Role of Lsh in regulating macrophage priming/activation

Cytokines: Key Determinants of Resistance or Disease Progression in Visceral Leishmaniasis: Opportunities for Novel Diagnostics and Immunotherapy

Leishmaniasis is a parasitic disease of humans, highly prevalent in parts of the tropics, subtropics, and southern Europe. The disease mainly occurs in three different clinical forms namely cutaneous, mucocutaneous, and visceral leishmaniasis (VL). The VL affects several internal organs and is the deadliest form of the disease. Epidemiology and clinical manifestations of VL are variable based on the vector, parasite (e.g., species, strains, and antigen diversity), host (e.g., genetic background, nutrition, diversity in antigen presentation and immunity) and the environment (e.g., temperature, humidity, and hygiene). Chemotherapy of VL is limited to a few drugs which is expensive and associated with profound toxicity, and could become ineffective due to the parasites developing resistance. Till date, there are no licensed vaccines for humans against leishmaniasis. Recently, immunotherapy has become an attractive strategy as it is cost-effective, causes limited side-effects and do not suffer from the downside of pathogens developing resistance. Among various immunotherapeutic approaches, cytokines (produced by helper T-lymphocytes) based immunotherapy has received great attention especially for drug refractive cases of human VL. Therefore, a comprehensive knowledge on the molecular interactions of immune cells or components and on cytokines interplay in the host defense or pathogenesis is important to determine appropriate immunotherapies for leishmaniasis. Here, we summarized the current understanding of a wide-spectrum of cytokines and their interaction with immune cells that determine the clinical outcome of leishmaniasis. We have also highlighted opportunities for the development of novel diagnostics and intervention therapies for VL.

F₁ cross-breed between susceptible BALB/c and resistant Swiss mice infected with Leishmania major exhibit an intermediate phenotype for lesion sizes and type 1 cytokines but show low level of total IgG antibodies

Our current understanding of the host immune response during leishmaniases largely derives from studies performed in mice due to the intrusive techniques required to study infected human patients. Swiss mice are highly resistant to Leishmania infections in concordance with observed response in humans, while BALB/c mice indicate a high-susceptibility phenotype. Developing a cross-breed between BALB/c and Swiss mice may have important consequences on disease development, immune responses and parasite killing, as yet, response of the cross-breed to Leishmania infection is superficial. The aim of the present study was to determine disease course and immune responses in F₁ cross-breed between BALB/c and Swiss albino mice infected with L. major. Three mice groups were infected intradermally with stationary-phase L. major parasites with parental strains (BALB/c and Swiss albino) as controls. Lesion development was monitored weekly for 8 weeks and monocyte chemotactic protein (MCP-1), macrophage inflammatory protein (MIP-1α), interferon-gamma (IFN-γ) and IgG antibody quantified by enzyme-linked immunosorbent assay. The data were analysed using one-way analysis of variance and Tukey-Kramer test. Results indicated F₁ mice having intermediate lesion sizes, type 1 cytokine levels and footpad parasite loads as compared to the parental strains. However, the F₁ mice had low levels of IgG antibodies and parasite burden in the spleen. (P < 0.05). This study concludes that the F₁ cross-breed between resistant and susceptible mice may be used as a requisite model to study the role of genetics in leishmaniases and perhaps other intracellular parasites.

Immunobiology of visceral leishmaniasis

Visceral leishmaniasis (VL), commonly known as kala-azar, is caused by Leishmania donovani and Leishmania infantum (Leishmania chagasi in the Americas). These Leishmania species infect macrophages throughout the viscera, and parasites are typically found in the spleen, liver, and bone marrow. Patients with active disease typically exhibit marked immunosuppression, lack reactivity to the Leishmania skin test (LST), a delayed type hypersensitivity test, and their peripheral blood mononuclear cells (PBMC) fail to respond when stimulated with leishmanial antigens in vitro. However, most people infected with visceralizing species of Leishmania never develop disease. Understanding immune failure and the underlying immune mechanism that lead to disease as well as control of infection are key questions for research in this field. In this review, we discuss immunological events described in human and experimental VL and how these can affect the outcome of infection.

