Induction of heat shock protein closely correlates with protection against Toxoplasma gondii infection

CD40 in Endothelial Cells Restricts Neural Tissue Invasion by Toxoplasma gondii

Little is known about whether pathogen invasion of neural tissue is affected by immune-based mechanisms in endothelial cells. We examined the effects of endothelial cell CD40 on Toxoplasma gondii invasion of the retina and brain, organs seeded hematogenously. T. gondii circulates in the bloodstream within infected leukocytes (including monocytes and dendritic cells) and as extracellular tachyzoites. After T. gondii infection, mice that expressed CD40 restricted to endothelial cells exhibited diminished parasite loads and histopathology in the retina and brain. These mice also had lower parasite loads in the retina and brain after intravenous (i.v.) injection of infected monocytes or dendritic cells. The protective effect of endothelial cell CD40 was not explained by changes in cellular or humoral immunity, reduced transmigration of leukocytes into neural tissue, or reduced invasion by extracellular parasites. Circulating T. gondii-infected leukocytes (dendritic cells used as a model) led to infection of neural endothelial cells. The number of foci of infection in these cells were reduced if endothelial cells expressed CD40. Infected dendritic cells and macrophages expressed membrane-associated inducible Hsp70. Infected leukocytes triggered Hsp70-dependent autophagy in CD40⁺ endothelial cells and anti-T. gondii activity dependent on ULK1 and beclin 1. Reduced parasite load in the retina and brain not only required CD40 expression in endothelial cells but was also dependent on beclin 1 and the expression of inducible Hsp70 in dendritic cells. These studies suggest that during endothelial cell-leukocyte interaction, CD40 restricts T. gondii invasion of neural tissue through a mechanism that appears mediated by endothelial cell anti-parasitic activity stimulated by Hsp70.

Trypanosoma brucei brucei: A comparison of gene expression in the liver and spleen of infected mice utilizing cDNA microarray technology

Trypanosoma brucei brucei, the infectious agent of the disease known as Nagana, is a pathogenic trypanosome occurring in Africa, where it causes significant economic loss to domesticated livestock. Although many studies on the histopathology of organs of mice infected with T. b. brucei have been reported, little work has been done regarding gene expression in these organs in infected mice. In this paper, we describe the use of cDNA microarray to determine gene expression profiles in the liver and spleen of mice infected with T. b. brucei (STIB 920) at peak parasitaemia (12 days after infection). Our results showed that a total of 123 genes in the liver and 389 genes in the spleen were expressed differentially in T. b. brucei infected mice. In contrast, however, in an acute infection in mice caused by Trypanosoma brucei evansi, a species genetically related to T. b. brucei, 336 genes in the liver and 190 genes in the spleen were expressed, differentially, indicating that the liver of mice was more affected by the acute T. b. evansi infection whilst the spleen was more affected by the subacute T. b. brucei infection. Our results provide a number of possible reasons why mice infected with T. b. evansi die sooner than those infected with T. b. brucei: (1) mice infected with T. b. evansi may need more stress response proteins to help them pass through the infection and these are probably excessively consumed; (2) proliferating cell nuclear antigen was more down-regulated in the liver of mice infected with T. b. evansi, which indicated that the inhibition of proliferation of hepatocytes in mice infected with T. b. evansi might be more severe than that in T. b. brucei infection; and (3) more hepatocyte apoptosis occurred in the mice infected with T. b. evansi and this might be probably the most important reason why mice died sooner than those infected with T. b. brucei. Studies of the changes in the gene expression profile in the liver and spleen of mice infected with T. b. brucei may be helpful in understanding the mechanisms of pathogenesis in Nagana disease at the molecular level. By comparing the gene profiles of the liver and spleen of mice infected with T. b. brucei with T. b. evansi, we have identified a number of factors that could explain the differences in pathogenesis in mice infected with these two African trypanosomes.

