Rui Appelberg | Universidade do Porto (original) (raw)

Papers by Rui Appelberg

Journal of immunology (Baltimore, Md. : 1950), 2010

The ability of the thymus to generate a population of T cells that is, for the most part, self-re... more The ability of the thymus to generate a population of T cells that is, for the most part, self-restricted and self-tolerant depends to a great extent on the Ags encountered during differentiation. We recently showed that mycobacteria disseminate to the thymus, which raised the questions of how mycobacteria within the thymus influence T cell differentiation and whether such an effect impacts host-pathogen interactions. Athymic nude mice were reconstituted with thymic grafts from Mycobacterium avium-infected or control noninfected donors. T cells generated from thymi of infected donors seemed generally normal, because they retained the ability to reconstitute the periphery and to respond to unspecific stimuli in vitro as well as to antigenic stimulation with third-party Ags, such as OVA, upon in vivo immunization. However, these cells were unable to mount a protective immune response against a challenge with M. avium. The observation that thymic infection interferes with T cell differ...

Trends in Microbiology, 2007

Research in Immunology, 1996

The dissection of the mechanisms of immunity to M. &urn in mice

Medical Microbiology and Immunology, 2015

Mycobacterium avium subsp. paratuberculosis (MAP) has long been implicated as a triggering agent ... more Mycobacterium avium subsp. paratuberculosis (MAP) has long been implicated as a triggering agent in Crohn's disease (CD). In this study, we investigated the growth/persistence of both M. avium subsp. hominissuis (MAH) and MAP, in macrophages from healthy controls (HC), CD and ulcerative colitis patients. For viability assessment, both CFU counts and a pre16SrRNA RNA/DNA ratio assay (for MAP) were used. Phagolysosome fusion was evaluated by immunofluorescence, through analysis of LAMP-1 colocalization with MAP. IBD macrophages were more permissive to MAP survival than HC macrophages (a finding not evident with MAH), but did not support MAP active growth. The lower MAP CFU counts in macrophage cultures associated with Infliximab treatment were not due to increased killing, but possibly to elevation in the proportion of intracellular dormant non-culturable MAP forms, as MAP showed higher viability in those macrophages. Increased MAP viability was not related to lack of phagolysosome maturation. The predominant induction of MAP dormant forms by Infliximab treatment may explain the lack of MAP reactivation during anti-TNF therapy of CD but does not exclude the possibility of MAP recrudescence after termination of therapy.

International Journal of Experimental Pathology, 2006

Journal of immunology (Baltimore, Md. : 1950), 2012

Vaccine, 2015

Mycobacterium bovis Bacille Calmette-Guerin (BCG) is the only vaccine in use to prevent Mycobacte... more Mycobacterium bovis Bacille Calmette-Guerin (BCG) is the only vaccine in use to prevent Mycobacterium tuberculosis (Mtb) infection. Here we analyzed the protective efficacy of BCG against Mtb challenges 21 or 120 days after vaccination. Only after 120 days post-vaccination were mice able to efficiently induce early Mtb growth arrest and maintain long-lasting control of Mtb. This protection correlated with the accumulation of CD4 + T cells expressing IL-17 + TNF + IL-2 + . In contrast, mice challenged with Mtb 21 days after BCG vaccination exhibited only a mild and transient protection, associated with the accumulation of CD4 + T cells that were mostly IFN-␥ + TNF + and to a lesser extent IFN-␥ + TNF + IL-2 + . These data suggest that the memory response generated by BCG vaccination is functionally distinct depending upon the temporal proximity to BCG vaccination. Understanding how these responses are generated and maintained is critical for the development of novel vaccination strategies against tuberculosis.

Frontiers in Cellular and Infection Microbiology, 2013

† These authors have contributed equally to this work.