Balancing immunity and pathology in visceral leishmaniasis

Experimental visceral leishmaniasis (VL) caused by infection with Leishmania donovani results in the development of organ-specific immunity in the two main target tissues of infection, the spleen and the liver. The liver is the site of an acute resolving infection associated with the development of inflammatory granulomas around infected Kupffer cells, and resistance to reinfection. Paradoxically, the spleen is an initial site for the generation of cell-mediated immune responses, but ultimately becomes a site of parasite persistence with associated immunopathological changes. These include splenomegaly and a breakdown in tissue architecture that is postulated to contribute to the immunocompromized status of the host. The progressive development of splenic pathology is largely associated with high levels of TNF and interleukin (IL)-10. Follicular dendritic cell (DC) networks are lost, whereas TNF mediates the destruction of marginal zone macrophages and gp38(+) stromal cells, and IL-10 promotes impaired DC migration into T-cell areas with consequent ineffective T-cell priming. Splenic stromal cell function is also altered, promoting the selective development of IL-10-producing DC with immunoregulatory properties. Ultimately, a fine immunological balance determines responses that effectively promote parasite clearance in the liver and those that promote pathology in the spleen, and future investigation aims to separate these responses to offer further means of parasite control in chronically infected VL patients.

A role for tumor necrosis factor-alpha in remodeling the splenic marginal zone during Leishmania donovani infection

The development of secondary lymphoid organs is a highly regulated process, mediated by tumor necrosis factor (TNF) family cytokines. In contrast, the mechanisms controlling changes in lymphoid architecture that occur during infectious disease are poorly understood. Here we demonstrate that during infection with Leishmania donovani, the marginal zone of mice undergoes extensive remodeling, similar in extent to developmental abnormalities in mice lacking some TNF family cytokines. This process is selective, comprising a dramatic and rapid loss of marginal zone macrophages (MZMs). As a functional consequence, lymphocyte traffic into the white pulp is impaired during chronic leishmaniasis. Significantly, MZMs were preserved in L. donovani-infected B6.TNF-alpha(-/-) mice or mice that received anti-TNF-alpha antibodies, whereas studies in CD8(+) T-cell-deficient mice and in mice lacking functional CD95L, excluded a direct role for either cytotoxic T lymphocyte activity or CD95-mediated apoptosis in this process. Loss of MZMs was independent of parasite burden, yet could be partially prevented by chemotherapy, which in turn reduced endogenous TNF-alpha levels. This is the first report of an infectious agent causing selective and long-lasting changes to the marginal zone via TNF-alpha-mediated mechanisms, and illustrates that those cytokines involved in establishing lymphoid architecture during development, may also play a role in infection-induced lymphoid tissue remodeling.

Fatal outcome of disseminated Mycobacterium avium infection in childhood. A case of primary incompetent monocyte/macrophage function?

Disseminated BCG infection rarely heals, and disseminated disease caused by the Mycobacterium avium complex usually has a poor prognosis with a short time to death. The case of a boy who died after 9 years of diagnosed disseminated M. avium complex infection is described. He showed no signs of previously known immunodeficiency except an incompetent primary monocyte/macrophage function. This case has been commented on in Acta Paediatrica Scandinavia (1982) as "the first infant to survive a generalized BCG infection".

Growth of Mycobacterium tuberculosis in BCG-resistant and -susceptible mice: establishment of latency and reactivation

Growth of mycobacterial species is controlled by a gene, Bcg (candidate Nramp). Bcg acts at the macrophage level and is thought to control some aspect of macrophage priming for activation. Infection of Mycobacterium bovis BCG-susceptible (Bcgs) mice with several different mycobacterial species results in the growth of the microorganisms, while the growth of the same organisms is controlled in BCG-resistant (Bcgr) mice. The capacity of Bcg to control the growth of M. tuberculosis has not been extensively explored. The purpose of this investigation, therefore, was to compare the growth of M. tuberculosis in Bcgr and Bcgs mice. We found that the growth of tubercule bacilli was different in the lungs and spleens of Bcgr and Bcgs mice when they were inoculated with fewer then 10(3) CFU of the mycobacterium. The differences in growth were more easily distinguished in the lungs then in the spleens. The growth of the microorganisms in both strains of mice peaked between 35 and 43 days, and a latent infection was established by 65 days after infection. Activation of the hypothalamic-pituitary-adrenal axis resulted in reactivation of the growth of M. tuberculosis in both Bcgr and Bcgs mice. Greater numbers of tubercule bacilli were isolated from lungs than from spleens following reactivation. The utility of this mouse model in the study of the establishment of latency and reactivation of M. tuberculosis is discussed.