Analysis of gene expression profiles in the liver and spleen of mice infected with Trypanosoma evansi by using a cDNA microarray

Trypanosoma evansi, the cause of the disease Surra in livestock, is the most widely geographically distributed pathogenic trypanosome occurring in Africa, South and Central America, and Asia, where it causes significant economic loss. Although many studies have described the histopathology induced in the organs of mice infected with T. evansi, few studies have been conducted on gene expression in these organs. Here we used complementary DNA microarray to analyze the gene expression profiles in the liver and spleen of mice infected with T. evansi (STIB 806) at the peak parasitemia (7 days after infection). A total of 14,000 sequences including full length and partial complementary DNAs representing novel, known, and control genes of mouse were analyzed. Results from GeneOntology annotation showed that 158 genes in the liver and 73 genes in the spleen were up-regulated in the infected mice and that 178 genes in the liver and 117 genes in the spleen of infected mice were down-regulated compared with control (non-infected) mice. Most of these genes are metabolism, transport, protein biosynthesis, transcription factors, and nucleic acid binding protein-related genes. The changes of some important genes, such as heat shock protein 70 and proliferating cell nuclear antigen, were confirmed by quantitative reverse transcriptase polymerase chain reaction and immunohistochemistry. TdT-mediated dUTP-digoxigenin nick end labeling analysis results revealed that extensive apoptosis occurred in the liver of infected mice at the peak of parasitemia. Our results provide a comprehensive profile of changes in gene expression in the liver and spleen of mice infected with T. evansi and may be helpful in understanding the pathogenesis of Surra at a molecular level.

The immunology of parasite infections in immunocompromised hosts

Immune compromise can modify the severity and manifestation of some parasitic infections. More widespread use of newer immnosuppressive therapies, the growing population of individuals with immunocompromised states as well as the prolonged survival of these patients have altered the pattern of parasitic infection. This review article discusses the burden and immunology of parasitic infections in patients who are immunocompromised secondary to congenital immunodeficiency, malnutrition, malignancy, and immunosuppressive medications. This review does not address the literature on parasitic infections in the setting of HIV-1 infection.

The involvement of immunoproteasomes in induction of MHC class I-restricted immunity targeting Toxoplasma SAG1

The ubiquitin-proteasome system (UPS) plays an indispensable role in inducing MHC class I-restricted CD8+ T cells and was exploited in the development of a DNA vaccine against the intracellular protozoan Toxoplasma gondii by constructing a chimeric DNA encoding a fusion protein between murine ubiquitin and the toxoplasma antigen SAG1. The SAG1 peptide was promptly degraded in antigen-presenting cells (APCs) transfected with the chimeric DNA. Degradation, however, was hampered by incubating the APCs with the proteasome inhibitor epoxomicin. Mice vaccinated with the DNA acquired potent protective immunity mediated by MHC class I-restricted CD8+ T cells against infection by the highly virulent Toxoplasma. The accelerated degradation and induction of immunity were dependent on the UPS since mice lacking an immuno-subunit of 20S proteasome, LMP7, lost these functions, although they were independent of the proteasome regulator PA28alpha/beta complex.

Roles of NKT cells in resistance against infection with Toxoplasma gondii and in expression of heat shock protein 65 in the host macrophages

We investigated the roles of gamma delta T, NK, and NK1.1(+) T-like (NKT) cells in protective immunity against infection with Toxoplasma gondii. gamma delta T cells, NKT and NK cells, and NK cells in BALB/c mice were depleted by treatment with anti-TCR-gamma delta monoclonal antibody (mAb), anti-interleukin-2 receptor beta chain (IL-2R beta) mAb, and anti-asialoGM1 Ab, respectively, and these mice were infected with T. gondii. Treatment of mice with anti-TCR-gamma delta mAb aggravated toxoplasmosis, while treatment with anti-asialoGM1 Ab had no effects. Treatment with anti-IL-2R beta mAb enhanced the expression of heat shock protein 65 (HSP65) and gamma interferon (IFN-gamma) mRNA, while it inhibited interleukin-4 (IL-4) mRNA expression, ameliorating toxoplasmosis. In addition to NK cells, anti-IL-2R beta mAb eliminated cells expressing IL-2R beta and intermediate levels of CD3 (IL-2R beta(+) CD3(int)). Mice treated with anti-IL-2R beta mAb decreased the number of DX5(+) CD3(int) cells, which are considered to be equivalent to NK1.1(+)T cells in NK1.1 allele-negative strains. IL-2R beta(+) CD3(int) cells isolated from splenic and hepatic lymphoid cells were confirmed to express the TCR-V alpha 14 transcript. The magnitude of HSP65 induction in macrophages correlated with the protective potential against T. gondii infection after treatment with the antibodies, supporting our previous finding that gamma delta T cells play an essential role in the induction of HSP65 in host macrophages. Interestingly, NKT cells suppressed the expression of gamma delta T cell-induced HSP65 and IFN-gamma. Furthermore, depletion of IL-2R beta(+) CD3(int) cells suppressed the IL-4 mRNA expression. These results suggest that NKT cells may be the cells responsible for suppression of protective immunity against T. gondii infection by interfering with the gamma delta T cell-induced HSP65 expression, possibly through the generation of IL-4.