PLoS Neglected Tropical Diseases, 2013

Iron plays a central role in host-parasite interactions, since both intervenients need iron for s... more Iron plays a central role in host-parasite interactions, since both intervenients need iron for survival and growth, but are sensitive to iron-mediated toxicity. The host's iron overload is often associated with susceptibility to infection. However, it has been previously reported that iron overload prevented the growth of Leishmania major, an agent of cutaneous leishmaniasis, in BALB/c mice. In order to further clarify the impact of iron modulation on the growth of Leishmania in vivo, we studied the effects of iron supplementation or deprivation on the growth of L. infantum, the causative agent of Mediterranean visceral leishmaniasis, in the mouse model. We found that dietary iron deficiency did not affect the protozoan growth, whereas iron overload decreased its replication in the liver and spleen of a susceptible mouse strain. The fact that the iron-induced inhibitory effect could not be seen in mice deficient in NADPH dependent oxidase or nitric oxide synthase 2 suggests that iron eliminates L. infantum in vivo through the interaction with reactive oxygen and nitrogen species. Iron overload did not significantly alter the mouse adaptive immune response against L. infantum. Furthermore, the inhibitory action of iron towards L. infantum was also observed, in a dose dependent manner, in axenic cultures of promastigotes and amastigotes. Importantly, high iron concentrations were needed to achieve such effects. In conclusion, externally added iron synergizes with the host's oxidative mechanisms of defense in eliminating L. infantum from mouse tissues. Additionally, the direct toxicity of iron against Leishmania suggests a potential use of this metal as a therapeutic tool or the further exploration of iron anti-parasitic mechanisms for the design of new drugs.

Trends in Microbiology, 2002

In several murine models of mycobacterial infection, the absence of IFN-γ γ and/or NO results in ... more In several murine models of mycobacterial infection, the absence of IFN-γ γ and/or NO results in dysregulated granuloma formation and increased lymphocytic responses, which, in the case of M. avium infection, even leads to reduced bacterial growth.

Immunology, 2001

Interleukin-12 (IL-12) is a crucial cytokine for the generation of a protective immune response a... more Interleukin-12 (IL-12) is a crucial cytokine for the generation of a protective immune response against Mycobacterium avium infection. In contrast to infected control mice, IL-12-de®cient mice were unable to control bacterial proliferation and their spleen T cells were almost unresponsive in vitro to speci®c antigens of M. avium. Susceptibility of mice de®cient in IL-12 was similar to that of interferon-c (IFN-c)-de®cient mice. These data indicate a crucial role of IL-12 in the development of a T-cell population able to produce IFN-c and to mediate protection against M. avium infection. Treatment of M. avium-infected mice with IL-12 induced CD4 + T cells with enhanced capacity to produce IFN-c as well as to confer increased protection against M. avium.

PLoS Pathogens, 2011

Two-cysteine peroxiredoxins are ubiquitous peroxidases that play various functions in cells. In L... more Two-cysteine peroxiredoxins are ubiquitous peroxidases that play various functions in cells. In Leishmania and related trypanosomatids, which lack catalase and selenium-glutathione peroxidases, the discovery of this family of enzymes provided the molecular basis for peroxide removal in these organisms. In this report the functional relevance of one of such enzymes, the mitochondrial 2-Cys peroxiredoxin (mTXNPx), was investigated along the Leishmania infantum life cycle. mTXNPx null mutants (mtxnpx 2 ) produced by a gene replacement strategy, while indistinguishable from wild type promastigotes, were found unable to thrive in a murine model of infection. Unexpectedly, however, the avirulent phenotype of mtxnpx 2 was not due to lack of the peroxidase activity of mTXNPx as these behaved like controls when exposed to oxidants added exogenously or generated by macrophages during phagocytosis ex vivo. In line with this, mtxnpx 2 were also avirulent when inoculated into murine hosts unable to mount an effective oxidative phagocyte response (B6.p47 phox2/2 and B6.RAG2 2/2 IFN-c 2/2 mice). Definitive conclusion that the peroxidase activity of mTXNPx is not required for parasite survival in mice was obtained by showing that a peroxidase-inactive version of this protein was competent in rescuing the non-infective phenotype of mtxnpx 2 . A novel function is thus proposed for mTXNPx, that of a molecular chaperone, which may explain the impaired infectivity of the null mutants. This premise is based on the observation that the enzyme is able to suppress the thermal aggregation of citrate synthase in vitro. Also, mtxnpx 2 were more sensitive than controls to a temperature shift from 25uC to 37uC, a phenotype reminiscent of organisms lacking specific chaperone genes. Collectively, the findings reported here change the paradigm which regards all trypanosomatid 2-Cys peroxiredoxins as peroxide-eliminating devices. Moreover, they demonstrate, for the first time, that these 2-Cys peroxiredoxins can be determinant for pathogenicity independently of their peroxidase activity.

