Resistance to apoptosis in HIV-infected CD4+ T lymphocytes is mediated by macrophages: role for Nef and immune activation in viral persistence

Apoptosis or programmed cell death may play a critical role in AIDS pathogenesis through depletion of both CD4(+) and CD8(+) T lymphocytes. Using a reporter virus, a recombinant HIV infectious clone expressing the green fluorescent protein (GFP), apoptosis was measured in productively infected CD4(+) T lymphocytes, in the presence and absence of autologous macrophages. The presence of macrophages in the culture increased the frequency of nonapoptotic GFP-positive productively infected CD4(+) T lymphocytes. The appearance of nonapoptotic productively infected CD4(+) T lymphocytes in the culture required intercellular contacts between macrophages and PBLs and the expression of the HIV Nef protein. The presence of macrophages did not reduce apoptosis when CD4(+) T lymphocytes were infected with a GFP-tagged virus deleted for the nef gene. TNF-alpha (TNF) expressed on the surface of macrophages prevented apoptosis in nef-expressing, productively infected CD4(+) T lymphocytes. Similarly, following TNF stimulation, apoptosis was diminished in Jurkat T cells transfected with a nef-expressing plasmid. TNF stimulation of nef-expressing Jurkat T cells resulted in NF-kappaB hyperactivation, which has been shown to deliver anti-apoptotic signals. Our results indicate that intercellular contacts with macrophages increase the rate of productively infected nonapoptotic CD4(+) T lymphocytes. The survival of productively infected CD4(+) T lymphocytes requires Nef expression as well as activation by TNF expressed on the surface of macrophages and might participate in the formation and maintenance of viral reservoirs in HIV-infected persons.     

Infection of white rat peritoneal macrophages with Toxoplasma gondii, (Coccidia: Sarcocystidae) after Trypanosoma lewisi (Kinetoplastida: Trypanosomatidae) infection

Peritoneal macrophages from Wistar rats, inoculated and non-inoculated with 10(6) T. lewisi trypomastigotes, were cultured and infected with 10(6) T. gondii tachyzoites. Multiplication rates of this parasite were studied after 1, 24 and 48 h of infection but there were not significant differences between the number of parasites found inside of macrophages coming, either from T. lewisi infected or non infected rats. On the other hand, in vivo studies of Toxoplasma multiplication inside peritoneal macrophages, showed that there is an increase of parasite number in cells from T. lewisi infected rats, as compared with those macrophages from non infected rats. This effect was statistically significant and was more evident after four days of infection. Therefore, it has been demonstrated that in vivo, but not in vitro T. lewisi infections, causes an important decrease of the natural resistance to T. gondii of the white rats, which is manifested by the major invasion and multiplication of the parasite inside of peritoneal macrophages.     

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.     

Toxoplasma gondii partially inhibits nitric oxide production of activated murine macrophages

Activated macrophages produce nitric oxide (NO) and as such are able to control the multiplication of Toxoplasma gondii. Until now, no reports have described a possible modulation of NO production of macrophages after T. gondii infection. To investigate this possibility, murine blood monocyte-derived and peritoneal macrophages were activated in vitro with interferon-gamma and lipopolysaccharide and infected with T. gondii and Trypanosoma cruzi, and NO production was evaluated. NO was produced by monocyte-derived macrophages only if cultured in the presence of macrophage-colony-stimulating factor. Monocyte-derived or peritoneal macrophages infected with T. gondii presented a significant reduction in NO production. NO production inhibition was not detected after T. cruzi infection. Macrophages infected with higher T. gondii/macrophage ratios presented lower NO production. Furthermore, only viable T. gondii could cause partial inhibition of NO production. In macrophages activated 24 h before the interaction, partial inhibition was detected after 3 h of infection and continued for 48 h. In macrophages activated immediately after the interaction, partial inhibition was not detected at 12 h, but was observed at 24 h. T. gondii-infected macrophages present lower inducible nitric oxide synthase expression as assayed by immunofluorescence. T. gondii did not develop in monocyte-derived macrophages producing NO, but were not totally eliminated. These results demonstrate that T. gondii infection partially inhibits NO production by murine macrophages, suggesting that a deactivating macrophage mechanism may be used for better survival into phagocytic cells.     