Granule-dependent killing of Toxoplasma gondii by CD8+ T cells

Immunization of mice with live bradyzoites of a low-virulent Beverley strain of Toxoplasma gondii has been shown to increase CD8+ T-cell mediated immunity against a highly virulent RH strain. We found that preimmunization with an RH homogenate further enhanced this immunity. Using this model, we investigated the mechanism of CD8+ T-cell mediated protection against T. gondii infection. Splenic cells from mice immunized with RH homogenate and live bradyzoites stimulated apoptosis of RH-infected J774A.1 macrophages in vitro, and at the same time, the immunization significantly suppressed the proliferation of parasites within macrophages, as assessed by measuring 3H-uracil uptake by the parasites. Splenic cells from the immunized mice produced larger amounts of interferon-gamma (IFN-gamma) than did naive splenic cells; however, the production of nitric oxide (NO) by RH-infected macrophages was not enhanced. The elimination of CD8+ T cells from splenic cells significantly reduced their inhibitory action on parasite proliferation as well as their cytotoxic activity against RH-infected macrophages, but it did not affect the production of IFN-gamma. Treatment of CD8+ T-enriched splenic cells from the immunized mice with concanamycin A, but not an anti-Fas ligand monoclonal antibody, significantly reduced their anti-proliferative and killing capabilities, suggesting that the CD8+ T cells induced by immunization with RH antigen and live bradyzoites of the Beverley strain may exert protection against T. gondii infection at least in part through granule-dependent cytotoxic activities.

CD4+ T cells are required for HSP65 expression in host macrophages and for protection of mice infected with Plasmodium yoelii

We have reported that macrophages expressing heat-shock protein 65 play an essential role in protection of mice infected with Plasmodium yoelii. In this study, we investigated the function and expression mechanism of HSP65 in macrophages of mice infected with P. yoelii. C57BL/6 (B6) mice are susceptible to infection with the lethal (L) strain but resistant to infection with the non-lethal (NL) strain of P. yoelii. The percentage of apoptotic macrophages in mice infected with the L strain was higher than that in mice infected with the NL strain. However, the percentage was low in L strain infected mice if they acquired resistance to the infection by primary infection with the NL strain. That apoptosis was reversely correlated with HSP65 expression in splenic macrophages from mice infected with P. yoelii suggests HSP65 may contribute to protective immunity by preventing apoptosis of macrophages in malarial infection. Cell depletion/transfer experiments showed that CD4+ T cells, but not CD8+ T cells, gammadelta T cells, NK cells or NK T cells, were required for HSP65 expression in macrophages as well as for protection of mice infected with P. yoelii. In conclusion, HSP65 may play a role in preventing apoptosis of macrophages in mice infected with P. yoelii. CD4+ T cells are required for HSP65 expression and for protective immunity against P. yoelii infection.