PLoS ONE, 2013

Important for both host and pathogen survivals, iron is a key factor in determining the outcome o... more Important for both host and pathogen survivals, iron is a key factor in determining the outcome of an infectious process. Iron with-holding, including sequestration inside tissue macrophages, is considered an important strategy to fight infection. However, for intra-macrophagic pathogens, such as Mycobacterium avium, host defence may depend on intracellular iron sequestration mechanisms. Ferritin, the major intracellular iron storage protein, plays a critical role in this process. In the current study, we studied ferritin expression in mouse bone marrow-derived macrophages upon infection with M. avium. We found that H-ferritin is selectively increased in infected macrophages, through an up-regulation of gene transcription. This increase was mediated by the engagement of Toll like receptor-2, and was independent of TNF-alpha or nitric oxide production. The formation of H-rich ferritin proteins and the consequent iron sequestration may be an important part of the panoply of antimicrobial mechanisms of macrophages.

Infection and Immunity, 2000

Evidence showing that neutrophils play a protective role in the host response to infection by dif... more Evidence showing that neutrophils play a protective role in the host response to infection by different intracellular parasites has been published in the past few years. We assessed this issue with regard to the infection of mice with Mycobacterium tuberculosis. We found a chronic recruitment of neutrophils to the infection foci, namely, to the peritoneal cavity after intraperitoneal infection and to the spleen and liver after intravenous inoculation of the mycobacteria. However, bacilli were never found associated with the recruited neutrophils but rather were found inside macrophages. The intravenous administration of the antineutrophil monoclonal antibody RB6-8C5 during the first week of infection led to selective and severe neutropenia associated with an enhancement of bacillary growth in the target organs of the mice infected by the intravenous route. The neutropenia-associated exacerbation of infection was most important in the liver, where a bacterial load 10-fold higher than that in nonneutropenic mice was found; the exacerbation in the liver occurred both during and after the neutropenic period. Early in infection by M. tuberculosis, neutropenic mice expressed lower levels of mRNAs for gamma interferon and inducible nitric oxide synthase in the liver compared to nondepleted mice. These results point to a protective role of neutrophils in the host defense mechanisms against M. tuberculosis, which occurs early in the infection and is not associated with the phagocytic activity of neutrophils but may be of an immunomodulatory nature.

Microbial Pathogenesis, 1989

Ft. Appelberg. Neutrophil-macrophage cooperation in the host defence against mycobacterial infect... more Ft. Appelberg. Neutrophil-macrophage cooperation in the host defence against mycobacterial infections. Microbial Pathogenesis 1989; 6: 369-380.

Microbial Pathogenesis, 2007

The growth in C57Bl/6 mice of seven distinct Mycobacterium avium strains was not exacerbated by t... more The growth in C57Bl/6 mice of seven distinct Mycobacterium avium strains was not exacerbated by the disruption of the inducible (type 2) nitric oxide synthase regardless of the virulence of the strain. The susceptibility of this panel of M. avium strains to reactive nitrogen intermediates in a cell-free system, namely the exposure to acidified nitrite or to the NO donor NOC-18, showed that there is no correlation between strain virulence and the corresponding minimal bactericidal and minimal inhibitory concentrations for those compounds determined in vitro. r

Microbes and Infection, 2010

Iron accumulation has been suggested to contribute to an increase of the susceptibility to mycoba... more Iron accumulation has been suggested to contribute to an increase of the susceptibility to mycobacterial infections. In this study we tested the effect of an array of iron chelating ligands of the 3-hydroxy-4-pyridinone family, in the intramacrophagic growth of Mycobacterium avium. We found that bidentate chelators, namely N-alkyl-3-hydroxy-4-pyridinones and N-aryl-3-hydroxy-4-pyridinones, did not affect the growth of M. avium inside mouse macrophages. In the case of the hexadentate chelators, those synthesized using an alkylamine (CP262) or a benzene ring (CP252) to link the three bidentate units, did not have an inhibitory effect on intramacrophagic growth of M. avium while those synthesized from a tripodal structure to anchor the bidentate units were capable of inhibiting the intramacrophagic growth of M. avium. The molecule we designated CP777 had the strongest inhibitory activity. The growth-reducing activity of CP777 was abrogated when this molecule was saturated with iron. These results confirm that iron deprivation, by the use of iron chelating compounds, restricts M. avium growth and that new iron chelators offer an approach to controlling mycobacterial infections.

