Pathophysiology of experimental leishmaniasis: pattern of development of metastatic disease in the susceptible host

Polymerase chain reaction detection and inducible nitric-oxide synthase expression of Leishmania major in mice inoculated by two different routes

Introduction:

Leishmania major needs a sensitive and specific method for proper diagnosis. This study aims to study the course and histopathology of L. major in certain tissues of experimentally infected BALB/c mice after subcutaneous (sc) and intraperitoneal (ip) inoculation.

Materials and Methods:

After infecting BALB/c mice using sc and ip inoculation, the histopathology was studied. The kinetoplastic DNA polymerase chain reaction (PCR) for its molecular detection and detect the inducible nitric-oxide synthase (iNOS) pattern during the first 3 months of infection.

Result:

PCR could detect the presence of L. major in all spleens, lymph nodes, and skin ulcers by both inoculation routes while (33%) and (42%) of livers were positive after sc and ip routes, respectively. Chronic inflammatory cell infiltrates with capsulitis was found in the spleen, lymph nodes, and liver. Granulomas were found in the spleen and liver. There was a statistically significant difference in iNOS expression along the experiment in the spleen and lymph nodes by both routes and in the liver by ip only. Apart from the liver, iNOS could not be detected on the 2^nd week postinfection and was high after 1 month for both routes in all samples; a moderate decrease at 2 months and the highest decrease were detected after 3 months.

Conclusions:

L. major inoculation by both routes produce visceral disease in mice, and kinetoplastic DNA PCR can detect its presence from the 2^nd week up to the 3^rd month postinfection. The iNOS expression was high at 1 and 2 months and remained throughout the 3 months of the experiment; which plays an important role in the disease course and control.

Protective response to Leishmania major in BALB/c mice requires antigen processing in the absence of DM

Protection from the parasite Leishmania major is mediated by CD4 T cells. BALB/c mice are susceptible to L. major and show a nonprotective immunodominant CD4 T cell response to Leishmania homolog of activated receptor for c-kinase (LACK) 158-173. Host genes that underlie BALB/c susceptibility to L. major infections are poorly defined. DM, a nonclassical MHC class II molecule, due to its peptide editing properties has been shown to 1) edit the repertoire of peptides displayed by APC, and 2) focus the display of epitopes by APC to the immunodominant ones. We tested the hypothesis that deficiency of DM, by causing presentation of a different array of epitopes by infected APC than that presented by DM-sufficient APC, may change the course of L. major infection in the susceptible BALB/c mice. We show herein that unlike their susceptible wild-type counterparts, BALB/c mice deficient in DM are protected from infections with L. major. Furthermore, DM-deficient mice fail to display the immunodominant LACK 158-173 on infected APC. In its place, infected DM(-/-) hosts show elicitation of CD4 T cells specific for newer epitopes not presented by wild-type L. major-infected APC. Protection of BALB/c DM(-/-) mice is dependent on IFN-gamma. DM is thus a host susceptibility gene in BALB/c mice, and Ag processing in the absence of DM results in elicitation of a protective T cell response against L. major infections. This report suggests a novel mechanism to trigger host resistance against pathogens.

Polyarthritis associated with visceral leishmaniasis in a juvenile dog

Canine visceral leishmaniasis (CL) is a zoonosis and a chronic systemic disease characterized by a wide spectrum of clinical signs, including, in rare occasions, polyarthritis. This report describes a case of CL in an 8-month old male boxer dog with a history of lameness, fever and lymphadenopathy. A definitive diagnosis of CL was based on the observation of the Leishmania amastigotes seen concomitantly, and for the first time, in the lymph nodes aspiration smears (in macrophages), synovial fluid (in macrophages and neutrophils) and blood (in neutrophils). Despite this extensive dissemination of the parasite, the animal was successfully treated with a multi-step combination of meglumine antimoniate, aminosidine and allopurinol.

A Leishmania donovani gene that confers accelerated recovery from stationary phase growth arrest

We have isolated a gene, LdGF1, from the protozoan parasite Leishmania donovani. Overexpression of this gene confers a strong selective advantage in liquid culture after stationary phase growth arrest. We could show that recombinant L. donovani or Leishmania major, when overexpressing LdGF1, recover faster from a stationary phase growth arrest than control parasite strains. While no advantage of LdGF1 overexpression could be observed in log phase cultures or after a hydroxyurea-induced S-phase growth arrest, recovery from a cell cycle arrest due to serum deprivation was faster in LdGF1-overexpressing strains. This was found to be due to an accelerated release from a G(1) cell cycle arrest. By contrast, in a BALB/c mouse infection system, overexpression of LdGF1 in L. major resulted in reduced virulence. We conclude that increased levels of LdGF1 are beneficiary during recovery from G(1) cell cycle arrest, but pose a disadvantage inside a mammalian host. These results are discussed in the context of the observed loss of virulence during in vitro passage of Leishmania parasites.