Alveolar macrophages are indispensable for controlling influenza viruses in lungs of pigs

Alveolar macrophages constitutively reside in the respiratory tracts of pigs and humans. An in vivo role of alveolar macrophages in defending against influenza viruses in mice infected with a reassorted influenza virus, 1918 HA/NA:Tx/91, was reported, but there has been no report on an in vivo role of alveolar macrophages in a natural host such as a pig using currently circulating human influenza virus. Here we show that in vivo depletion of alveolar macrophages in pigs by dichloromethylene diphosphonate (MDPCL2) treatment results in 40% mortality when pigs are infected with currently circulating human H1N1 influenza viruses, while none of the infected control pigs died. All infected pigs depleted of alveolar macrophages suffered from more severe respiratory signs than infected control pigs. Induction of tumor necrosis factor alpha in the infected pigs depleted of alveolar macrophages was significantly lower than that in the lungs of infected control pigs, and the induction of interleukin-10, an immunosuppressive cytokine, significantly increased in the lungs of infected pigs depleted of alveolar macrophages compared to infected control pigs. When we measured antibody titers and CD8(+) T lymphocytes expressing gamma interferon (IFN-gamma), lower antibody titers and a lower percentage of CD8(+) T lymphocytes expressing IFN-gamma were detectable in MDPCL2-treated infected pigs than in phosphate-buffered saline- and liposome-treated and infected pigs. Taken together, our findings suggest that alveolar macrophages are essential for controlling H1N1 influenza viruses in pigs.     

Cross-presentation of Listeria monocytogenes-derived CD4 T cell epitopes

Listeriolysin O (LLO) mediates the evasion of Listeria monocytogenes from the phagolysosome into the cytoplasm of the host cell. The recognition of infected cells by CD4 T cells is thought to be limited by the evasion of bacteria from the phagolysosome and also by the direct LLO-mediated inhibition of CD4 T cell activation. To analyze the influence of these immunoevasive mechanisms on the antilisterial CD4 T cell response, the expansion of L. monocytogenes-specific CD4 and CD8 T cells was monitored in infected mice. It was found that expansion of L. monocytogenes-specific CD4 T cells occurred synchronously with CD8 T cell expansion. The analysis of Ag presentation by macrophages and dendritic cells isolated from spleens of infected mice revealed efficient presentation of L. monocytogenes-derived CD4 T cell epitopes that was not dependent on the actA-mediated intercellular spread of bacteria. The further in vitro Ag presentation analysis revealed that although L. monocytogenes-infected macrophages and dendritic cells were poor presenters of CD4 T cell epitopes, more efficient presentation occurred after cocultivation of noninfected dendritic cells or macrophages with infected cells. These data indicate that the suppressive effect of LLO on the antilisterial CD4 T cell response is maintained only in infected APC and support the hypothesis that cross-priming plays a role in the induction of the strong CD4 T cell response in Listeria-infected mice.     

Lipids, apoptosis, and cross-presentation: links in the chain of host defense against Mycobacterium tuberculosis

Eicosanoids regulate whether human and murine macrophages infected with Mycobacterium tuberculosis die by apoptosis or necrosis. The death modality is important since apoptosis is associated with diminished pathogen viability and should be viewed as a form of innate immunity. Apoptotic vesicles derived from infected macrophages are also an important source of bacterial antigens that can be acquired by dendritic cells to prime antigen-specific T cells. This review integrates in vitro and in vivo data on how apoptosis of infected macrophages is linked to development of T cell immunity against M. tuberculosis.     

GM-CSF-mediated T-cell activation by macrophages infected with recombinant BCG that secretes major membrane protein-II of Mycobacterium leprae

The potential of Mycobacterium bovis Bacillus Calmette–Guerin (BCG) needs to be augmented to efficiently activate CD4⁺ T cells through macrophages. Mycobacterium leprae -derived recombinant major membrane protein (MMP)-II induced GM-CSF production from macrophages. A recombinant BCG-SM that secretes MMP-II more efficiently produced GM-CSF and activated interferon (IFN)-γ-producing CD4⁺ T cells than did vector control BCG when infected with macrophages. The T-cell activation by BCG-SM was dependent on the GM-CSF production by macrophages. Interleukin (IL)-10 production by macrophages stimulated with M. leprae was inhibited in a GM-CSF-dependent manner when the precursor monocytes were infected with BCG-SM. BCG inducing GM-CSF production was effective in macrophage-mediated T-cell activation partially through IL-10 inhibition.     

