Nitric Oxide Mediates the Toxoplasmastatic Activity of Murine Microglial Cells in vitro

Toxoplasma gondii (T. gondii), an opportunistic protozoan, is an important cause of central nervous system (CNS) infections in immunosuppressed patients. The present study focused on the interaction between T. gondii and microglial cells from the brain of neonatal Balb/c mice.

Preincubation of the murine microglial cells with recombinant interferon-gamma (rIFN-gM) and lipopolysaccharide (LPS) induced significant inhibition of T. gondii replication in a dose dependent manner. This antiparasitic effect in microglial cells was correlated with the induction of the L-arginine-dependent generation of reactive nitrogen intermediates (RNIs). Tumor necrosis factor-alpha (TNF-aL) was also involved in the toxoplasmastatic activity. Microglial cells incubated with recombinant TNF-aL in combination with a non-activating concentration of rIFN-gM released substantial amount of RNIs. Neutralizing antibodies against mouse TNF-aL inhibited the release of RNI by rIFN-gM activated macrophages.

In summary, the present results show that activation of microglial cells by rIFN-gM and LPS induce the production of nitric oxide (NO) by these cells via an L-arginine dependent pathway. NO appears to be the effector molecule mediating the toxoplasmastatic effects in these cells.     

Rat intestinal epithelial cell line IEC-6 is activated by recombinant inferferon-γ to inhibit replication of the coccidian Toxoplasma gondii

Toxoplasma gondii tachyzoites invaded and replicated in cultured rat small intestine cells of the line IEC-6. Treatment of rat small intestine cells with murine recombinant interferon-y resulted in a dose-dependent inhibition of intracellular T. gondii replication. This could be of relevance as a first line defense against Toxoplasma infection.     

Toxoplasma gondii prevents neuron degeneration by interferon-gamma-activated microglia in a mechanism involving inhibition of inducible nitric oxide synthase and transforming growth factor-beta1 production by infected microglia

Interferon (IFN)-gamma, the main cytokine responsible for immunological defense against Toxoplasma gondii, is essential in all infected tissues, including the central nervous system. However, IFN-gamma-activated microglia may cause tissue injury through production of toxic metabolites such as nitric oxide (NO), a potent inducer of central nervous system pathologies related to inflammatory neuronal disturbances. Despite potential NO toxicity, neurodegeneration is not commonly found during chronic T. gondii infection. In this study, we describe decreased NO production by IFN-gamma-activated microglial cells infected by T. gondii. This effect involved strong inhibition of iNOS expression in IFN-gamma-activated, infected microglia but not in uninfected neighboring cells. The inhibition of NO production and iNOS expression were parallel with recovery of neurite outgrowth when neurons were co-cultured with T. gondii-infected, IFN-gamma-activated microglia. In the presence of transforming growth factor (TGF)-beta1-neutralizing antibodies, the beneficial effect of the parasite on neurons was abrogated, and NO production reverted to levels similar to IFN-gamma-activated uninfected co-cultures. In addition, we observed Smad-2 nuclear translocation, a hallmark of TGF-beta1 downstream signaling, in infected microglial cultures, emphasizing an autocrine effect restricted to infected cells. Together, these data may explain a neuropreservation pattern observed during immunocompetent host infection that is dependent on T. gondii-triggered TGF-beta1 secretion by infected microglia.     

Endogenous tumor necrosis factor alpha is required for enhanced antimicrobial activity against Toxoplasma gondii and Listeria monocytogenes in recombinant gamma interferon-treated mice.