Malnutrition alters the innate immune response and increases early visceralization following Leishmania donovani infection

Malnutrition is a risk factor for the development of visceral leishmaniasis. However, the immunological basis for this susceptibility is unknown. We have developed a mouse model to study the effect of malnutrition on innate immunity and early visceralization following Leishmania donovani infection. Three deficient diets were studied, including 6, 3, or 1% protein; these diets were also deficient in iron, zinc, and calories. The control diet contained 17% protein, was zinc and iron sufficient, and was provided ab libitum. Three days after infection with L. donovani promastigotes, the total extradermal (lymph nodes, liver, and spleen) and skin parasite burdens were equivalent in the malnourished (3% protein) and control mice, but in the malnourished group, a greater percentage (39.8 and 4.0%, respectively; P = 0.009) of the extradermal parasite burden was contained in the spleen and liver. The comparable levels of parasites in the footpads in the two diet groups and the higher lymph node parasite burdens in the well-nourished mice indicated that the higher visceral parasite burdens in the malnourished mice were not due to a deficit in local parasite killing but to a failure of lymph node barrier function. Lymph node cells from the malnourished, infected mice produced increased levels of prostaglandin E(2) (PGE(2)) and decreased levels of interleukin-10. Inducible nitric oxide synthase activity was significantly lower in the spleen and liver of the malnourished mice. Thus, malnutrition causes a failure of lymph node barrier function after L. donovani infection, which may be related to excessive production of PGE(2) and decreased levels of IL-10 and nitric oxide.

Chemiluminescence activity in whole blood phagocytes of dogs naturally infected with Leishmania infantum

Dogs are the domestic reservoir of Leishmania infantum, a vector-borne intracellular protozoan agent of human visceral leishmaniasis. The role of polymorphonuclear leukocytes (PMNs) in the immune defence against this parasite has been poorly studied. We have investigated the function of peripheral blood PMNs in naive beagle dogs that have been naturally exposed to phlebotomine vectors in an area highly endemic for canine leishmaniasis, and found infected by Leishmania at the end of the transmission season. Whole blood phagocyte oxidative metabolism was assessed by a rapid method that determines a luminol-amplified chemiluminescence (CL) emission. This was evaluated using either a soluble stimulant, phorbol mirystate acetate (PMA), or phagocytic stimuli, such as zymosan unopsonized (ZYM) or opsonized with autologous serum (OPZ). In blood samples taken 2 months after exposure to Leishmania transmission, data on CL emission revealed a significant decrease of reactive oxygen intermediates (ROI) production in the presence of both PMA and ZYM, compared with blood samples obtained from dogs before exposure. On the contrary, no variations in CL emission were detected in presence of OPZ. Our data indicate that immunological changes occur early in canine leishmaniasis and confirm that the role of PMNs and their products need to be clarified.

Immune adherence-mediated opsonophagocytosis: the mechanism of Leishmania infection

To mimic the sandfly pool feeding process and characterize the cellular and biochemical events that occur during the early stages of promastigote-host interaction, we developed an ex vivo model of human blood infection with Leishmania promastigotes. Within 30 s of blood contact, Leishmania promastigotes bind natural anti-Leishmania antibodies, which then activate the classical complement pathway and opsonization by the third component of complement. The opsonized promastigotes undergo an immune adherence reaction and bind quantitatively to erythrocyte CR1 receptors; opsonized Leishmania amastigotes also bind to erythrocytes. Progression of infection implies promastigote transfer from erythrocytes to acceptor blood leukocytes. After 10 min of ex vivo infection, 25% of all leukocytes contain intracellular parasites, indicating that blood cells are the early targets for the invading promastigotes. We propose that adaptation to the immune adherence mechanism aids Leishmania survival, promoting rapid promastigote phagocytosis by leukocytes. This facilitates host colonization and may represent the parasite's earliest survival strategy. In light of this mechanism, it is unlikely that infection-blocking vaccines can be developed.