Induction of interleukin 1 alpha in murine macrophages infected in vitro with different species and strains of Leishmania

It is now generally agreed that several cytokines released by immunocompetent cells such as macrophages play a crucial role in the outcome of infections caused by protozoa belonging to the genus Leishmania. In particular, tumor necrosis factor (TNF) induction during the course of cutaneous leishmaniasis has been related to resistance to L. major infection in mice. However, the role played by interleukin 1 (IL-1) in the host response to leishmaniasis has yet to be completely elucidated. The aim of this work was to study whether different species and strains of Leishmania could induce IL-1 alpha in murine macrophages in vitro. Resident peritoneal macrophages of BALB/c and C3H/HeN mice were infected with L. donovani, L. major, or different strains of L. infantum. It was found that L. donovani did not induce IL-1 alpha in macrophages from either mice strain. Infection with L. major or with three out of six strains of L. infantum induced consistent amounts of IL-1 alpha, but only in macrophages from genetically resistant C3H/HeN mice. No relationship was found between the rate of infection of macrophages and the amount of IL-1 alpha detected in the supernatants of infected macrophages. Data obtained confirm that the release of IL-1 alpha by murine macrophages infected in vitro with Leishmania is influenced by the genetic background of the cells as well as by the parasite species.

Familial disseminated atypical mycobacterial infection in childhood: a human mycobacterial susceptibility gene?

Inherited defects in specific components of the immune system have provided many clues to the immunological mechanisms underlying resistance to microbial infection. We report a familial immune defect predisposing to disseminated atypical mycobacterial infection in childhood. 6 children with disseminated atypical mycobacterial infection and no recognised form of immunodeficency were identified. Four, including two brothers, come from a village in Malta, and two are brothers of Greek Cypriot origin. They presented with fever, weight loss, lymphadenopathy, and hepatosplenomegaly. They had anaemia and an acute phase response. A range of different mycobacteria (Mycobacterium fortuitum, M chelonei, and four strains of M avium intracellulare complex) were isolated. Treatment with multiple antibiotics failed to eradicate the infection, although treatment with gamma interferon was associated with improvement. Three have died and the surviving children have chronic infection. Tumour necrosis factor-alpha production in response to endotoxin and gamma-interferon was found to be defective in affected patients and their parents. T-cell proliferative responses to mycobacterial and recall antigens were reduced in parents of affected children and gamma-interferon production was diminished in the affected patients and their parents. Clinical and immunological features suggest that these patients are phenotypically similar to Lsh/Ity/Bcg susceptible mice. Understanding of this defect may provide insights into the mechanisms responsible for susceptibility to mycobacteria.

Genetic regulation of leishmanial and mycobacterial infections: the Lsh/Ity/Bcg gene story continues

A common basis to genetic regulation of leishmanial and mycobacterial infections is provided by the action of the murine Lsh/Ity/Bcg gene in controlling the priming/activation of macrophages for antimicrobial activity. This relies on the TNF-alpha-dependent sustained expression of the inducible nitric oxide synthase (iNOS) gene responsible for the generation of large amounts of toxic nitric oxide (NO). The Lsh/Ity/Bcg gene has many pleiotropic effects, including differential expression of the early response gene KC following stimulation of macrophages with bacterial lipopolysaccharide (LPS) and mycobacterial lipoarabinomannan (LAM). The major signal transduction pathway involved in KC induction requires the generation of low levels of NO via constitutive nitric oxide synthase (cNOS) activity, leading to activation of guanylate cyclase and the cGMP-dependent kinase pathway. NO therefore appears to provide a common link between the early influence of Lsh in regulating the expression of genes which mediate many pleiotropic effects, and the later production of NO as the final effector mechanism for kill. The recently cloned candidate for Lsh/Ity/Bcg, designated Nramp for Natural resistance associated macrophage protein, encodes a polytopic integral membrane protein that has structural features common to prokaryotic and eukaryotic transporters and includes a conserved binding-protein-dependent transport motif which may be involved in interaction with peripheral ATP-binding subunits. The N-terminal sequence also carries a proline/serine rich putative SH3 binding domain, consistent with a role for tyrosine kinases in regulating Nramp function. (ABSTRACT TRUNCATED AT 250 WORDS)