Accumulation of MAC387+ macrophages in paracortical areas of lymph nodes in rhesus monkeys acutely infected with simian immunodeficiency virus

We investigated the histological features of lymph nodes, focusing on monocytes/macrophages, in rhesus monkeys (Macaca mulatta) acutely infected with simian immunodeficiency virus (SIV). In monkeys infected with a pathogenic SIV, SIVmac239, MAC387(+) newly blood-derived macrophages markedly increased in number at paracortical areas at 11 to 14 days postinoculation, concomitant with the peak of the primary SIV antigenemia. The MAC387(+) macrophages densely gathered around high endothelial venules and formed cell clusters with CD3(+) T lymphocytes, tingible body macrophages, and plasmacytoid monocytes. In the cell clusters, CD3(+) T lymphocytes which closely adhered to the MAC387(+) macrophages enlarged in size, suggesting a histological manifestation of T-lymphocyte activation by macrophages. By 54 days postinoculation, when SIV antigenemia became undetectable, the MAC387(+) macrophages decreased in number and the cell cluster disappeared from paracortical areas. In contrast, the monkeys infected with a nef-deleted mutant of SIVmac239 showed lower levels of SIV antigenemia and lower numbers of MAC387(+) macrophages in paracortical areas than those infected with SIVmac239. These results indicate that MAC387(+) macrophages accumulate in paracortical areas for the period of the intense primary SIV antigenemia and may play an important role in activating naive T lymphocytes.     

Effects of alpha- and beta-adrenergic agonists on Toxoplasma gondii infection in murine macrophages

We investigated the effects of alpha- and beta-adrenergic receptor agonists on the ability of Toxoplasma gondii to infect and proliferate in cultured murine macrophages. Macrophages pretreated in vitro with varying concentrations of alpha- and beta-adrenergic agonists and incubated with the RH strain of T. gondii did not result in a significant increase in the percentage of infected macrophages compared with negative controls. When parasites were pretreated with L-phenylephrine, an alpha-agonist, and L-isoproterenol, a beta-agonist, before infection, there was no significant change in the percentage of infected macrophages. Clonidine, an alpha2-adrenergic agonist, led to a significant decrease in the number of infected macrophages at all concentrations tested. The effects of clonidine were blocked by yohimbine, a specific alpha2-adrenergic antagonist, but not by phentolamine, an alpha1-adrenergic antagonist. These results suggest that the antiparasitic effects exhibited by clonidine (alpha2-adrenergic agonist) are mediated through an alpha2-adrenoreceptor found on the surface of T. gondii.     

Antigen-specific (p30) mouse CD8+ T cells are cytotoxic against Toxoplasma gondii-infected peritoneal macrophages.

The importance of CD8+ T cells in immunity against Toxoplasma gondii is now well recognized. The mechanism by which these CD8+ T cells are able to confer this immunity is not yet understood. To examine the Ag specificity of this response, immune splenocytes from mice immunized with p30, a major surface parasite Ag, were evaluated for their ability to lyse peritoneal macrophages infected with three different strains of T. gondii. Macrophages infected with either the RH or P wild-type strain tachyzoites were lysed at varying E:T ratios by nylon wool nonadherent immune splenocytes whereas macrophages infected with a p30-deficient mutant (B mutant) of the P strain were not. The gene encoding p30 for the wild type and B mutant were amplified by the polymerase chain reaction. This revealed a nonsense mutation in the B mutant such that its primary translation product is predicted to be about two-thirds the size of the wild-type p30 molecule. mAb depletion studies indicate that the cytotoxic effect of the immune splenocytes is mediated by the CD8+ T cell population. Peritoneal macrophages infected with the three different strains (RH, P wild type, B mutant) from mice genetically restricted were not lysed by the immune CD8+ effector cell population. A cloned line (C3) of p30 Ag-specific CD8+ T cells exhibited significant cytotoxicity against syngeneic peritoneal macrophages infected with either the RH or P strain tachyzoites. There was no macrophage lysis observed by these CD8+ effector cells of either syngeneic macrophages infected with the B mutant or nonsyngeneic macrophages infected with the three different tachyzoite strains.     