Macrophages expressing heat-shock protein 65 play an essential role in protection of mice infected with Plasmodium yoelii

C57BL/6 (B6) mice are resistant to infection with the non-lethal (NL) strain of Plasmodium yoelii 17X, while being susceptible to that with the lethal (L) strain. The 65 000 MW heat-shock protein (hsp 65) was strongly expressed in splenic adherent cells of B6 mice 10 days after infection with the NL strain of P. yoelii but only slightly in those from mice infected with the L strain. Mice which had survived infection with the NL strain were resistant to challenge with the L strain and hsp 65 was strongly expressed in splenic adherent cells of these mice. Severe combined immunodeficient mice and nude mice were susceptible to malaria infection even with the NL strain and did not express hsp 65 after infection, suggesting that T cells are required for the expression of hsp 65 as well as for protective immunity. B6 mice treated intraperitoneally with carrageenan, which impairs the macrophage function, became susceptible to NL strain infection, indicating that macrophages play an important role as the final effectors in protective immunity. These results demonstrate that the hsp 65 expressed by macrophages correlates closely with protection against P. yoelii infection.

Expression and role of heat-shock protein 65 (HSP65) in macrophages during Trypanosoma cruzi infection: involvement of HSP65 in prevention of apoptosis of macrophages

The 65-kDa heat-shock protein (HSP65) is thought to play a role in host defense against infections with various microbial pathogens and in autoimmune inflammatory disorders. We investigated the biological function and expression mechanism of HSP65 in macrophages of mice infected with Trypanosoma cruzi. BALB/c mice, which are susceptible to T. cruzi, showed high levels of parasitemia, and 80% of these mice died within 42 days after the infection, whereas resistant C57BL/6 or DBA/2 mice showed low levels of transient parasitemia and all survived. HSP65 expression was correlated with resistance to T. cruzi infection; HSP65 was more strongly expressed in macrophages of resistant C57BL/6 and DBA/2 mice than in macrophages of susceptible BALB/c mice. Immunodeficient BALB/c-nu/nu (nude) and C.B-17 scid/scid (SCID) mice were shown to be highly susceptible to this infection, and they did not express detectable levels of HSP65, suggesting that T cells play essential roles in the expression of HSP65 as well as in protective immunity against the infection. CD4(+) T cells, but not CD8(+) T cells or gammadelta T cells, were the cell population responsible for the induction of HSP65 expression in macrophages. Furthermore, depletion of asialo GM-1(+) NK cells made resistant C57BL/6 mice more susceptible to the infection, and HSP65 expression in their macrophages was abolished. Semiquantitative reverse transcription PCR analyses showed that both interferon gamma (IFN-gamma) and tumor necrosis factor alpha (TNF-alpha) mRNA levels in CD4(+) T cells became low when resistant C57BL/6 mice were depleted of NK cells, suggesting that NK cells contribute to functional differentiation of CD4(+) T cells and thereby affect the induction of HSP65 expression. To determine the function of HSP65, macrophages were treated in vitro with antisense oligonucleotide for HSP65 prior to inducing HSP65 with IFN-gamma plus TNF-alpha or T. cruzi infection. This treatment did not affect the production of nitric oxide following activation, but the treated macrophages became susceptible to apoptosis. These results indicate that HSP65 plays a role in preventing the apoptosis of macrophages and thereby contributes to host resistance against T. cruzi infection.

Regulation and function of T-cell-mediated immunity during Toxoplasma gondii infection

The intracellular protozoan Toxoplasma gondii is a widespread opportunistic parasite of humans and animals. Normally, T. gondii establishes itself within brain and skeletal muscle tissues, persisting for the life of the host. Initiating and sustaining strong T-cell-mediated immunity is crucial in preventing the emergence of T. gondii as a serious pathogen. The parasite induces high levels of gamma interferon (IFN-gamma) during initial infection as a result of early T-cell as well as natural killer (NK) cell activation. Induction of interleukin-12 by macrophages is a major mechanism driving early IFN-gamma synthesis. The latter cytokine, in addition to promoting the differentiation of Th1 effectors, is important in macrophage activation and acquisition of microbicidal functions, such as nitric oxide release. During chronic infection, parasite-specific T lymphocytes release high levels of IFN-gamma, which is required to prevent cyst reactivation. T-cell-mediated cytolytic activity against infected cells, while easily demonstrable, plays a secondary role to inflammatory cytokine production. While part of the clinical manifestations of toxoplasmosis results from direct tissue destruction by the parasite, inflammatory cytokine-mediated immunopathologic changes may also contribute to disease progression.