Microbes and Infection, 2007

Mycobacterial infections are among the major health threats worldwide. Ability to fight these inf... more Mycobacterial infections are among the major health threats worldwide. Ability to fight these infections depends on the host's immune response, particularly on macrophages and T lymphocytes produced by the thymus. Using the mouse as a model, and two different routes of infection (aerogenic or intravenous), we show that the thymus is consistently colonized by Mycobacterium tuberculosis, Mycobacterium avium or Mycobacterium bovis BCG. When compared to organs such as the liver and spleen, the bacterial load reaches a plateau at later time-points after infection. Moreover, in contrast with organs such as the spleen and the lung no granuloma were found in the thymus of mice infected with M. tuberculosis or M. avium. Since T cell differentiation depends, to a large extent, on the antigens encountered within the thymus, infection of this organ might alter the host's immune response to infection. Therefore, from now on, the thymus should be considered in studies addressing the immune response to mycobacterial infection.

Infection and Immunity, 2000

After infection with a low-virulence strain of Mycobacterium avium, C57BL/6 and C57BL/10 mice had... more After infection with a low-virulence strain of Mycobacterium avium, C57BL/6 and C57BL/10 mice had clear differences in the control of the infection in their livers and spleens. This difference in susceptibility was not associated with differences in the H-2 complex. It was dependent on the activity of CD4 ؉ T cells but unrelated to the ability of these cells to secrete gamma interferon or to the development of delayed-type hypersensitivity responses at 3 weeks of infection. It was associated with lower total numbers of CD4 ؉ cells present in infected spleens and was related to an earlier induction of protective T cells, as measured by adoptive-transfer assays. These data further strengthen the notion of gamma-interferon-independent mechanisms of protection against mycobacteria.

Journal of immunology (Baltimore, Md. : 1950), 2010

The ability of the thymus to generate a population of T cells that is, for the most part, self-re... more The ability of the thymus to generate a population of T cells that is, for the most part, self-restricted and self-tolerant depends to a great extent on the Ags encountered during differentiation. We recently showed that mycobacteria disseminate to the thymus, which raised the questions of how mycobacteria within the thymus influence T cell differentiation and whether such an effect impacts host-pathogen interactions. Athymic nude mice were reconstituted with thymic grafts from Mycobacterium avium-infected or control noninfected donors. T cells generated from thymi of infected donors seemed generally normal, because they retained the ability to reconstitute the periphery and to respond to unspecific stimuli in vitro as well as to antigenic stimulation with third-party Ags, such as OVA, upon in vivo immunization. However, these cells were unable to mount a protective immune response against a challenge with M. avium. The observation that thymic infection interferes with T cell differ...

Trends in Microbiology, 2007

Research in Immunology, 1996

The dissection of the mechanisms of immunity to M. &urn in mice

Medical Microbiology and Immunology, 2015

Mycobacterium avium subsp. paratuberculosis (MAP) has long been implicated as a triggering agent ... more Mycobacterium avium subsp. paratuberculosis (MAP) has long been implicated as a triggering agent in Crohn's disease (CD). In this study, we investigated the growth/persistence of both M. avium subsp. hominissuis (MAH) and MAP, in macrophages from healthy controls (HC), CD and ulcerative colitis patients. For viability assessment, both CFU counts and a pre16SrRNA RNA/DNA ratio assay (for MAP) were used. Phagolysosome fusion was evaluated by immunofluorescence, through analysis of LAMP-1 colocalization with MAP. IBD macrophages were more permissive to MAP survival than HC macrophages (a finding not evident with MAH), but did not support MAP active growth. The lower MAP CFU counts in macrophage cultures associated with Infliximab treatment were not due to increased killing, but possibly to elevation in the proportion of intracellular dormant non-culturable MAP forms, as MAP showed higher viability in those macrophages. Increased MAP viability was not related to lack of phagolysosome maturation. The predominant induction of MAP dormant forms by Infliximab treatment may explain the lack of MAP reactivation during anti-TNF therapy of CD but does not exclude the possibility of MAP recrudescence after termination of therapy.

