Functional analysis of the murine T lymphocyte immune response to a protozoan parasite, Leishmania tropica

The results presented in this review summarize a seirs of experiments designed to characterize the murine T cell imune response to the protozoan parasite Leishmania tropica. Enriched T cell populations and T cell clones specific for L. tropica antigens were derived from lymph nodes of primed mice and maintained in continous culture in vitro. These T lymphocytes were shown (A) to express the Lyt 1+ 3- cell surface phenotype, (B) to proliferate specifically in vitro in response to parasite antigens, together with a source of irradiated syngeneic macrophages, (C) to transfer antigen-specific delayed-type hypersensitivity (DTH) responses to normal syngeneic mice, (D) to induce specific activation of parasitized macrophages in vitro resulting in the destruction of intracellular parasites, (E) to provide specific helper activity for antibody responses in vitro in a hapten-carrier system. Protection studies using these defiened T cell populations should allow the characterization of parasite antigen(s) implicated in the induction of cellular immune responses beneficial for the host.

Interactions between Leishmania mexicana mexicana promastigotes and amastigotes and murine peritoneal macrophages in vitro

Unstimulated adherent mouse peritoneal cells were cultured in vitro and infected with equal numbers of a single strain of Leishmania m. mexicana amastigotes (AM), virulent promastigotes (VP), avirulent promastigotes (AVP) and fixed promastigotes (FP). Duplicate May-Grünwald-Giemsa stained coverslips were examined at time intervals up to 13 days. By 3 hr post infection, the number of macrophages containing parasites varied between 60.5% (VP) and 84% (AM) for macrophages exposed to living parasites, compared to 6.5% for macrophages exposed for FP. However, variable numbers of parasites showed degenerative changes by 3 hr, and the number of macrophages containing morphologically intact parasites varied significantly between cells infected with AM (84%) and those infected with VP (42%) or AVP(40%). The mean number on intacte parasites/macrophage also differed significantly between AM-infected cells and living or fixed promastigotes-infected cells. Quantitation of intact and degenerated parasites indicated parasite multiplication, as well as destruction, in VP-infected cells and parasite survival and multiplication in AM-infecte monolayers; in contrast no evidence of parasite multiplication was seen in AVP-infected cells. Changes in the mono layer itself (cell loss and macrophage vacuolization) were also evaluated. These results suggest that crucial events determining the outcome of infection occur in the host-parasite relationship during the fist 24 hours of infection. These events are apparently influenced not only by parasite or host strain but by environmentally induced variation within a given strain.

Treatment of acute experimental schistosomiasis

A model of acute schistosomiasis of the mouse was used to observe whether curative treatment would be followed by an enhancement of the hepatic and splenic lesions, as a consequence of the massive destruction of worms and eggs within the portal system. Mice infected with 50 cercariae of Schistosoma mansoni were treated with both oxamniquine and praziquantel on the 50th day of infection and submitted to a sequential histologic examination from the 2nd to the 45th day after treatment. Although severe focal lesions due to dead and disintegranting worms were present in the livers of the treated animals, no aggravation of the general changes (reative hepatitis and splenitis, or periovular granulomas) was seen in comparison with a control non-treated group. Of 50 animals treated during the acute phase of schistosomiasis only one died espontaneously, while 16 ou of 30 infected controls died before the end of the experiment. The present investigation indicates that curative treatment during the acute phase of schistosomiasis does not enhance previous lesions at first and results in progressive disappearance of the lesions starting six days following chemotherapy.

Distinct ultrastructural aspects in different biopsies of a single patient with diffuse cutaneous leishmaniasis

The authors investigated the relation between parasites and host-cells in active and regressed lesions of a patient with diffuse cutaneous leishmaniasis, evaluating the frequency of different cell types, and the location and integrity of amastigotes. No correlation was found between parasite integrity and size of parasitophorous vacuoles. They observed ultrastructural findings characterizing a cell mediated immune response: macrophages lysis, parasitic destruction inside macrophages, close contact between parasitized macrophages and lymphocytes and between parasites and lymphocytes, lymphocytic infiltration and fibrosis. They suggest that in DCL there is a limited cellular immune response, although insufficient to control infection.

Effect of the host specific treatment in the phagocytosis of Trypanosoma cruzi blood forms by mouse peritoneal macrophages

Single doses of drugs active aginst Trypanosoma cruzi (megazol, nifurtimox and benznidazole) induce a rapid clearence of the blood parasites in experimentally infected mice. Furthermore, the in vitro phagocytosis and intracellular destruction by mouse peritoneal macrophage of blood forms collected from the treatment animals is strongly enhanced as compared with parasites from untreated controls. The uptake of the blood forms by macrophages is significantly higher with megazol than with benznidazole and nifurtimox, a finding that concurs with data showing that megazol is also the most active compound in the living host. The possibility that macrophages participate in a synergic effect between the host immune response and chemotherapeutic effect is discussed.

