immunostimulating complexes were the P30 and P22 antigens and an antigen with an approximate molecular weight of 6,000. Other antigens of molecular weights above 30,000 were also present. High antibody titers to T. gondii antigens and a delayed-type hypersensitivity reaction were noted for the immunized mice. Challenge of these mice with tachyzoites injected interperitoneally or with oocysts administered orally resulted in a statistically significant (P < 0.001) conditional probability of survival compared with that of controls. In contrast, the differences between immunized mice and controls challenged with tissue cysts did not attain statistical significance.     

TLR2 as an essential molecule for protective immunity against Toxoplasma gondii infection

To investigate the role of the Toll-like receptor (TLR) family in host defense against Toxoplasma gondii, we infected TLR2-, TLR4- and MyD88-deficient mice with the avirulent cyst-forming Fukaya strain of T. gondii. All TLR2- and MyD88-deficient mice died within 8 days, whereas all TLR4-deficient and wild-type mice survived after i.p. infection with a high dose of T. gondii. Peritoneal macrophages from T. gondii-infected TLR2- and MyD88-deficient mice did not produce any detectable levels of NO. T. gondii loads in the brain tissues of TLR2- and MyD88-deficient mice were higher than in those of TLR4-deficient and wild-type mice. Furthermore, high levels of IFN-gamma and IL-12 were produced in peritoneal exudate cells (PEC) of TLR4-deficient and wild-type mice after infection, but low levels of cytokines were produced in PEC of TLR2- and MyD88-deficient mice. On the other hand, high levels of IL-4 and IL-10 were produced in PEC of TLR2- and MyD88-deficient mice after infection, but low levels of cytokines were produced in PEC of TLR4-deficient and wild-type mice. The most remarkable histological changes with infiltration of inflammatory cells were observed in lungs of TLR2-deficient mice infected with T. gondii, where severe interstitial pneumonia occurred and abundant T. gondii were found.     

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.     

The MIC3 gene of Toxoplasma gondii is a novel potent vaccine candidate against toxoplasmosis

Infection with the intracellular protozoan parasite Toxoplasma gondii causes serious public health problems and is of great economic importance worldwide. The micronemal protein MIC3, which is a potent adhesin of T. gondii, could be a significant candidate vaccine against toxoplasmosis. In this study, all CBA/J mice intramuscularly vaccinated with a plasmid encoding the immature form of the MIC3 protein (pMIC3i) produced specific anti-MIC3 immunoglobulin G (IgG) antibodies, and their sera displayed high antibody titers. This response was increased by the coadministration of a plasmid encoding the granulocyte-macrophage colony-stimulating factor (pGM-CSF). Similarly, a specific and significant cellular immune response was obtained in mice immunized with pMIC3i, and this response was markedly enhanced by pGM-CSF coadministration. The cellular immune response was associated with the production of gamma interferon IFN-gamma and interleukin-2 (IL-2), indicating that this was a Th1-type response. This was confirmed by the production of large amounts of IgG2a. Mice immunized with pMIC3i displayed significant protection against an oral challenge with T. gondii 76K cysts, exhibiting fewer brain cysts than did the control mice. Coadministration of pGM-CSF enhanced this protection. In conclusion, this study describes the design of a potent DNA vaccine encoding the novel T. gondii target antigen, MIC3 protein, that elicits a strong specific immune response as well as providing effective protection against T. gondii infection. In the attempt to achieve complete protection against toxoplasmosis, MIC3 is a good candidate vaccine which could be combined with other relevant and previously described candidates, such as SAG1 and GRA4.     

Effects of muramyl dipeptide and trehalose dimycolate on resistance of mice to Toxoplasma gondii and Acanthamoeba culbertsoni infections

The effects of synthetic muramyl dipeptide (MDP) and natural trehalose dimycolate (TDM) against parasitic infections by intracellular Toxoplasma gondii and free-living Acanthamoeba culbertsoni were studied. Significant resistance against oral T. gondii infection was induced by intraperitoneal pretreatment with TDM but not with MDP. The protective effect of TDM against T. gondii was corroborated by a significant reduction in the number of cysts in brains of pretreated animals and elevated serum antibody levels. Partial protection against lethal intranasal A. culbertsoni infection was conferred by specific immunization with viable trophozoites of nonpathogenic Acanthamoeba lugdunensis. The nonspecific resistance induced by intravenous pretreatment with MDP was similar to, whereas that stimulated by TDM was lesser than the protection conferred by A. lugdunensis. The Fc receptor-mediated phagocytosis of 51Cr-labeled sheep red blood cells by alveolar macrophages was enhanced by MDP. The phagocytic activity of peritoneal macrophages was increased by lower doses of TDM.     