Familial disseminated atypical mycobacterial disease

Mycobacterial disease remains a major public health problem and there appears to be a genetic component underlying susceptibility. This paper describes a group of related children who appear to have a genetic predisposition to disseminated atypical mycobacterial infection. Identification of the defect in this group could lead to better understanding of the genetics of susceptibility to mycobacterial infection.

Influence of macrophage resistance gene Lsh/Ity/Bcg (candidate Nramp) on Toxoplasma gondii infection in mice

Functional studies have shown that the murine macrophage resistance gene Lsh/Ity/Bcg (candidate Nramp) regulates macrophage priming/activation for antimicrobial activity via the tumour necrosis factor-alpha (TNF-alpha)-dependent production of reactive nitrogen intermediates. Since Toxoplasma gondii also parasitizes macrophages, is a stimulator of endogenous TNF-alpha release, and is sensitive to nitric oxide-mediated killing in activated macrophages, studies were carried out using chromosome 1 congenic mouse strains to determine whether Lsh influences T. gondii infection. Two interesting observations were made: (i) contrary to expectation, mice carrying the Lsh-resistant allele died earlier over the acute phase of infection than Lsh-susceptible mice; and (ii) Lsh-resistant mice which survived this acute phase of infection showed lower brain cyst numbers than the Lsh-susceptible mice. Whilst the latter occurred independently of route of inoculation (oral, intraperitoneal, or subcutaneous), the former was influenced both by the route of inoculation and the genetic background on which the Lsh-resistant allele had been isolated. Hence, following oral administration of 20 brain cysts of the RRA strain of T. gondii, mice carrying the Lsh-resistant allele on a B10 genetic background showed a significantly enhanced rate of mortality over the acute (first 8-12 days) phase of infection than B10 Lsh-susceptible mice. Although this acute phase of infection in B10 background mice was accompanied by an increase in serum TNF-alpha levels in both Lsh-resistant and -susceptible mouse strains, early mortality preceded the TNF-alpha peak, and administration of neutralizing rabbit anti-TNF-alpha did not significantly enhance survival. Hence, inflammatory mediators other than TNF-alpha appear to be responsible for the increased rate of acute mortality observed in resistant mice. Infection intraperitoneally led to delayed mortality in B10 mice, with the mean time to 50% mortality now being significantly longer in Lsh-resistant than in Lsh-susceptible mice. On a BALB genetic background, it was the i.p. route of infection which led to acute mortality and more rapid death in the Lsh-resistant strain. When a less virulent inoculum was used and mortality delayed, Lsh-susceptible mice died more rapidly, and i.p. administration of rabbit anti-TNF-alpha led to 100% mortality between days 8 and 10 of infection in both susceptible and resistant mouse strains, consistent with a crucial protective role for TNF-alpha during this phase of infection.(ABSTRACT TRUNCATED AT 400 WORDS)

Induction of early-response genes KC and JE by mycobacterial lipoarabinomannans: regulation of KC expression in murine macrophages by Lsh/Ity/Bcg (candidate Nramp)