The role of host-derived heat-shock protein in immunity against Toxoplasma gondii infection

Heat-shock proteins (HSPs) are evolutionarily highly conserved polypeptides synthesized by cells to preserve cellular functions under a variety of stressful conditions, including infections. In infections, both host cells and pathogens express HSPs, although the role of these molecules in the host-pathogen relationship is elusive. Here, Hajime Hisaeda and Kunisuke Himeno show that a correlation exists between the 65 kDa HSP molecule (HSP65) and protection against Toxoplasma gondii infection, suggesting that this protein contributes to the host defense system. These findings may help in the understanding of the complicated host-parasite relationship.

Contribution of 65-kDa heat shock protein induced by gamma and delta T cells to protection against Toxoplasma gondii infection

Heat shock proteins (HSPs) are evolutionarily highly conserved polypeptides synthesized by many cells to preserve cellular functions under a variety of stressful conditions including infections. We have investigated the involvement of 65-kDa HSP (HSP65) in host protection against an intracellular protozoan parasite, Toxoplasma gondii, in mice. Experiments using low and highly virulent strains of Tox. gondii revealed that induction of murine HSP65 on macrophages closely correlates with protection against infection with this protozoan. Furthermore, we clarified that T cells, especially gamma delta T cells, are indispensable for HSP65 expression. A similar relationship between the expression of HSP65 on host macrophages and protective immunity was observed in mice infected with Leishmania major and Trypanosoma cruzi, both of which are obligate intracellular protozoa as is Tox. gondii.

Contribution of extrathymic gamma delta T cells to the expression of heat-shock protein and to protective immunity in mice infected with Toxoplasma gondii

We demonstrated that gamma delta T cells contribute to protective immunity against Toxoplasma gondii by inducing the expression of a 65,000 MW heat-shock protein (hsp 65) in host macrophages. Here we examined the role of extrathymic and intrathymic gamma delta T cells in protective immunity and hsp 65 expression in mice infected with T. gondii. Intrathymic gamma delta T cells were obtained from severe combined immunodeficiency (SCID) mice grafted with syngeneic fetal thymus (TG-SCID), in which only T cells derived from the donor thymus developed, whereas extrathymic gamma delta T cells were obtained from nude mice that lack thymus. Extrathymic gamma delta T cells from T. gondii-infected nude mice differed from intrathymic gamma delta T cells of infected TG-SCID mice, in terms of Thy1.2 expression and V-region gene usage of T-cell receptor (TCR) gamma delta. Extrathymic gamma delta T cells expressed extremely high levels of Thy1.2, and had V gamma 7 repertoire but lacked V gamma 5,6 and V delta 1,5. On the other hand, intrathymic gamma delta T cells express intermediate and low levels of Thy1,2. These cells possessed V gamma 5,6 and V delta 1,5 but failed to rearrange the V gamma 7 gene. Peritoneal macrophages from infected nude mice contained hsp 65, whereas this protein was scarcely expressed in those of infected TG-SCID mice. Transfer of extrathymic, but not of intrathymic gamma delta T cells to SCID mice enabled their macrophages to express hsp 65. Athymic nude mice were significantly resistant to the infection compared with SCID mice which lack gamma delta T as well as alpha beta T cells. The resistance was dependent upon extrathymic gamma delta T cells, since nude mice depleted of gamma delta T cells using a corresponding monoclonal antibody became extremely susceptible. These results indicated that extrathymic rather than intrathymic gamma delta T cells play some crucial roles in protection against T. gondii and in hsp 65 expression.

Mycobacterial 65-kilodalton heat shock protein induces tumor necrosis factor alpha and interleukin 6, reactive nitrogen intermediates, and toxoplasmastatic activity in murine peritoneal macrophages