Studies of macrophage function during Trichinella spiralis infection in mice.

Studies were made to investigate the quantitative and functional changes which occur in peritoneal macrophage populations obtained from mice infected orally with Trichinella spiralis larvae. C57BL/6 mice infected with T. spiralis larvae became parasitized with adult worms which were rejected from the intestine from 14 to 20 days after infection. Infected mice developed a striking increase in peritoneal exudate cells, composed largely of macrophages, which was maximal at from 16 to 18 days after infection. T. spiralis larvae and eosinophils were not seen in the peritoneal exudates. Macrophages from mice infected more than 11 days earlier inhibited DNA synthesis of syngeneic and allogeneic tumour cells, a property atributed to activated macrophages. In addition, macrophages from T. spiralis-infected mice had the functional ability to kill EL-4 tumour cells as measured by 51Cr release. Unlike activated macrophages, however, macrophages from infected mice did not develop the ability to inhibit multiplication of the intracellular pathogen Toxoplasma gondii. These studies demonstrate that T. spiralis infection in mice induces changes in macrophage function that differ from changes associated with infections by intracellular pathogens.     

Dissociative Effects of a Novel Immunomodulating Agent (CP-20,961) on Host Defenses of Mice

Abstract

The antimicrobial and antitumor effects of CP-20, 961, a synthetic lipoid amine with immunomodulating properties, were investigated. Mice given CP-20,961 ip seven or three days before challenge with ip Listeria monocytogenes had a lower mortality than control mice. By contrast, CP-20,961 did not protect against lethal challenges of either Salmonella typhimurium or Toxoplasma gondii. In parallel with the in vivo studies, peritoneal macrophages from CP-20, 961-injected mice inhibited multiplication of L. monocytogenes but not T. gondii. Further studies demonstrated that CP-20,961 protected mice against an ip challenge of P815 tumor cells as measured by survival time. This correlated with the ability of simulated peritoneal macrophages to inhibit (³H-TdR uptake inhibition) and kill (Cr⁵¹ release) P815 cells in vitro. These data indicate that CP-20,961 affords protection against an ascitic mastocytoma tumor line and at least one, but not all. intracellular pathogens. The dissociation of the immunomodulating effect, which was reflected in peritoneal macrophage function, may be characteristic of this new class of immunomodulators.     

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.     

Effect of recombinant tumour necrosis factor on acute infection in mice with Toxoplasma gondii or Trypanosoma cruzi.

Recombinant tumor necrosis factor (rTNF) has been shown to protect mice against lethal bacterial infections. We previously reported that in in vitro experiments with mouse peritoneal macrophages, rTNF inhibited intracellular multiplication of Trypanosoma cruzi but not of Toxoplasma gondii. These disparate results led us to study the effect of rTNF on the in vivo infection with these parasites. Daily administration of 0.5 and 5.0 micrograms rTNF resulted in a dose-dependent, significantly decreased time to death (p less than 0.05) in mice infected with lethal doses of T. cruzi. The same effect was found in mice infected with T. gondii and given a daily dose of 5.0 micrograms rTNF. Lower doses of rTNF did not significantly affect time to death of mice infected with either parasite.     

Specific antibody-dependent killing of Toxoplasma gondii by normal macrophages.

The requirement for specificity of antibody-dependent inhibition or killing of intracellular Toxoplasma gondii trophozoites by normal mouse peritoneal macrophages was evaluated in vitro using light microscopy and autoradiography. Anti-toxoplasma antibody in the presence of 'accessory factor' rendered extracellular T. gondii trophozoites non-viable and non-infectious for cells, whereas exposure of extracellular trophozoites to heat-inactivated immune serum did not appear to damage the parasites. Although pretreatment of extracellular trophozoites with heat-inactivated immune serum neither diminished nor prevented infection of normal mouse peritoneal macrophages, it did confer upon macrophages the ability to inhibit or kill the organisms once they were intracellular. In contrast, pretreatment of trophozoites with either heat-inactivated normal or Besnoitia jellisoni immune serum did not enable normal macrophages to inhibit or kill T. gondii; rather, such organisms multiplied intracellularly in normal macrophages. Thus, pretreatment with specific antibody alone prepared T. gondii trophozoites for intracellular destruction by normal mouse peritoneal macrophages. These results suggest that spesific antibody acting in concert with normal macrophages may play a role in controlling infection with T. gondii.