Immunopathology of American cutaneous leishmaniasis

American mucocutaneous leishmaniasis is a granulomatous disease clinically characterized by ulcerated skin lesions that can regress spontaneously. A small percentage of the affected individuals can however develop a severe destruction of the nasal, oral, pharyngeal and/or laryngeal mucous membranes many years after the healing of the primary lesion. The human immune response to the infection and the possible mechanisms underlying the pathogenesis of the disease, determining either the self-healing or the development of chronic and destructive mucosal lesions, are discussed.

Ecoepidemiological aspects of american cutaneous leishmaniasis in the state of São Paulo, Brazil

The aim of this study is to review some of the ecoepidemiological aspects of american cutaneous leishmaniasis (ACL) in the state of São Paulo, Brazil. During the first half of this century ACL occured in São Paulo, predominantly on the bank of the Tietê river, where there were railroad constructions and there was inevitable contact between and forested areas. Man's activities resulted in a drastic reduction of the forested regions of the state and molded the present landscape found in São Paulo, which brought a gradual change in the epidemiology of ACL during this century. Currently ACL can be considered as an endemic disease. Nowadays, ACL is found in different regions of São Paulo state, and is no longer limited to the bank of the Tietê river. The disease occurs in all age groups and sexes. Lack of knowledge about wild reservoir hosts of Leishmania (V.) braziliensis has simulated speculation about the possible role played by domestic animals (dogs and equines). Man's activities also favoured Lutzomyia intermedia a sandfly species which can clearly thrive in changed environments L. (V.) braziliensis continues to be transmitted, even after decades of forest destruction in São Paulo.

The dermal leishmaniases of Brazil, with special reference to the eco-epidemiology of the disease in Amazonia

Six species of Leishmania are at present known to cause cutaneous and/or mucocutaneous leishamniasis in Brazil, and they are all to be found in the Amazon region of this country. The eco-epidemiology of each is discussed, with the observation that the Amazonian leishmaniases are all zoonoses, with their source in silvatic mammals and phlebotomine sandfly vectors. With man's destruction of the natural forest in southern Brazil, some sandfly species have survived by adapting to a peridomestic or domiciliary habitat in rural areas. Some domestic animals, such as dogs and equines are seemingly now involved in the epidemiology of the disease. No such process has yet been reported in the Amazon region, but may well take place with the continuing devastation of its forest.

Current concepts of snail control

Schistosomiasis control was impossible without effective tools. Synthetic molluscicides developed in the 1950s spearheaded community level control. Snail eradication proved impossible but repeated mollusciciding to manage natural snail populations could eliminate transmission. Escalating costs, logistical complexity, its labour-intensive nature and possible environmental effects caused some concern. The arrival of safe, effective, single-dose drugs in the 1970s offered an apparently better alternative but experience revealed the need for repeated treatments to minimise reinfection in programmes relying on drugs alone. Combining treatment with mollusciciding was more successful, but broke down if mollusciciding was withdrawn to save money. The provision of sanitation and safe water to prevent transmission is too expensive in poor rural areas where schistosomiasis is endemic; rendering ineffective public health education linked to primary health care. In the tropics, moreover, children (the key group in maintaining transmission) will always play in water. Large scale destruction of natural snail habitats remains impossibly expensive (although proper design could render many new man-made habitats unsuitable for snails). Neither biological control agents nor plant molluscicides have proved satisfactory alternatives to synthetic molluscicides. Biologists can develop effective strategies for using synthetic molluscicides in different epidemiological situations if only, like drugs, their price can be reduced.

Trypanosoma cruzi strains and autonomic nervous system pathology in experimental chagas disease

Lesions involving the sympathetic (para-vertebral ganglia) and para-sympathetic ganglia of intestines (Auerbach plexus) and heart (right atrial ganglia) were comparatively analyzed in mice infected with either of three different strain types of Trypanosoma cruzi, during acute and chronic infection, in an attempt to understand the influence of parasite strain in causing autonomic nervous system pathology. Ganglionar involvement with neuronal destruction appeared related to inflammation, which most of the times extended from neighboring adipose and cardiac, smooth and striated muscular tissues. Intraganglionic parasitism was exceptional. Inflammation involving peripheral nervous tissue exhibited a focal character and its variability in the several groups examined appeared unpredictable. Although lesions were generally more severe with the Y strain, comparative qualitative study did not allow the conclusion, under the present experimental conditions, that one strain was more pathogenic to the autonomic nervous system than others. No special tropism of the parasites from any strain toward autonomic ganglia was disclosed.

Sandfly Lutzomyia longipalpis in a cutaneous leishmaniasis focus in central Colombia

Lutzomyia longipalpis, 15 other species of the genus Lutzomyia, and one species of Brumptomyia were collected in an endemic focus of cutaneous leishmaniasis in a river canyon 450 m above sea-level, in Rio Claro, Antioquia, Colombia. The presence of Lu. longipalpis is associated with the destruction of the primary forest and the development of new farmland and rural settlement in this region. The composition of species identified a different habitat for Lu. longipalpis in Colombia. Lu. yuilli and Lu. longipalpis were predominant (68.26%) followed by Lu. trapidoi, Lu. hartmani, Lu. triramula, Lu. panamensis, Lu. gomezi.