The 65-kDa heat shock protein (Hsp65) is supposed to play a role in host defense against infections with various microbial pathogens and in autoimmune inflammatory disorders. These effects are thought to result mainly from an Hsp65-specific T-lymphocyte-mediated immune response that recognizes conserved epitopes. The aim of the present study was to assess whether mycobacterial Hsp65 has a direct effect on resident murine peritoneal macrophages, independent of Hsp65-sensitized T lymphocytes. Exposure of peritoneal macrophages from naive C57BL/6 mice to the mycobacterial Hsp65 in vitro induced an enhanced release of tumor necrosis factor alpha (TNF-alpha) and interleukin 6. These cells also produced large amounts of reactive nitrogen intermediates (RNI) and inhibited the intracellular proliferation of Toxoplasma gondii. Small amounts of gamma interferon acted synergistically with Hsp65. Thus, exposure of murine macrophages to Hsp65 results in activation of these cells. The acquisition of these characteristics by peritoneal macrophages occurred in the absence of sensitized T lymphocytes. Addition of anti-TNF-alpha antiserum resulted in an attenuation of the Hsp65-induced release of RNI and toxoplasmastatic activity, indicating that endogenous TNF-alpha is involved in the Hsp65-induced macrophage activation. The conclusion of this study is that in vitro exposure of peritoneal macrophages to the mycobacterial Hsp65 induces the release of proinflammatory cytokines and RNI and results in inhibition of the intracellular proliferation of T. gondii. These effects on murine macrophages occur independently of Hsp65-specific T lymphocytes. The proinflammatory effect of Hsp65 demonstrated in this study suggests that this heat shock protein may play a role in the initiation of inflammation that adds to a non-species-specific resistance in the early stages of infections.

Preferential activation and expansion of human peripheral blood gamma delta T cells in response to Toxoplasma gondii in vitro and their cytokine production and cytotoxic activity against T. gondii-infected cells

Studies were conducted to determine if gamma delta T cells participate in the immune response to Toxoplasma gondii. Preferential expansion of human gamma delta T cells occurred when peripheral blood T cells from either T. gondii-seronegative or seropositive individuals were incubated with autologous PBMC infected with the parasite. That gamma delta T cells proliferated after incubation with infected cells was confirmed using purified of gamma delta T cells. These T. gondii-induced gamma delta T cell responses did not require prior exposure to the parasite since T cells obtained from umbilical cord blood from seronegative newborns also exhibited preferential expansion of gamma delta T cells. Cytofluorometric analysis of T cells obtained from either umbilical cord blood or peripheral blood from adults revealed that V gamma 9+ and V delta 2+ gamma delta T cells responded to stimulation with infected cells. Preferential expansion of gamma delta T cells was not restricted by polymorphic determinants of MHC molecules. PBMC that had internalized killed parasites but not PBMC incubated with T. gondii lysate antigens also stimulated preferential expansion and activation of gamma delta T cells as assessed by expression of CD25 and HLA-DR molecules. V gamma 9+V delta 2+ gamma delta T cells were cytotoxic for T. gondii-infected cells in an MHC-unrestricted manner, and produced IFN-gamma, IL-2, TNF-alpha, but not IL-4 when incubated with cells infected with the parasite. These results suggest that rapid induction of a remarkable primary gamma delta T cell response may be important in the early protective immune response to T. gondii.

Heat shock proteins of Toxoplasma gondii

We have investigated heat shock protein (HSP) expression in mouse-virulent and -avirulent strains of Toxoplasma gondii by performing Western blot analysis using a monoclonal antibody against HSP65 of Mycobacterium bovis and a polyclonal antiserum against HSP70 of Plasmodium falciparum as primary antibodies. We initially observed that murine macrophages express HSP65 when infected with either virulent or avirulent strains, a result which contradicts previous reports. Differential HSP expression consistent which virulence was observed between strains, with high levels of a 70kDa HSP (HSP70) only detected in virulent strains in vivo. This protein was not observed in virulent strains in the immunocompromised mouse or in vitro, suggesting induction by immunological stress. This protein was only poorly expressed in avirulent strains. A 65kDa protein was observed in all strains in vivo and in vitro, suggesting a shared epitope with HSP70. These results are consistent with the hypothesis that the induced expression of HSP70 in virulent strains of T. gondii by immunological stresses may provide protection for these strains against cell damage associated with invasion of the host, allowing the virulent strains to persist as tachyzoites without the requirement for the encystation observed in avirulent strains.

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.