Leishmania major Hsp100 is required chiefly in the mammalian stage of the parasite

In Leishmania major a 100-kDa heat shock protein, Hsp100, is abundant in the intracellular amastigote stage which persists in the mammalian host. A replacement of both clpB alleles which encode Hsp100 does not affect promastigote viability under standard culture conditions but impairs thermotolerance in vitro. In experimental infections of BALB/c inbred mice, the lack of Hsp100 in the gene replacement mutants results in a markedly delayed lesion development compared with that in infections with wild-type L. major. Overexpression of exogenous clpB gene copies can partly restore virulence to the gene replacement mutants. Genetic-selection experiments also reveal a strong pressure for Hsp100 expression in the mammalian stage. This requirement for Hsp100 was also observed in in vitro infection experiments with mouse peritoneal macrophages. These experiments indicated a role for Hsp100 during the development from the promastigote to the amastigote stage. Our results suggest an important role for this parasite heat shock protein during the initial stages of a mammalian infection.

Evaluation of polymorphonuclear cell and monocyte functions in Leishmania infantum-infected dogs

Leishmania infantum is the causative agent of canine leishmaniasis in the Mediterranean area. The aspects of the canine immune response which may explain the chronic severe disease in these animals have not been well investigated. Therefore, in this work we have evaluated the parasite killing ability by circulating polymorphonuclear (PMN) cells and monocytes in dogs with spontaneous leishmaniasis and in healthy dogs. Moreover, in order to analyse the mechanisms responsible for killing activity, we evaluated the oxidative burst of circulating PMN cells, in terms of O2- and H2O2 production. The killing ability of infected dog PMN cells and monocytes was significantly lower than in a group of healthy dogs and a group of infected dogs treated with meglumine antimoniate and without symptoms of leishmaniasis. Superoxide anion and hydrogen peroxide production by PMN cells was significantly lower in a group of Leishmania-infected dogs than in healthy dogs, suggesting that these mediators may be involved in the reduced killing activity of infected dogs.

Parasite escape mechanisms: the role of Leishmania lipophosphoglycan on the human phagocyte functions. A review

Protozoan parasites of the Leishmania genus are the causative agents of important diseases in humans and animals. During their life cycle in vertebrate hosts, protozoa are able to live and proliferate within phagolysosomes of host phagocytic cells. The capacity to live in this hostile environment is likely due to the cell surface glycoconjugate expression. In particular, lipophosphoglycan (LPG), a major surface glycoconjugate of Leishmania promastigotes, has been reported to play an active role in protecting parasites within phagolysosomes via the impairment of killing mechanisms. In this review, the authors emphasize some novel LPG-mediated escape mechanisms of promastigotes from human phagocyte responses, such as the impairment of oxidative burst and of chemotactic activity. In the light of these findings, the knowledge of biological actions of LPG may be useful in order to prepare a vaccine against human leishmaniasis, using LPG defective avirulent mutant strains.

Impairment of the human phagocyte oxidative responses caused by Leishmania lipophosphoglycan (LPG): in vitro studies

Lipophosphoglycan (LPG), a surface glycoconjugate of Leishmania promastigotes, has been reported as playing an active role in protecting the parasite within phagolysosomes, by an impairment of monocyte oxidative responses. In this study the effect of LPG on the oxidative burst of human peripheral monocytes, eosinophils and neutrophils was evaluated. Our results demonstrated that either superoxide anion (O2-) or hydrogen peroxide (H2O2) release by LPG-pretreated cells was diminished, emphasizing the ability of this glycoconjugate to impair the oxidative activity of all phagocytes.

Natural killer cells participate in the early defense against Leishmania major infection in mice

In this study the role of natural killer (NK) cells in the course of experimental Leishmania major infection was investigated. NK cells in genetically resistant C57BL/6 mice were depleted by in vivo administration of anti-asialo-GM1 or anti-NK1.1 antibodies. A marked exacerbation of the infection was found in the NK-depleted mice within the first two weeks of infection. Both the local tissue swelling and the number of parasites in the lesions were significantly higher than in normal animals. Lymph node cells taken from infected NK-depleted mice released less interferon-gamma (IFN-gamma) when cultured in vitro. As an alternate approach we have used poly I:C treatment in order to activate NK cell activity in vivo in BALB/c mice, which are genetically susceptible to L. major infection. Poly I:C treatment led to milder symptoms and to a significantly lower parasite burden in the early course of infection. Lymph node cells from infected and poly I:C-treated BALB/c mice released higher amount of IFN-gamma in vitro than cells from control mice. These data show that NK cells are active participants in the non-specific phase of anti-leishmanial activity in the control of parasite multiplication early in the course of L. major infection in mice.