Histopathologic features associated with susceptibility and resistance of biomphalaria snails to infection with Schistosoma mansoni

Resistance and susceptibility of Biomphalaria snails to Schistosoma mansoni sporocysts occur in different degrees. Histopathology reflects these diferences. In a state of tolerance numerous sporocysts in different stages of differentiation are seen in the absence of host tissue reaction. However extensive diffuse and focal proliferation of amebocytes with sequestration and destruction of many parasitic structures appear in resistant snails. Some snails are totally resistant and when exposed to infecting miracidia may never eliminate cercarie. Sequential histopathological examination has revealed that in such cases the infected miracidia are destroyed a few minutes to 24 hr after penetration in the snail. However, B. glabrata that were exposed to S. mansoni miracidia and three moths later failed to shed cercariae, exhibited focal and diffuse proliferation of amebocytes in many organs in the absence of pasitic structures. These lesions were similar to those observed in resistant snails that were still eliminating a few cercariae, with the difference that no recognizable sporocystic structures or remmants were present. Histological investigation carried out in similarly resistant B. tenagophila and B. straminea presented essentially normal histologic structures. Only occasionally a few focal proliferative (granulomatous) amebocytic reactions were seen in ovotestis and in the tubular portion of the kidney. Probably, there are two types of reactions to miracidium presented by totally resistant snails: one would implicate the immediate destruction of the miracidium leaving no traces in the tissues; the other involving late reactions that seem to completely destroy invading sporocysts and leave histological changes.

Immunopathology of cardiomyopathy in the experimental Chagas disease

The mechanisms by which Trypanosoma cruzi causes cardiomyopathy and induces neuronal destruction are discussed in this paper. The results suggest that autoimmunity in the chronic phase is the main cause of the progressive cardiac destruction, and that autoreactivity is restricted to the CD4+ T cell compartment. During the acute phase, the neuronal and cardiac fiber destruction occurs when ruptured parasite nests release T. cruzi antigens that bind to the cell surface in the vicinity which become targets for the cellular and humoral immune response against T. cruzi. The various factors involved in the genesis of autoimmunity in chronic T. cruzi infection include molecular mimicry, presentation of self-antigens and imbalance of immune regulation.

Action of pentoxifylline on experimental cutaneous leishmaniasis due to Leishmania (Leishmania) amazonensis

In the animal model of leishmaniasis caused by Leishmania (Leishmania) amazonensis there is a complex mechanism of the host-parasite interaction. The present study was performed to interfere with the inflammatory reaction to the parasites, through immune modulation. Female C5BL/6 isogenic mice were used, some of which were inoculated on the right ear and others on the right footpad with 3.10(6) stationary phase promastigotes of the MHOM/BR/PH8 strain of L. (L.) amazonensis, and were allocated in three groups: the first received pentoxifylline 8mg/kg every 12 h, since the first day; the second one received the same dose since the 40th day of infection and a control group that did not receive any treatment. All the ears excised were analyzed to determine the variation in weight between both ears and for histopathological analyses. A quantification of the parasites was done using the limiting dilution assay. A significant reduction of the number of parasites, was observed among the animals treated which had an accordingly significant reduction on the weight of the ears. Pentoxifylline reduced the macrophages propensity to vacuolation and induced a more effective destruction of the parasites by these cells. Moreover, the group that began the treatment later did not show the same effectiveness.

Apoptosis as a target for gene therapy in rheumatoid arthritis

Rheumatoid arthritis (RA) is characterized by chronic inflammation of the synovial joints resulting from hyperplasia of synovial fibroblasts and infiltration of lymphocytes, macrophages and plasma cells, all of which manifest signs of activation. All these cells proliferate abnormally, invade bone and cartilage, produce an elevated amount of pro-inflammatory cytokines, metalloproteinases and trigger osteoclast formation and activation. Some of the pathophysiological consequences of the disease may be explained by the inadequate apoptosis, which may promote the survival of autoreactive T cells, macrophages or synovial fibroblasts. Although RA does not result from single genetic mutations, elucidation of the molecular mechanisms implicated in joint destruction has revealed novel targets for gene therapy. Gene transfer strategies include inhibition of pro-inflammatory cytokines, blockade of cartilage-degrading metalloproteinases, inhibition of synovial cell activation and manipulation of the Th1-Th2 cytokine balance. Recent findings have iluminated the idea that induction of apoptosis in the rheumatoid joint can be also used to gain therapeutic advantage in the disease. In the present review we will discuss different strategies used for gene transfer in RA and chronic inflammation. Particularly, we will highlight the importance of programmed cell death as a novel target for gene therapy using endogenous biological mediators, such as galectin-1, a beta-galactoside-binding protein that induces apoptosis of activated T cells and immature thymocytes.