Expression of 65- and 67-kilodalton heat-regulated proteins and a 70-kilodalton heat shock cognate protein of Leishmania donovani in macrophages

Heat shock protein (HSP) expression was examined in murine bone marrow-derived macrophages infected with stationary-phase promastigotes of Leishmania donovani. Immunoblotting performed with a rabbit polyclonal antiserum raised against HSP60 from Heliothis virescens (moth) revealed the de novo appearance of 65- and 67-kDa proteins in leishmania-infected macrophages. A third protein of 60 kDa, which represented murine HSP60, was also detected, and its expression did not change in response to infection. In contrast, expression of the novel 65- and 67-kDa proteins in infected cells was coordinately regulated and, at 24 h of infection, reached maximal levels of 52 to 100% increases above initial levels determined at 3 h. Proteins which had identical electrophoretic mobilities and were similarly regulated in response to heat were also detected in promastigotes. The appearance of these proteins in macrophages was specific to leishmania infection in that neither protein was detected in noninfected cells either in the basal state or following several treatments, including (i) infection with Yersinia pseudotuberculosis, (ii) phagocytosis of Staphylococcus aureus, (iii) NaAsO2 treatment, and (iv) heat shock. Expression of the 65- and 67-kDa heat-regulated Leishmania proteins was also observed to be selective, in that as their concentration was increasing, the abundance of the Leishmania surface protease gp63 in infected cells was noted to decrease. Murine HSP60 but not the Leishmania heat-regulated proteins was also recognized by a distinct rabbit antiserum raised against human HSP60, suggesting the presence of specific determinants within these Leishmania proteins. A monoclonal antibody that recognizes both mammalian HSP70 and HSP70 from plasmodia detected single isoforms of both Leishmania and murine HSP70 in infected cells, and the level of neither protein changed during infection. Moreover, although a murine HSP of 73 kDa was induced in response to both heat shock and NaAsO2 treatment, it was not induced to detectable levels by infection. The rapid and relatively high level of expression of inducible HSP60-related proteins of L. donovani and Leishmania HSP70 in infected macrophages suggests that these proteins are involved in pathogenesis and may be important targets of the immune response.

Murine peritoneal macrophages activated by the mycobacterial 65-kilodalton heat shock protein express enhanced microbicidal activity in vitro

After an intraperitoneal (i.p.) injection of purified protein derivative, peritoneal macrophages from mice infected with Mycobacterium bovis bacillus Calmette-Guérin (BCG) show an enhanced respiratory burst, inhibit the intracellular proliferation of Toxoplasma gondii, and kill Listeria monocytogenes more efficiently than peritoneal macrophages from normal mice. One of the immunodominant antigens of Mycobacterium spp. is the 65-kDa heat shock protein (Hsp 65), and in the present study, we determined whether injection of this protein into mice leads to activation of their peritoneal macrophages. After an i.p. injection of Hsp 65, peritoneal macrophages from BCG-infected CBA/J mice also released more H2O2, inhibited the proliferation of T. gondii, and killed L. monocytogenes faster than peritoneal macrophages from normal mice, although Hsp 65 was less effective than purified protein derivative. When normal mice were injected with Hsp 65 suspended in saline after a booster injection with Hsp 65, their macrophages did not display enhanced antimicrobial activity, indicating that an adjuvant was required for a cellular immune response against Hsp 65. In the present study, the adjuvant dimethyl dioctadecylammonium bromide (DDA) was preferred because it contains no endotoxin or mycobacterial antigens and because it has been reported that DDA does not induce the production of gamma interferon. Peritoneal macrophages from C57BL/6 and CBA/J mice that had received a subcutaneous injection of Hsp 65 suspended in DDA followed by an i.p. booster injection of Hsp 65 suspended in saline were activated, as indicated by the enhanced production of H2O2, inhibition of the intracellular proliferation of T. gondii, and increased rate of intracellular killing of L. monocytogenes in vitro relative to that by resident peritoneal macrophages and peritoneal macrophages obtained from mice that had received ovalbumin instead of Hsp 65. The rate of phagocytosis of L. monocytogenes was not affected by Hsp 65 treatment. Despite the in vitro expression of enhanced microbicidal activity of peritoneal macrophages, no difference in the growth of L. monocytogenes in the liver and spleen between Hsp 65-treated and control mice was found.