SIV Infection of Lung Macrophages

HIV-1 depletes CD4+ T cells in the blood, lymphatic tissues, gut and lungs. Here we investigated the relationship between depletion and infection of CD4+ T cells in the lung parenchyma. The lungs of 38 Indian rhesus macaques in early to later stages of SIVmac251 infection were examined, and the numbers of CD4+ T cells and macrophages plus the frequency of SIV RNA+ cells were quantified. We showed that SIV infected macrophages in the lung parenchyma, but only in small numbers except in the setting of interstitial inflammation where large numbers of SIV RNA+ macrophages were detected. However, even in this setting, the number of macrophages was not decreased. By contrast, there were few infected CD4+ T cells in lung parenchyma, but CD4+ T cells were nonetheless depleted by unknown mechanisms. The CD4+ T cells in lung parenchyma were depleted even though they were not productively infected, whereas SIV can infect large numbers of macrophages in the setting of interstitial inflammation without depleting them. These observations point to the need for future investigations into mechanisms of CD4+ T cell depletion at this mucosal site, and into mechanisms by which macrophage populations are maintained despite high levels of infection. The large numbers of SIV RNA+ macrophages in lungs in the setting of interstitial inflammation indicates that lung macrophages can be an important source for SIV persistent infection.     

Exosomes derived from M. Bovis BCG infected macrophages activate antigen-specific CD4+ and CD8+ T cells in vitro and in vivo

Activation of both CD4(+) and CD8(+) T cells is required for an effective immune response to an M. tuberculosis infection. However, infected macrophages are poor antigen presenting cells and may be spatially separated from recruited T cells, thus limiting antigen presentation within a granuloma. Our previous studies showed that infected macrophages release from cells small membrane-bound vesicles called exosomes which contain mycobacterial lipid components and showed that these exosomes could stimulate a pro-inflammatory response in na?ve macrophages. In the present study we demonstrate that exosomes stimulate both CD4(+) and CD8(+) splenic T cells isolated from mycobacteria-sensitized mice. Although the exosomes contain MHC I and II as well as costimulatory molecules, maximum stimulation of T cells required prior incubation of exosomes with antigen presenting cells. Exosomes isolated from M. bovis and M. tuberculosis infected macrophages also stimulated activation and maturation of mouse bone marrow-derived dendritic cells. Interestingly, intranasal administration of mice with exosomes isolated from M. bovis BCG infected macrophages induce the generation of memory CD4(+) and CD8(+) T cells. The isolated T cells also produced IFN-gamma upon restimulation with BCG antigens. The release of exosomes from infected macrophages may overcome some of the defects in antigen presentation associated with mycobacterial infections and we suggest that exosomes may be a promising M. tuberculosis vaccine candidate.     

Modeling the role of macrophages in HIV persistence during antiretroviral therapy

HIV preferentially infects activated CD4+ T cells. Current antiretroviral therapy cannot eradicate the virus. Viral infection of other cells such as macrophages may contribute to viral persistence during antiretroviral therapy. In addition to cell-free virus infection, macrophages can also get infected when engulfing infected CD4+ T cells as innate immune sentinels. How macrophages affect the dynamics of HIV infection remains unclear. In this paper, we develop an HIV model that includes the infection of CD4+ T cells and macrophages via cell-free virus infection and cell-to-cell viral transmission. We derive the basic reproduction number and obtain the local and global stability of the steady states. Sensitivity and viral dynamics simulations show that even when the infection of CD4+ T cells is completely blocked by therapy, virus can still persist and the steady-state viral load is not sensitive to the change of treatment efficacy. Analysis of the relative contributions to viral replication shows that cell-free virus infection leads to the majority of macrophage infection. Viral transmission from infected CD4+ T cells to macrophages during engulfment accounts for a small fraction of the macrophage infection and has a negligible effect on the total viral production. These results suggest that macrophage infection can be a source contributing to HIV persistence during suppressive therapy. Improving drug efficacies in heterogeneous target cells is crucial for achieving HIV eradication in infected individuals.