Reconstitution of C.B-17 scid mice with BALB/c T cells initiates a T helper type-1 response and renders them capable of healing Leishmania major infection

C.B-17 scid mice, which were found to be very susceptible to infection with Leishmania major, were reconstituted with various doses of T cells, T plus B cells or unfractionated spleen cells from nonhealer BALB/c mice. All reconstitution protocols, except for the transfer of very high numbers of BALB/c spleen cells, led to a spontaneously healing infection and resistance to reinfection, rather than the lethal, nonhealing infection typical of BALB/c mice. These healing responses were associated with a strong T helper 1 (Th1)-like response characterized by delayed-type hypersensitivity (DTH) responsiveness, but no elevation of serum IgE, and by the production of high levels of interferon-gamma (IFN-gamma), but no interleukin-4 (IL-4) by lymph node and spleen cells after restimulation with antigen in vitro. The development of this Th1 response from BALB/c Th cells requires IFN-gamma during the initial infection period. Treatment of scid mice with a single injection of neutralizing anti-IFN-gamma antibody prior to infection and reconstitution prevented healing and permitted the development of a Th-2 like response as indicated by elevated serum IgE, but no DTH, and by the production of IL-4, but very little IFN-gamma, after antigen stimulation in vitro. As few as 10(4) transferred T cells led to a Th1-like response, suggesting that the IFN-gamma is of host rather than donor origin. The transfer of very high numbers (7.5 x 10(7)) of BALB/c spleen cells overcame the effects of the IFN-gamma and led to the nonhealing infection and cytokine pattern characteristic of BALB/c mice. The enrichment or depletion of B cells from the transferred T cells had no measurable effect upon the development of a healing response in reconstituted scid mice.

Reduced numbers of CD4+ suppressor cells with subsequent expansion of CD8+ protective T cells as an explanation for the paradoxical state of enhanced resistance to Leishmania in T-cell deficient BALB/c mice

Compared to their normal, T-cell competent counterparts, BALB/c mice that have been thymectomized, lethally irradiated, and reconstituted with bone marrow cells (TXB) were found to be resistant to Leishmania major. Even though TXB mice possess less than 30% of the normal number of T cells in their lymphoid organs, they generated a protective immune response that prevented the progressive multiplication of the parasite in the primary cutaneous lesion and its dissemination to distant visceral sites. Studies of TXB mice depleted of residual CD4+ or CD8+ T cells by systemic monoclonal antibody (mAb) treatment showed that this protective immunity depends on a residual, radio-resistant CD8+ T-cell population, and that it develops in the virtual absence of CD4+ T cells. This immune response can be negated by an infusion of CD4+ T cells from normal susceptible donors, provided that the donor cells are infused before the recipients' response is generated. It is therefore apparant that TXB BALB/c mice are more resistant than T-cell competent BALB/c mice because the former mice lack a threshold number of CD4+ suppressor T cells necessary to down-regulate the induction and expansion of CD8+ protective T cells.

Growth and metabolic properties of Bacteroides intermedius in anaerobic continuous culture

Two strains of Bacteroides intermedius BH20/30 and BH18/23, have been grown in anaerobic continuous culture under various conditions for periods up to 54 days. Strain BH20/30 grew over a relatively wide pH range from 5-8 with a maximum at pH 7.0 at a dilution rate (D) of 0.1 h-1 with a glucose limitation, while strain BH18/23 had an optimum between 5.8 and 7.3 and would not grow above and below this range. The maximum growth rate (mu max) for the latter strain was shown to be 0.23 h-1, or a doubling time of 3.0 at the upper limit of pH 7.3. The yield values (Y glucose) for strain BH18/23 reached 187-177 g cells (dry weight) per mole of glucose in the optimum pH range (6.0-7.0) and amino acid analysis of the spent medium indicated that these high values were the results of the combined use of glucose and amino acids; the cultures also exhibited proteolytic activity. The major acid end-products in the same pH range were formate and succinate with lesser concentrations of acetate, isovalerate and fumarate; small amounts of lactate appeared as the cells were stressed at pH values above 7.5 when the culture was 'washing out' of the chemostat. Glucose metabolism appeared to function through the glycolytic pathway in B. intermedius BH18/23 since the glycolytic inhibitors, sodium fluoride and sodium iodoacetate, completely inhibited glucose utilization as did the proton ionophore, gramicidin, and the ATPase inhibitor, N,N1-dicyclohexylcarbodiimide (DCCD). Inhibition by these latter compounds indicated that the saccharolytic Bacteroides utilize proton gradients generated by proton-extruding ATPase (H+/ATPase) to conserve energy.(ABSTRACT TRUNCATED AT 250 WORDS)