In vitro studies have shown that macrophages stimulated with recombinant gamma interferon (rIFN-gamma) produce tumor necrosis factor alpha (TNF-alpha), which in an autocrine fashion activates these cells. The aim of the present study was to determine whether endogenously formed TNF-alpha also is required for rIFN-gamma-induced macrophage activation and enhanced antimicrobial activity in vivo. After an intraperitoneal injection of rIFN-gamma into CBA/J mice, their peritoneal macrophages released enhanced amounts of NO2- and inhibited the intracellular proliferation of Toxoplasma gondii. Injection of neutralizing antibodies against TNF-alpha simultaneously with the rIFN-gamma completely inhibited both the release of NO2- by macrophages and their toxoplasmastatic activity. Similar results were observed after intraperitoneal injection of a competitive inhibitor of L-arginine, NG-monomethyl-L-arginine, together with rIFN-gamma, demonstrating that in vivo L-arginine-derived reactive nitrogen intermediates are essential for the induction of toxoplasmastatic activity. Intravenous injection of rIFN-gamma inhibited the growth of Listeria monocytogenes in the livers and spleens of mice; this effect was abrogated by antibodies against TNF-alpha. Intravenous injection of a large dose of rTNF-alpha resulted in a decrease in the number of bacteria in the liver and spleen, but an injection of rIFN-gamma and rTNF-alpha did not result in enhanced inhibition of the proliferation of L. monocytogenes. Together, the results of the present study are the first to demonstrate that endogenous TNF-alpha is required in vivo for the expression of macrophage activation with respect to the release of reactive nitrogen intermediates and toxoplasmastatic activity and for enhanced listericidal activity in the livers and spleens of mice stimulated with rIFN-gamma.     

Nitric oxide is not involved in the killing of Trypanosoma cruzi by chicken macrophages

It is known that chicken macrophages derived in vitro from blood monocytes have the capacity to destroy Trypanosoma cruzi, but Toxoplasma gondii can survive within these cells. This study was performed to determine the involvement of nitric oxide (NO) in the killing of T. cruzi by chicken macrophages. Activated (by interferon-γ and lipopolysaccharide) mouse peritoneal macrophages were used as controls. Macrophages were infected with T. cruzi and T. gondii; after 2, 24, and 48 h, NO was assayed using the Griess reagent. Respiratory-burst involvement, revealed by the reduction of nitroblue tetrazolium (NBT), was determined in chicken macrophages. Chicken macrophages did not produce NO; mouse macrophages were capable of producing NO with no multiplication of parasites. Reduction of NBT could be detected in chicken macrophages that interacted with T. cruzi but was absent in those that interacted with T. gondii. These results demonstrate that chicken macrophages do not use NO as a microbicidal agent when infected with T. cruzi or T. gondii. Received: 1 June 1999 / Accepted: 18 August 1999     

Autophagy activated by Toxoplasma gondii infection in turn facilitates Toxoplasma gondii proliferation

Autophagy was found to play an antimicrobial or antiparasitic role in the activation of host cells to defend against intracellular pathogens, at the same time, pathogens could compete with host cell and take advantage of autophagy to provide access for its proliferation, but there are few articles for studying the outcome of this competition between host cell and pathogens. Therefore, the aim of our study was to investigate the relationship between autophagy activated by Toxoplasma gondii (T. gondii) and proliferation of T. gondii affected by autophagy in vitro. Firstly, human embryonic fibroblasts (HEF) cells were infected with T. gondii for different times. The monodansylcadaverine (MDC) staining, acridine orange (AO) staining, punctuate GFP-LC3 distribution, and transmission electron microscopy (TEM) assays were conducted, and the results were consistent in showing that gondii infection could induce autophagy. Secondly, HEF cells were infected with T. gondii and treated with autophagy inhibitor bafilomycin A1 or inducer lithium chloride for different times. Giemsa staining was conducted, and the results exhibited that T. gondii infection-induced autophagy could in turn promote T. gondii proliferation. Simultaneously, the results of Giemsa staining also revealed that autophagy inhibitor could reduce the number of each cell infected with T. gondii and inhibit T. gondii proliferation. In contrast, autophagy inducer could increase the number of each cell infected with T. gondii and encourage T. gondii proliferation. Therefore, our study suggests that T. gondii infection could activate autophagy, and this autophagy could in turn facilitate T. gondii proliferation in HEF cells for limiting nutrients.     

Involvement of tumor necrosis factor-α during infection of human monocytic cells by Toxoplasma gondii

Although the involvement of tumor necrosis factor-α (TNF-α) during Toxoplasma gondii infection has largely been described in mouse models, only a few studies in human models have been reported. We demonstrated the role of TNF-α during the process of invasion by T. gondii in human monocytic cells. Cotreatment of cells with interferon-γ (IFN-γ) and lipolysaccharide (LPS) during T. gondii infection induced TNF-α production and decreased the number of parasitized cells (invasion index). Neutralization of the production of TNF-α using a specific monoclonal antibody or pentoxifylline enhanced the invasion index. The relationship between TNF-α production and protection of monocytic cells against T. gondii invasion was confirmed by treatment of infected cultures with exogenous TNF-α. Thus, in contrast to the results obtained in murine models but in accordance with those observed in other human models, the present study shows for the first time in human monocytic cells that T. gondii does not induce any TNF-α secretion and inhibits TNF-α production induced by IFN-γ/LPS. Received: 5 September 1999 / Accepted: 3 November 1999     