The murine chromosome 1 gene Lsh/Ity/Bcg (candidate Nramp) regulates macrophage activation for antimicrobial activity against Salmonella typhimurium, Leishmania donovani, and Mycobacterium spp. To determine early events in the activation pathway, the ability of mycobacterial lipoarabinomannan (LAM) to induce early gene (KC and JE) expression in macrophages from susceptible (S) C57BL/10ScSn (Lshs) and congenic resistant (R) B10.L-Lshr mice was investigated. Stimulation with 1.8 microgram of arabinofuranosyl-terminated LAM (AraLAM) per ml resulted in similar kinetics for KC or JE expression in S and R macrophages. However, whereas JE/glyceraldehyde 3-phosphate dehydrogenase (GAPDH) mRNA ratios remained equivalent, R macrophages consistently showed enhanced KC/GAPDH ratios within 30 to 40 min of stimulation compared with S macrophages. Significant differences in KC/GAPDH ratios were observed throughout the peak period (0.5 to 6 h) of the KC response and with doses of AraLAM ranging from 0.01 to 2.5 micrograms/ml. Heavily mannosylated LAM from virulent Mycobacterium tuberculosis Erdman, in doses of up to 2.5 micrograms/ml, failed to stimulate KC or JE in S or R macrophages. Gamma interferon alone (25 U/ml) stimulated equivalent JE expression in S and R macrophages and synergized with AraLAM to enhance JE in both. In contrast, AraLAM-induced KC expression was inhibited in the presence of gamma interferon. Agonist/inhibitor studies were undertaken to determine the signal transduction pathways mediating KC expression. The protein kinase C (PKC) inhibitor Calphostin C (200 nM) inhibited AraLAM-induced KC by 34% +/- 4% in S macrophages and 43% +/- 5% in R macrophages; the cyclic AMP-dependent PKA inhibitor KT5720 (2 microM) inhibited AraLAM-induced KC by 33% +/- 4% (S) and 25% +/- 5% (R). A role for Ca2+ was indicated because ionophore alone stimulated KC expression and synergized with AraLAM to give a dramatically enhanced response. Induction of KC was also inhibited by (i) blocking constitutive nitric oxide (NO) production by preincubation of macrophages with NG-monomethyl-L-arginine (400 microM) (48% +/- 8% [S] and 40% +/- 11% [R]) and (ii) incubation of macrophages with the cyclic GMP-dependent kinase inhibitor KT5823 (4 microM) (65% +/- 4% [S] and 72% +/- 6% [R]). The manner in which these PKC-, PKA-, and Ca(2+)-dependent, NO-mediated cyclic GMP-dependent kinase signal transduction pathways may relate to function of the candidate Lsh/Ity/Bcg gene Nramp is discussed.

Regulation of mycobacterial growth by the hypothalamus-pituitary-adrenal axis: differential responses of Mycobacterium bovis BCG-resistant and -susceptible mice

The role of the hypothalamus-pituitary-adrenal (HPA) axis in regulating the growth of Mycobacterium avium in Mycobacterium bovis BCG-resistant and -susceptible congenic mice was evaluated. Restraint was used to activate the HPA axis, which resulted in an increase in the level of corticosterone in the plasma. Activation of the HPA axis increased the susceptibility of BALB/c.Bcgs mice to the growth of M. avium. In contrast, the growth of M. avium was not altered in BALB/c.Bcgr mice as a result of HPA activation. Adrenalectomy abolished the effect of HPA activation on mycobacterial growth, as did treatment of the mice with a glucocorticoid receptor antagonist, RU 486. Activation of the HPA axis also resulted in the increased susceptibility of splenic macrophages from Bcgs mice but not from Bcgr mice to M. avium growth in vitro. The production of tumor necrosis factor alpha and of reactive nitrogen intermediates by splenic macrophages from both strains of mice was suppressed as a result of HPA activation. The implications of these findings for resistance controlled by Bcg and for susceptibility to mycobacterial growth are discussed.