Dissemination in cutaneous leishmaniasis. 3. Lymph node involvement

In a study of zoonotic cutaneous leishmaniasis (CL) due to leishmania major in an endemic focus in Saudi Arabia, lymph node enlargement was observed in 66 of 643 patients (10.26%). The epitrochlear lymph nodes were most commonly involved (68%), but cervical (11%), axillary (15%), and inguinal (18%) lymph nodes were also involved. In eight patients (12%), two lymph node areas were involved. The affected lymph nodes were typically solitary, firm, mobile, nontender, only moderately enlarged, and appeared to persist beyond the clinical healing of the associated skin lesions. The results of pathologic and immunopathologic studies carried out on eight lymph nodes obtained from this group of patients supported the leishmanial etiology. Although amastigotes were only demonstrated in two lymph nodes, the leishmanial antigen was found in all eight specimens. The lymph node involvement is another manifestation of dissemination in infection with a dermotropic leishmania. It appears that in some cases, instead of the parasite, it may be the leishmanial antigen that disseminates and produces lymphadenitis.

Elimination of CD4+ suppressor T cells from susceptible BALB/c mice releases CD8+ T lymphocytes to mediate protective immunity against Leishmania

This study examined the capacity of BALB/c mice that had been depleted of T cell subpopulations to generate a protective immune response to Leishmania major. Thymectomized mice were depleted of either L3T4+ (CD4+) T lymphocytes, Ly2+ (CD8+) T lymphocytes, or both, by treatment with appropriate mAbs. It was found that susceptible mice were rendered resistant to Leishmania by an intravenous infusion of anti-L3T4 mAb. These mice generated an immune response that destroyed the parasite in the primary lesion and in visceral metastatic foci. CD4+ cell-depleted mice also acquired a capacity to mount a sustained delayed-type hypersensitivity (DTH) response to parasite antigens, indicating that DTH, per se, is not a disease-promoting mechanism in the susceptible murine host as has been suggested. Depleting BALB/c mice of CD8+, as well as CD4+ T cells, left them highly susceptible to Leishmania infection, thereby indicating that CD8+ lymphocytes are key protective cells. Our results can be interpreted as showing that the susceptibility of BALB/c mice is due to the generation of CD4+ cells that suppress either the generation or expression of CD8+ T cell-mediated antiLeishmania immunity.

Leishmania mexicana: effect of concomitant malaria on cutaneous leishmaniasis. Development of lesions in a Leishmania-susceptible (BALB/c) strain of mouse

Effect of concomitant malaria on cutaneous leishmaniasis. Development of lesions in a Leishmania-susceptible (BALB/c) strain of mouse. Experimental Parasitology 65, 269-276. Symptoms of human leishmaniasis vary greatly, ranging from cryptic infections to cases with fatal sequelae. Factors regulating the severity of the disease are largely undetermined. Malaria coincides geographically with leishmaniasis in many areas and the immunosuppressive effects of malaria are well documented. It is therefore plausible that malaria could enhance the course of concomitant leishmaniasis. Interactions between Leishmania mexicana and Plasmodium yoelii were examined in BALB/c mice. Percentage of blood cells infected with P. yoelii and diameter of footpad lesions caused by L. mexicana were the criteria used to assay for disease severity. L. mexicana and P. yoelii infections were each significantly enhanced in dually infected mice when compared to mice infected with either parasite alone. Mortality rates due to the normally nonlethal P. yoelii were high during concurrent infections.

Involvement of specific Lyt-2+ T cells in the immunological control of experimentally induced murine cutaneous leishmaniasis

The involvement of Lyt-2+ T cells in the immunological control of cutaneous leishmaniasis was assessed by studying the course of the disease in mice in which the number of these cells was reduced by treatment with anti-Lyt-2 monoclonal antibody (mAb). Administration of anti-Lyt-2 mAb exacerbated Leishmania major-induced cutaneous lesions in both genetically resistant and susceptible mice. This effect correlated with a drastic reduction in the number of specific Lyt-2+ T cells generated during infection. These results, together with the observation that resistant mice possess higher numbers of specific Lyt-2+ T cells in lymph nodes draining their lesions than susceptible mice, 3 weeks after infection, indicate that Lyt-2+ T cells also play a role in the immunological control of Leishmania major-induced lesions.