International Journal of Experimental Pathology, 2006

Journal of immunology (Baltimore, Md. : 1950), 2012

Vaccine, 2015

Mycobacterium bovis Bacille Calmette-Guerin (BCG) is the only vaccine in use to prevent Mycobacte... more Mycobacterium bovis Bacille Calmette-Guerin (BCG) is the only vaccine in use to prevent Mycobacterium tuberculosis (Mtb) infection. Here we analyzed the protective efficacy of BCG against Mtb challenges 21 or 120 days after vaccination. Only after 120 days post-vaccination were mice able to efficiently induce early Mtb growth arrest and maintain long-lasting control of Mtb. This protection correlated with the accumulation of CD4 + T cells expressing IL-17 + TNF + IL-2 + . In contrast, mice challenged with Mtb 21 days after BCG vaccination exhibited only a mild and transient protection, associated with the accumulation of CD4 + T cells that were mostly IFN-␥ + TNF + and to a lesser extent IFN-␥ + TNF + IL-2 + . These data suggest that the memory response generated by BCG vaccination is functionally distinct depending upon the temporal proximity to BCG vaccination. Understanding how these responses are generated and maintained is critical for the development of novel vaccination strategies against tuberculosis.

Frontiers in Cellular and Infection Microbiology, 2013

† These authors have contributed equally to this work.

PLoS Neglected Tropical Diseases, 2013

Iron plays a central role in host-parasite interactions, since both intervenients need iron for s... more Iron plays a central role in host-parasite interactions, since both intervenients need iron for survival and growth, but are sensitive to iron-mediated toxicity. The host's iron overload is often associated with susceptibility to infection. However, it has been previously reported that iron overload prevented the growth of Leishmania major, an agent of cutaneous leishmaniasis, in BALB/c mice. In order to further clarify the impact of iron modulation on the growth of Leishmania in vivo, we studied the effects of iron supplementation or deprivation on the growth of L. infantum, the causative agent of Mediterranean visceral leishmaniasis, in the mouse model. We found that dietary iron deficiency did not affect the protozoan growth, whereas iron overload decreased its replication in the liver and spleen of a susceptible mouse strain. The fact that the iron-induced inhibitory effect could not be seen in mice deficient in NADPH dependent oxidase or nitric oxide synthase 2 suggests that iron eliminates L. infantum in vivo through the interaction with reactive oxygen and nitrogen species. Iron overload did not significantly alter the mouse adaptive immune response against L. infantum. Furthermore, the inhibitory action of iron towards L. infantum was also observed, in a dose dependent manner, in axenic cultures of promastigotes and amastigotes. Importantly, high iron concentrations were needed to achieve such effects. In conclusion, externally added iron synergizes with the host's oxidative mechanisms of defense in eliminating L. infantum from mouse tissues. Additionally, the direct toxicity of iron against Leishmania suggests a potential use of this metal as a therapeutic tool or the further exploration of iron anti-parasitic mechanisms for the design of new drugs.

Trends in Microbiology, 2002

In several murine models of mycobacterial infection, the absence of IFN-γ γ and/or NO results in ... more In several murine models of mycobacterial infection, the absence of IFN-γ γ and/or NO results in dysregulated granuloma formation and increased lymphocytic responses, which, in the case of M. avium infection, even leads to reduced bacterial growth.

Immunology, 2001

Interleukin-12 (IL-12) is a crucial cytokine for the generation of a protective immune response a... more Interleukin-12 (IL-12) is a crucial cytokine for the generation of a protective immune response against Mycobacterium avium infection. In contrast to infected control mice, IL-12-de®cient mice were unable to control bacterial proliferation and their spleen T cells were almost unresponsive in vitro to speci®c antigens of M. avium. Susceptibility of mice de®cient in IL-12 was similar to that of interferon-c (IFN-c)-de®cient mice. These data indicate a crucial role of IL-12 in the development of a T-cell population able to produce IFN-c and to mediate protection against M. avium infection. Treatment of M. avium-infected mice with IL-12 induced CD4 + T cells with enhanced capacity to produce IFN-c as well as to confer increased protection against M. avium.