Serodiagnosis of acute toxoplasmosis using a recombinant form of the dense granule antigen GRA6 in an enzyme-linked immunosorbent assay

We developed an indirect enzyme-linked immunosorbent assay (ELISA) for the serological diagnosis of acute toxoplasmosis that used the recombinant granule antigen GRA6-GST as diagnostic antigen for the detection of IgG antibodies to Toxoplasma gondii in human sera. A total of 431 sera obtained from 336 patients with acute and chronic toxoplasmosis and from patients who were not infected with T. gondii were tested. Sera from patients with acute T. gondii infection, chronic infection, and no infection showed different absorbance values. For discrimination between the presence and the absence of acute toxoplasmosis the assay reached a specificity of 99.6%. Only one of the sera without significant anti-T. gondii. IgM antibodies showed a positive reaction to rGRA6-GST. The assay showed good intra- and interassay reproducibility (CV 6%/14%). We included a glutathione S-transferase (GST)-IgG enzyme immunoassay as a control assay in this study. Only 7 (4%) of 159 random sample sera reacted positively with GST. Received: 22 November 1997 / Accepted: 26 March 1998     

Immunogenic characterization of the chimeric surface antigen 1 and 2 (SAG1/2) of <Emphasis Type="Italic">Toxoplasma gondii</Emphasis> expressed in the yeast <Emphasis Type="Italic">Pichia pastoris</Emphasis>

In this study, we successfully expressed a chimerical surface antigen 1 and 2 (SAG1/2) of Toxoplasma gondii in Pichia pastoris. Eighty human serum samples, including 60 from confirmed cases of toxoplasmosis, were tested against the purified recombinant SAG1/2 in Western blots. Results of Western blots targeted at Toxoplasma IgG and IgM showed that the recombinant SAG1/2 reacted with all sera from the toxoplasmosis cases but none with the Toxoplasma-negative serum samples. These results showed that the P. pastoris-derived recombinant SAG1/2 was sensitive and specific and suitable for use as antigen for detecting anti-Toxoplasma antibodies. To further investigate the immunological characteristic of the recombinant protein, the recombinant SAG1/2 was injected subcutaneously into BALB/c mice, and their serum was tested against total protein lysate of T. gondii. Mice immunized with the recombinant SAG1/2 reacted specifically with the native SAG1 and SAG2 of T. gondii. Significant proliferation of splenocytes stimulated with tachyzoite total protein lysate was observed in vaccinated BALB/c mice but not in those from negative control mice. Specific production of IFN-γ, the Th1-type cytokines, was also found in stimulated splenocytes from vaccinated mice. These results show that the chimeric protein recombinant SAG1/2 can elicit a Th1-associated protection against T. gondii infections in mice. Finally, vaccinated mice were significantly protected against lethal challenge with live T. gondii RH strain tachyzoites (P < 0.005), and their survival time increased significantly compared to the negative control.     

Manipulation of mitogen-activated protein kinase/nuclear factor-κB-signaling cascades during intracellular Toxoplasma gondii infection

Summary: The intracellular protozoan Toxoplasma gondii exerts profound effects on nuclear factor‐κB (NF‐κB)‐ and mitogen‐activated protein kinase (MAPK)‐signaling cascades in macrophages. During early infection, nuclear translocation of NF‐κB is blocked, and later, the cells display defects in lipopolysaccharide (LPS)‐induced MAPK phosphorylation after undergoing initial activation in response to Toxoplasma itself. Infected macrophages that are subjected to triggering through Toll‐like receptor 4 (TLR4) with LPS display defective production of tumor necrosis factor‐α and IL‐12 (IL‐12) that likely reflects interference with NF‐κB‐ and MAPK‐signaling cascades. Nevertheless, T. gondii possesses molecules that themselves induce eventual proinflammatory cytokine synthesis. For interleukin‐12, this occurs through both myeloid differentiation factor 88‐dependent and chemokine receptor CCR5‐dependent pathways. The balance between activation and interference with proinflammatory signaling is likely to reflect the need to achieve an appropriate level of immunity that allows the host and parasite to maintain a stable interaction.     