Leishmania donovani infection in scid mice: lack of tissue response and in vivo macrophage activation correlates with failure to trigger natural killer cell-derived gamma interferon production in vitro

Infection of immunocompetent mice with Leishmania donovani is characterized by the development of a tissue granulomatous response, in vivo macrophage activation, and a predominantly Th1-type CD4+ T-cell response. To determine whether a recently described T-cell-independent pathway of gamma interferon (IFN-gamma) production involving the collaboration of macrophages and natural killer (NK) cells contributed to this pattern of events, we have investigated the responses of scid mice to L. donovani infection. The multiplication of parasites in the livers of scid mice progressed at a rate equivalent to that seen in BALB/c mice over the first 14 days of infection, but by day 28 scid mice had a fivefold-higher parasite burden. This infection was not, however, accompanied by any demonstrable histological response in the liver or by elevated major histocompatibility complex class II expression on splenic macrophages. In vitro, L. donovani was unable to trigger IFN-gamma production from scid spleen cell cultures under conditions which allowed efficient triggering by bacterial stimuli. Although L. donovani also failed to stimulate the release of tumor necrosis factor, an important macrophage-derived cofactor for IFN-gamma secretion by NK cells, exogenous recombinant tumor necrosis factor alpha could not restore the IFN-gamma response. Even with the potent synergistic effect of exogenous interleukin-2, L. donovani was unable to stimulate this pathway to the same extent as Listeria monocytogenes. Indeed, L. donovani inhibited the response to L. monocytogenes in a dose-dependent fashion. Experiments involving the transfer of supernatants and the use of neutralizing monoclonal antibodies have failed to find evidence that interleukin-10 is involved in this inhibition. These data suggest that NK cell-derived IFN-gamma is unlikely to participate in the early regulation of visceral leishmaniasis in the mouse.

Recombinant interleukin-1 alpha augments granuloma formation and cytokine production but not parasite clearance in mice infected with Leishmania donovani

In vivo administration of various doses of recombinant interleukin-1 alpha to B10.D2/n mice chronically infected with Leishmania donovani resulted in enhanced formation of granulomas and in vitro production of gamma interferon. By direct microscopical enumeration, reduction in gross parasite burden in the viscera was not observed, however. These data highlight an important discordance between granuloma formation per se and parasite elimination and suggest that interleukin-1 deficiency alone cannot account for the chronicity of this disease.

Leishmaniasis epidemiology: all down to the DNA

Application of quantitative methods to the study of leishmaniasis epidemiology has allowed Dye (1992) to pinpoint important biological parameters which, if they could be accurately measured in the field, would contribute most to our knowledge of the spread of disease and key targets for control. Three areas in which laboratory-based research could impact most on leishmaniasis epidemiology were highlighted by Dye (1992): (i) the development of accurate diagnostic tools which can distinguish between current and past infection; (ii) to determine the underlying molecular/genetic basis to virulence polymorphisms in the parasite and study these in the context of field epidemiological studies; and (iii) to provide the molecular tools to measure genetic variation in resistance to infection in humans and in reservoir hosts of disease. This paper describes current progress in attaining these goals, highlighting first the work on isolation and field application of genomic and kDNA probes for species-specific diagnosis, and the development of PCR-based assays which can be performed under field conditions. At a more preliminary stage, studies are described in which variability in the major molecular determinants of virulence (lipophosphoglycan, GP63, and members of the HSP70 family of stress proteins) identified through studies of laboratory models of infection, is being measured in primary field isolates of Leishmania peruviana. To complete the picture, current progress in identifying and cloning the genes which control host resistance to leishmanial infection is described, along with field studies of multicase families of human disease in which linkage analysis using marker genes from the chromosomal regions bearing these genes can be used to find evidence for their role in determining disease phenotypes in man. The projected view from these studies is that the future of leishmaniasis epidemiology will be all down to the DNA.

Role of inorganic nitrogen oxides and tumor necrosis factor alpha in killing Leishmania donovani amastigotes in gamma interferon-lipopolysaccharide-activated macrophages from Lshs and Lshr congenic mouse strains