PLoS Pathogens, 2011

Two-cysteine peroxiredoxins are ubiquitous peroxidases that play various functions in cells. In L... more Two-cysteine peroxiredoxins are ubiquitous peroxidases that play various functions in cells. In Leishmania and related trypanosomatids, which lack catalase and selenium-glutathione peroxidases, the discovery of this family of enzymes provided the molecular basis for peroxide removal in these organisms. In this report the functional relevance of one of such enzymes, the mitochondrial 2-Cys peroxiredoxin (mTXNPx), was investigated along the Leishmania infantum life cycle. mTXNPx null mutants (mtxnpx 2 ) produced by a gene replacement strategy, while indistinguishable from wild type promastigotes, were found unable to thrive in a murine model of infection. Unexpectedly, however, the avirulent phenotype of mtxnpx 2 was not due to lack of the peroxidase activity of mTXNPx as these behaved like controls when exposed to oxidants added exogenously or generated by macrophages during phagocytosis ex vivo. In line with this, mtxnpx 2 were also avirulent when inoculated into murine hosts unable to mount an effective oxidative phagocyte response (B6.p47 phox2/2 and B6.RAG2 2/2 IFN-c 2/2 mice). Definitive conclusion that the peroxidase activity of mTXNPx is not required for parasite survival in mice was obtained by showing that a peroxidase-inactive version of this protein was competent in rescuing the non-infective phenotype of mtxnpx 2 . A novel function is thus proposed for mTXNPx, that of a molecular chaperone, which may explain the impaired infectivity of the null mutants. This premise is based on the observation that the enzyme is able to suppress the thermal aggregation of citrate synthase in vitro. Also, mtxnpx 2 were more sensitive than controls to a temperature shift from 25uC to 37uC, a phenotype reminiscent of organisms lacking specific chaperone genes. Collectively, the findings reported here change the paradigm which regards all trypanosomatid 2-Cys peroxiredoxins as peroxide-eliminating devices. Moreover, they demonstrate, for the first time, that these 2-Cys peroxiredoxins can be determinant for pathogenicity independently of their peroxidase activity.

PLoS ONE, 2013

Important for both host and pathogen survivals, iron is a key factor in determining the outcome o... more Important for both host and pathogen survivals, iron is a key factor in determining the outcome of an infectious process. Iron with-holding, including sequestration inside tissue macrophages, is considered an important strategy to fight infection. However, for intra-macrophagic pathogens, such as Mycobacterium avium, host defence may depend on intracellular iron sequestration mechanisms. Ferritin, the major intracellular iron storage protein, plays a critical role in this process. In the current study, we studied ferritin expression in mouse bone marrow-derived macrophages upon infection with M. avium. We found that H-ferritin is selectively increased in infected macrophages, through an up-regulation of gene transcription. This increase was mediated by the engagement of Toll like receptor-2, and was independent of TNF-alpha or nitric oxide production. The formation of H-rich ferritin proteins and the consequent iron sequestration may be an important part of the panoply of antimicrobial mechanisms of macrophages.

Infection and Immunity, 2000

Evidence showing that neutrophils play a protective role in the host response to infection by dif... more Evidence showing that neutrophils play a protective role in the host response to infection by different intracellular parasites has been published in the past few years. We assessed this issue with regard to the infection of mice with Mycobacterium tuberculosis. We found a chronic recruitment of neutrophils to the infection foci, namely, to the peritoneal cavity after intraperitoneal infection and to the spleen and liver after intravenous inoculation of the mycobacteria. However, bacilli were never found associated with the recruited neutrophils but rather were found inside macrophages. The intravenous administration of the antineutrophil monoclonal antibody RB6-8C5 during the first week of infection led to selective and severe neutropenia associated with an enhancement of bacillary growth in the target organs of the mice infected by the intravenous route. The neutropenia-associated exacerbation of infection was most important in the liver, where a bacterial load 10-fold higher than that in nonneutropenic mice was found; the exacerbation in the liver occurred both during and after the neutropenic period. Early in infection by M. tuberculosis, neutropenic mice expressed lower levels of mRNAs for gamma interferon and inducible nitric oxide synthase in the liver compared to nondepleted mice. These results point to a protective role of neutrophils in the host defense mechanisms against M. tuberculosis, which occurs early in the infection and is not associated with the phagocytic activity of neutrophils but may be of an immunomodulatory nature.