A Proline‐Rich Polypeptide Complex (PRP) from Ovine Colostrum. Studies on the Effect of PRP on Nitric Oxide (NO) Production Induced by LPS in THP‐1 Cells

Abstract

A proline‐rich polypeptide complex (PRP) isolated from ovine colostrum shows immunoregulatory activity. Similar activity was observed when PRP was replaced with a nonapeptide (NP) isolated from chymotryptic digest of PRP. The polypeptide complex also shows procognitive activity. In the form of orally administered tablets called Colostrinin®, containing 100 µg of PRP, it improves the outcome of Alzheimer's disease (AD) patients. The mechanism of action of PRP/Colostrinin® in AD is not yet clarified. Microglial cells involvement in AD has been related to amyloid β (Aβ) internalization, the release of inflammatory cytokines, overproduction of nitrogen oxide (NO) and superoxide anion (O₂^?), and the development of neuritic plaques. It has been previously found in our laboratory that PRP regulates the secretion of an array of cytokines. It also was shown, in preliminary experiments using human blood cells and murine macrophages, that PRP inhibits production of NO and O₂^? induced by LPS. In the present work, to study the effect of PRP and NP on the release of NO and O₂^? induced by LPS we applied THP‐1 cells. The human monocyte/macrophage THP‐1 cell line has been widely used as a model of human microglial cells. The results obtained showed that THP‐1 cells release NO when activated with LPS. However, neither PRP nor NP induced production of NO. Although the nonapeptide, at higher concentration (100 µg/mL), showed an inhibitory activity on the release of NO induced by LPS, no inhibition was observed when PRP was used. THP‐1 cells treated with LPS, PRP or NP did not release O₂^?.     

Lack of macrophage migration inhibitory factor in mice does not affect hallmarks of the inflammatory/immune response during the first week after stroke

Background

Activation of glial cells, including astrocytes and microglia, has been implicated in the inflammatory responses underlying brain injury and neurodegenerative diseases including Alzheimer's and Parkinson's diseases. Although cultured astrocytes and microglia are capable of responding to pro-inflammatory cytokines and lipopolysaccharide (LPS) in the induction and release of inflammatory factors, no detailed analysis has been carried out to compare the induction of iNOS and sPLA2-IIA. In this study, we investigated the effects of cytokines (TNF-alpha, IL-1beta, and IFN-gamma) and LPS + IFN-gamma to induce temporal changes in cell morphology and induction of p-ERK1/2, iNOS and sPLA₂-IIA expression in immortalized rat (HAPI) and mouse (BV-2) microglial cells, immortalized rat astrocytes (DITNC), and primary microglia and astrocytes.

Methods/Results

Cytokines (TNF-alpha, IL-1beta, and IFN-gamma) and LPS + IFN-gamma induced a time-dependent increase in fine processes (filopodia) in microglial cells but not in astrocytes. Filopodia production was attributed to IFN-gamma and was dependent on ERK1/2 activation. Cytokines induced an early (15 min) and a delayed phase (1 ~ 4 h) increase in p-ERK1/2 expression in microglial cells, and the delayed phase increase corresponded to the increase in filopodia production. In general, microglial cells are more active in responding to cytokines and LPS than astrocytes in the induction of NO. Although IFN-gamma and LPS could individually induce NO, additive production was observed when IFN-gamma was added together with LPS. On the other hand, while TNF-alpha, IL-1beta, and LPS could individually induce sPLA₂-IIA mRNA and protein expression, this induction process does not require IFN-gamma. Interestingly, neither rat immortalized nor primary microglial cells were capable of responding to cytokines and LPS in the induction of sPLA2-IIA expression.

Conclusion

These results demonstrated the utility of BV-2 and HAPI cells as models for investigation on cytokine and LPS induction of iNOS, and DITNC astrocytes for induction of sPLA2-IIA. In addition, results further demonstrated that cytokine-induced sPLA2-IIA is attributed mainly to astrocytes and not microglial cells.     