     

Functional Activity of Monocytes and Macrophages in HTLV-1 Infected Subjects

The Human T lymphotropic virus type-1 (HTLV-1) infects predominantly T cells, inducing proliferation and lymphocyte activation. Additionally, HTLV-1 infected subjects are more susceptible to other infections caused by other intracellular agents. Monocytes/macrophages are important cells in the defense against intracellular pathogens. Our aims were to determine the frequency of monocytes subsets, expression of co-stimulatory molecules in these cells and to evaluate microbicidal ability and cytokine and chemokine production by macrophages from HTLV-1 infected subjects. Participants were 23 HTLV-1 carriers (HC), 22 HAM/TSP patients and 22 healthy subjects (HS) not infected with HTLV-1. The frequencies of monocyte subsets and expression of co-stimulatory molecules were determined by flow cytometry. Macrophages were infected with L. braziliensis or stimulated with LPS. Microbicidal activity of macrophages was determined by optic microscopy. Cytokines/chemokines from macrophage supernatants were measured by ELISA. HAM/TSP patients showed an increase frequency of intermediate monocytes, but expression of co-stimulatory molecules was similar between the groups. Macrophages from HTLV-1 infected individuals were infected with L. braziliensis at the same ratio than macrophages from HS, and all the groups had the same ability to kill Leishmania parasites. However, macrophages from HTLV-1 infected subjects produced more CXCL9 and CCL5, and less IL-10 than cells from HS. While there was no correlation between IFN-γ and cytokine/chemokine production by macrophages, there was a correlation between proviral load and TNF and CXCL10. These data showed a dissociation between the inflammatory response and microbicidal ability of macrophages from HTLV-1 infected subjects. While macrophages ability to kill an intracellular pathogen did not differ among HTLV-1 infected subjects, these cells secreted high amount of chemokines even in unstimulated cultures. Moreover the increasing inflammatory activity of macrophages was similar in HAM/TSP patients and HC and it was related to HTLV-1 proviral load rather than the high IFN-γ production observed in these subjects.     

The Pseudomonas aeruginosa Type III Secretion System Has an Exotoxin S/T/Y Independent Pathogenic Role during Acute Lung Infection

The type III secretion system (T3SS) is a complex nanomachine of many pathogenic Gram-negative bacteria. It forms a proteinaceous channel that is inserted into the host eukaryotic cell membrane for injection of bacterial proteins that manipulate host cell signaling. However, few studies have focused on the effector-independent functions of the T3SS. Using a murine model of acute lung infection with Pseudomonas aeruginosa, an important human opportunistic pathogen, we compared the pathogenicity of mutant bacteria that lack all of the known effector toxins ( ΔSTY), with mutant bacteria that also lack the major translocator protein PopB (ΔSTY/ΔPopB) and so cannot form a functional T3SS channel in the host cell membrane. Mortality was higher among mice challenged with ΔSTY compared to mice challenged with ΔSTY/ΔPopB mutant bacteria. In addition, mice infected with ΔSTY showed decreased bacterial clearance from the lungs compared to those infected with ΔSTY/ΔPopB. Infection was in both cases associated with substantial killing of lung infiltrating macrophages. However, macrophages from ΔSTY-infected mice died by pro-inflammatory necrosis characterized by membrane permeabilization and caspase-1 mediated IL-1β production, whereas macrophages from ΔSTY/ΔPopB infected mice died by apoptosis, which is characterized by annexin V positive staining of the cell membrane and caspase-3 activation. This was confirmed in macrophages infected in vitro. These results demonstrate a T3SS effector toxin independent role for the T3SS, in particular the T3SS translocator protein PopB, in the pathogenicity of P. aeruginosa during acute lung infection.     

Reduction in adhesiveness to extracellular matrix components, modulation of adhesion molecules and in vivo migration of murine macrophages infected with Toxoplasma gondii

Toxoplasma gondii is an obligate intracellular parasite, able to disseminate into deep tissues and cross biological barriers, reaching immunoprivileged sites such as the brain and retina. In order to investigate whether the parasite uses leukocyte trafficking to disseminate throughout the host, the adhesive potential to extracellular matrix components, the expression of adhesion molecules and the in vivo migration of murine macrophages infected with RH strain of T. gondii were investigated. Cellular adhesion to fibronectin, laminin and collagen IV decreased after 24 h of T. gondii infection. However, the decrease in adhesion of infected macrophages observed at early infection was reversed after 48 h. Moreover, decreased adhesion was dependent on active penetration, since heat-killed parasites were unable to reproduce it. Expression of integrins alphaL, alpha4 and alpha5 chains was downmodulated early postinfection, but a progressive regain of expression was observed after 12 h of infection. Expression of beta2, alphav and alpha4 integrins by peritoneal macrophages at late infection was also gradually reestablished. The assessment of in vivo migration of infected macrophages labeled with the fluorescent dye 5-chloromethylfluorescein diacetate showed a 48-h delay in migration to cervical lymph nodes when compared to LPS pre-stimulated macrophages. Furthermore, cells that migrate to distal lymph nodes were loaded with live parasites. Taken together, these results provide insights about T. gondii escape from the host immune response, placing the macrophage as a "Trojan horse", contributing to parasite dissemination and access to immunoprivileged sites.     