Microbial Pathogenesis, 1989

Ft. Appelberg. Neutrophil-macrophage cooperation in the host defence against mycobacterial infect... more Ft. Appelberg. Neutrophil-macrophage cooperation in the host defence against mycobacterial infections. Microbial Pathogenesis 1989; 6: 369-380.

Microbial Pathogenesis, 2007

The growth in C57Bl/6 mice of seven distinct Mycobacterium avium strains was not exacerbated by t... more The growth in C57Bl/6 mice of seven distinct Mycobacterium avium strains was not exacerbated by the disruption of the inducible (type 2) nitric oxide synthase regardless of the virulence of the strain. The susceptibility of this panel of M. avium strains to reactive nitrogen intermediates in a cell-free system, namely the exposure to acidified nitrite or to the NO donor NOC-18, showed that there is no correlation between strain virulence and the corresponding minimal bactericidal and minimal inhibitory concentrations for those compounds determined in vitro. r

Microbes and Infection, 2010

Iron accumulation has been suggested to contribute to an increase of the susceptibility to mycoba... more Iron accumulation has been suggested to contribute to an increase of the susceptibility to mycobacterial infections. In this study we tested the effect of an array of iron chelating ligands of the 3-hydroxy-4-pyridinone family, in the intramacrophagic growth of Mycobacterium avium. We found that bidentate chelators, namely N-alkyl-3-hydroxy-4-pyridinones and N-aryl-3-hydroxy-4-pyridinones, did not affect the growth of M. avium inside mouse macrophages. In the case of the hexadentate chelators, those synthesized using an alkylamine (CP262) or a benzene ring (CP252) to link the three bidentate units, did not have an inhibitory effect on intramacrophagic growth of M. avium while those synthesized from a tripodal structure to anchor the bidentate units were capable of inhibiting the intramacrophagic growth of M. avium. The molecule we designated CP777 had the strongest inhibitory activity. The growth-reducing activity of CP777 was abrogated when this molecule was saturated with iron. These results confirm that iron deprivation, by the use of iron chelating compounds, restricts M. avium growth and that new iron chelators offer an approach to controlling mycobacterial infections.

Microbes and Infection, 2007

Mycobacterial infections are among the major health threats worldwide. Ability to fight these inf... more Mycobacterial infections are among the major health threats worldwide. Ability to fight these infections depends on the host's immune response, particularly on macrophages and T lymphocytes produced by the thymus. Using the mouse as a model, and two different routes of infection (aerogenic or intravenous), we show that the thymus is consistently colonized by Mycobacterium tuberculosis, Mycobacterium avium or Mycobacterium bovis BCG. When compared to organs such as the liver and spleen, the bacterial load reaches a plateau at later time-points after infection. Moreover, in contrast with organs such as the spleen and the lung no granuloma were found in the thymus of mice infected with M. tuberculosis or M. avium. Since T cell differentiation depends, to a large extent, on the antigens encountered within the thymus, infection of this organ might alter the host's immune response to infection. Therefore, from now on, the thymus should be considered in studies addressing the immune response to mycobacterial infection.

Infection and Immunity, 2000

After infection with a low-virulence strain of Mycobacterium avium, C57BL/6 and C57BL/10 mice had... more After infection with a low-virulence strain of Mycobacterium avium, C57BL/6 and C57BL/10 mice had clear differences in the control of the infection in their livers and spleens. This difference in susceptibility was not associated with differences in the H-2 complex. It was dependent on the activity of CD4 ؉ T cells but unrelated to the ability of these cells to secrete gamma interferon or to the development of delayed-type hypersensitivity responses at 3 weeks of infection. It was associated with lower total numbers of CD4 ؉ cells present in infected spleens and was related to an earlier induction of protective T cells, as measured by adoptive-transfer assays. These data further strengthen the notion of gamma-interferon-independent mechanisms of protection against mycobacteria.