The PI3K/Akt pathway is required for LPS activation of microglial cells

Upregulation of inflammatory responses in the brain is associated with a number of neurodegenerative diseases. Microglia are activated in neurodegenerative diseases, producing pro-inflammatory mediators. Critically, lipopolysaccharide (LPS)-induced microglial activation causes dopaminergic neurodegeneration in vitro and in vivo. The signaling mechanisms triggered by LPS to stimulate the release of pro-inflammatory mediators in microglial cells are still incompletely understood. To further explore the mechanisms of LPS-mediated inflammatory response of microglial cells, we studied the role of phosphatidylinositol 3-kinase (PI3K)/Akt signal transduction pathways known to be activated by toll-like receptor-4 signaling through LPS. In the current study, we report that the activation profile of LPS-induced pAkt activation preceded those of LPS-induced NF-κB activation, suggesting a role for PI3K/Akt in the pathway activation of NF-κB-dependent inflammatory responses of activated microglia. These results, providing the first evidence that PI3K dependent signaling is involved in the inflammatory responses of microglial cells following LPS stimulation, may be useful in preventing inflammatory based neurodegenerative processes.     

T cell Suppression In Vitro During Toxoplasma gondii Infection is the Result of IL‐2 Competition Between Tregs and T cells Leading to Death of Proliferating T cells

A reduced proliferation to T cell mitogens is observed in vitro in murine cells isolated during the acute phase of Toxoplasma gondii infection. Foxp3⁺ regulatory T cells (Tregs) mediate this suppression, which is interleukin (IL)‐2 dependent. In this work, we analysed the mechanism of this Treg‐mediated suppression. We found that removal of antigen‐presenting cells (APC) from spleen cells from infected mice did not modify suppression but further elimination of Tregs led to a restored proliferation, demonstrating that Tregs mediate suppression in the absence of APC. Production of IL‐2 by T cells from infected animals was abolished but partially restored when Tregs were removed. However, IL‐2 levels and T cell proliferation were restored when Tregs and T cells were separated by transwells, indicating that Tregs require close proximity with T cells to induce suppression. Tregs from infected mice were able to reduce proliferation of CTLL‐2 cells in the classical IL‐2 bioassay, strongly suggesting that Tregs compete with T cells for IL‐2. We found that T cells from infected mice died after a few rounds of division in vitro, but addition of recombinant IL‐2 or removal of Tregs abolished this effect. Our results showed that suppression of T cell proliferation during acute Toxoplasma gondii infection is the result of death of proliferating T cells by Treg‐mediated IL‐2 competition. Thus, immunosuppression is due to death of proliferating T cells as a consequence of low IL‐2 availability.     

Pretreatment with lipopolysaccharide ameliorates Pseudomonas exotoxin A-induced hepatotoxicity in rats

Abstract

Context: Liver injury can be induced by various hepatotoxicants, including Pseudomonas aeruginosa exotoxin A (PEA). Our previous study indicated that PEA-induced rat hepatotoxicity was T cells and Kupffer cells dependent. Several reports have demonstrated that non-toxic doses of bacterial lipopolysaccharide (LPS) can protect liver against the chemicals-induced toxicity such as acetaminophen and concanavalin-A.

Objective: This study aimed to investigate the protecting mechanisms of LPS on PEA-induced hepatotoxicity.

Results: Rats pretreated with LPS (40?μg/kg, 12?h before PEA admission) significantly decreased animal mortality, serum enzyme (ALT, AST and T-bil) activities, histopathological changes and hepatocytes apoptosis following challenge with PEA. The concentrations of tumor necrosis factor-alpha (TNF-α), interferon-gamma (IFN-γ) and interleukin-2 (IL-2) were reduced, but IL-6 and IL-10 were increased in the serum. In addition, prior treatment of these LPS-pretreated rats with gadolinium chloride (GdCl₃), a selective Kupffer cell depletion agent, markedly enhanced liver injury after PEA administration. In contrast, the pretreatment of LPS to T-cell deficient athymic nude rats still display significant attenuation of PEA-induced liver injury. This observation further confirmed our hypothesis that LPS ameliorate PEA-hepatotoxicity was through Kupffer cells but not T cells. Moreover, LPS-induced hepatoprotection ability was neutralized by co-treatment with anti-TNF-α antibodies, but not with anti-IFN-γ antibodies. Finally, replacement of LPS with RS-LPS (Rhodobacter sphaeroides LPS), a Toll like receptor-4 (TLR-4) antagonist, resulted in severe hepatotoxicity.

Conclusion: These results suggested that Kupffer cells, TNF-α and TLR-4 play central mediator roles during the hepatoprotection against PEA-induced hepatotoxicity conferred by LPS.     