Leishmania-induced inhibition of macrophage antigen presentation analyzed at the single-cell level

A number of studies have previously examined the capacity of intracellular Leishmania parasites to modulate the capacity of macrophages to process and present Ags to MHC class II-restricted CD4(+) T cells. However, the bulk culture approaches used for assessing T cell activation make interpretation of some of these studies difficult. To gain a more precise understanding of the interaction between Leishmania-infected macrophages and effector T cells, we have analyzed various parameters of T cell activation in individual macrophage-T cell conjugates. Leishmania-infected macrophages efficiently stimulate Ag-independent as well as Ag-dependent, TCR-mediated capping of cortical F-actin in DO.11 T cells. However, infected macrophages are less efficient at promoting the sustained TCR signaling necessary for reorientation of the T cell microtubule organizing center and for IFN-gamma production. A reduced ability to activate these T cell responses was not due to altered levels of surface-expressed MHC class II-peptide complexes. This study represents the first direct single-cell analysis of the impact of intracellular infection on the interaction of macrophages with T cells and serves to emphasize the subtle influence Leishmania has on APC function.     

Francisella tularensis-infected macrophages release prostaglandin E2 that blocks T cell proliferation and promotes a Th2-like response

Francisella tularensis is a highly infectious bacterial pathogen, and is likely to have evolved strategies to evade and subvert the host immune response. In this study, we show that F. tularensis infection of macrophages alters T cell responses in vitro, by blocking T cell proliferation and promoting a Th2-like response. We demonstrate that a soluble mediator is responsible for this effect and identify it as PGE(2). Supernatants from F. tularensis-infected macrophages inhibited IL-2 secretion from both MHC class I and MHC class II-restricted T cell hybridomas, as well as enhanced a Th2-like response by inducing increased production of IL-5. Furthermore, the soluble mediator blocked proliferation of naive MHC class I-restricted T cells when stimulated with cognate tetramer. Indomethacin treatment partially restored T cell proliferation and lowered IL-5 production to wild-type levels. Macrophages produced PGE(2) when infected with F. tularensis, and treatment of infected macrophages with indomethacin, a cyclooxygenase-1/cyclooxygenase-2 inhibitor, blocked PGE(2) production. To further demonstrate that PGE(2) was responsible for skewing of T cell responses, we infected macrophages from membrane PGE synthase 1 knockout mice (mPGES1(-/-)) that cannot produce PGE(2). Supernatants from F. tularensis-infected membrane PGE synthase 1(-/-) macrophages did not inhibit T cell proliferation. Furthermore, treatment of T cells with PGE(2) recreated the effects seen with infected supernatant. From these data, we conclude that F. tularensis can alter host T cell responses by causing macrophages to produce PGE(2). This study defines a previously unknown mechanism used by F. tularensis to modulate adaptive immunity.     

Change in the isoenzyme composition of acid phosphatase in murine peritoneal macrophages exposed to or infected with Trypanosoma cruzi

The effect of infection with Trypanosoma cruzi on the activity and isoenzyme composition of acid phosphatase within individual murine peritoneal macrophages maintained in vitro was studied. Concentrations of acid phosphatase activity and number of intracellular parasites were quantitated by using a computer-assisted cytospectrophotometry system. Changes in the isoenzyme composition of macrophages during infection with T. cruzi were detected by comparing the patterns of acid phosphatase levels between macrophages treated in the absence and presence of an enzyme inhibitor. It was observed that the concentration levels of acid phosphatase activity in macrophages did not change significantly by infection with T. cruzi. Also, the concentration levels of acid phosphatase activity did not change in macrophages uninfected but exposed to T. cruzi. On the other hand, the isoenzyme composition of acid phosphatase did change in macrophages exposed to or infected with T. cruzi. These results demonstrate that Trypanosoma cruzi affects the acid phosphatase composition of macrophages.