The capacity of mature bone-marrow-derived macrophages and resident peritoneal macrophages from Lshr versus Lshs congenic mice to kill intracellular Leishmania donovani amastigotes when activated by recombinant gamma interferon-lipopolysaccharide (rIFN-gamma-LPS) was examined. IFN-gamma alone in doses up to 100 U/ml was unable to activate macrophages to kill L. donovani amastigotes in vitro; LPS was a necessary secondary stimulus. Similarly, LPS alone in doses up to 100 ng/ml produced no leishmanicidal activity. In bone marrow macrophages, a dose-dependent increase in leishmanicidal activity was observed as increasing rIFN-gamma-LPS dose combinations were introduced, with Lshr macrophages maintaining a significant but not dramatic advantage within any particular dose combination. For peritoneal macrophages, the reverse was true, with macrophages from Lshs mice being more efficient at killing for doses of LPS up to 10 ng/ml with doses of rIFN-gamma in the range of 11 to 33 U/ml. The degree of killing in both bone marrow and peritoneal macrophages correlated well with the levels of nitrites measured in the supernatants at 72 h, and a highly significant correlation was observed between 4-, 24-, or 72-h tumor necrosis factor alpha (TNF-alpha) release and nitrite production measured at 72 h. Inclusion of 200 microM NG-monomethyl-L-arginine, a competitive inhibitor of the L-arginine-dependent pathway for the synthesis of inorganic nitrogen oxides, inhibited the killing, as did the addition of neutralizing anti-TNF-alpha antibody. These results are consistent with previous data showing an important autocrine role for TNF-alpha in enhancing production of inorganic nitrogen oxides by primed or activated macrophages. In addition, our results suggest that production of TNF-alpha and nitrites after priming or activation signals may be under a different regulatory control in mature bone marrow macrophages than in the resident peritoneal macrophage population.

Genetic regulation of macrophage priming/activation: the Lsh gene story

This paper describes functional and genetic studies on the macrophage resistance gene Lsh/Ity/Bcg first described almost two decades ago. Working in vitro with resident peritoneal, liver (Kupffer cells) and bone marrow derived macrophages from congenic B10 (LshS) and B10.L-LshR mice it has been possible to demonstrate that the final effector mechanism for the gene in regulating antileishmanial activity involves production of reactive nitrogen rather than reactive oxygen intermediates. This in turn is dependent upon priming/activation of macrophages for enhanced TNF-alpha release which acts back on the macrophage in an autocrine manner to increase nitric oxide production. The precise point at which Lsh acts to control macrophage priming/activation has not been identified, but studies of early response gene expression show differences in KC mRNA levels at 2 h after LPS stimulation, and in c-fos mRNA as early as 20 min after stimulation with PMA plus ionophore, in peritoneal macrophages from congenic LshS and LshR mice. Data available suggest that both negative and positive signals may be involved in macrophage priming/activation, with LshS macrophages down-regulating their capacity for continued response to the autocrine loop. Work in progress will examine the role of TPA and cAMP response element-binding proteins in regulating gene expression in Lsh congenic mice. A major new initiative has also commenced to clone the Lsh gene by reverse genetics using yeast artificial chromosomes to walk towards Lsh from the closet proximal and distal markers on mouse chromosome 1.(ABSTRACT TRUNCATED AT 250 WORDS)

Stimulation of antimycobacterial activity in mouse peritoneal macrophages by priming with trehalose dimycolate (TDM)

We examined the potential of two bacterial immunomodulators, trehalose dimycolate (TDM) and lipopolysaccharide (LPS), to stimulate the capacity of mouse peritoneal macrophages to control the growth of the intracellular bacterium, Mycobacterium tuberculosis BCG. Macrophages were obtained from mice innately susceptible (Bcgs) or resistant (Bcgr) to BCG infection. In all mouse strains tested (Bcgr and Bcgs), with the exception of BALB/c (Bcgs), TDM was sufficient to elicit macrophages with strong antimycobacterial activity in vitro. In BALB/c mice, the induction of anti-BCG activity required two signals, TDM and LPS, given in sequence. Our data suggest that additional gene(s), besides the Bcg locus, control macrophage resistance to BCG.

The involvement of TNF, IL-1 and IL-6 in the immune response to protozoan parasites

One early reaction of the host to infection with protozoan parasites is the secretion of an array of potent cytokines including tumor necrosis factor (TNF), interleukin (IL-1) and IL-6. The combined action of these cytokines causes fever, leukocytosis and the production of acute phase proteins such as C-reactive protein (CRP). These early responses contribute significantly to the outcome of infection by influencing the course of infection directly and by regulating the specific immune response to the parasite.