Dectin-1-CD37 association regulates IL-6 expression during Toxoplasma gondii infection

Toxoplasma gondii can establish chronic infection and is characterized by the formation of tissue cysts in the brain. Although T. gondii can infect any kind of nucleated cells, macrophages and related mononuclear phagocytes are its preferred targets in vivo. Microglial cells are the resident macrophages in the central nervous system. It has been reported that CD37, a tetraspanin molecule, is expressed exclusively in the immune system; Dectin-1, an important pattern-recognition receptor, is expressed on the surface of murine primary microglia. The Dectin-1-CD37 association can affect Dectin-1-mediated IL-6 secretion. However, there is no report concerning the relationship among the expressions of Dectin-1, IL-6, and CD37 during T. gondii infection. In the present study, Kunming outbred mice were infected with Prugniaud (Pru), a type II strain of T. gondii by oral gavage, and BV-2 murine microglial cells were cocultured with RH tachyzoites of T. gondii. By H&E and immunohistochemical staining, the results showed that marked inflammation and a significantly increased activation of Iba1-positive microglial cells were observed in the brain tissues of mice infected with T. gondii Pru strain at 5 weeks postinfection (p.i.) in comparison of uninfected controls. Using quantitative real-time PCR detection, Dectin-1 messenger RNA (mRNA) expressions were significantly upregulated in both brains at 3 (P?<?0.01), 5 (P?<?0.01), 7 (P?<?0.01), and 9 (P?<?0.05) weeks p.i. and spleens at 3, 5, 7, and 9 weeks p.i. (P?<?0.01). IL-6 expressions showed similar dynamic tendency as that of Dectin-1 in both the brains and spleens at the same times in comparison of uninfected controls; CD37 expressions were significantly increased in the brain tissues at all the times (P?<?0.01) and no significant differences in the spleens at 3 weeks p.i. but significantly downregulated in the spleens at 5, 7, and 9 weeks p.i. (P?<?0.01). In vitro study showed that compared with uninfected controls, the mRNA expressions of Dectin-1 at 2, 4, 8, and 10 h (P?<?0.01); IL-6 at 8 and 10 h (P?<?0.01); and CD37 at 4 (P?<?0.05), 8 (P?<?0.01), and 10 h (P?<?0.01) were significantly upregulated in BV-2 murine microglial cells stimulated with RH tachyzoites of T. gondii. Our data suggested that the expression of Dectin-1 was positively correlated with that of IL-6 in toxoplasmic encephalitis (TE) mouse model; Dectin-1 interaction with tetraspanin CD37 regulated IL-6 expression in both the brain tissues of TE mouse model and in the T. gongdii-infected BV-2 murine microglial cells.     

Effect of IFN-gamma on the proliferation of Toxoplasma gondii in monocytes and monocyte-derived macrophages from AIDS patients.

This study was undertaken to determine whether the activity of monocytes and monocyte-derived macrophages (MDM) from acquired immune deficiency syndrome (AIDS) patients against Toxoplasma gondii is altered and whether this activity can be modulated by recombinant interferon-gamma (rIFN-gamma). Untreated and rIFN-gamma-treated monocytes or MDM from AIDS patients and from healthy controls were infected with T. gondii and the proliferation of these protozoa was determined. The H2O2 release by monocytes from AIDS patients and healthy controls was measured upon stimulation with phorbol myristate acetate (PMA) and formyl methionyl leucyl phenylalanine (FMLP). Monocytes from AIDS patients exhibited significantly lower toxoplasmastic activity compared to monocytes from healthy controls. The H2O2 release by monocytes from AIDS patients was also diminished. Incubation of monocytes from AIDS patients with rIFN-gamma for 2 days, but not 1 day, restored their toxoplasmastatic activity. The rate of proliferation of T. gondii was higher in MDM from AIDS patients than in MDM from healthy controls. Treatment of MDM from AIDS patients with rIFN-gamma for 1, 2 or 3 days resulted in partial inhibition of the proliferation of T. gondii. Collectively, these results demonstrate that the reduced toxoplasmastatic activity of monocytes and MDM from AIDS patients can be enhanced by in vitro treatment with rIFN-gamma, which supports the clinical use of rIFN-gamma for the treatment of opportunistic infections in these patients.