The identification of sandfly species, from an area of Argentina with endemic leishmaniasis, by the PCR-based analysis of the gene coding for 18S ribosomal RNA

The area around Río Blanco, in the Orán department in the north of the Argentinian province of Salta, is endemic for American tegumentary leishmaniasis. In an attempt to facilitate the identification of the Lutzomyia species in this area, sequences of the gene coding for the 18S ribosomal RNA (rRNA) of sandflies caught in a Shannon trap were explored, by a combination of PCR and analysis of restriction-fragment-length polymorphism (RFLP). The products from the PCR, which employed two primers developed specifically for this study (Lu.18S 1S and Lu.18S AR), were cloned into a commercial vector (pGEM-T Easy) so that their nucleotide sequences could be investigated. In the RFLP analysis, the products of single and double digestion with the AfaI and HapII restriction enzymes were separated by electrophoresis in 3% or 4% agarose. Taken together with the results of a morphological investigation of the flies, the resultant DNA fragment patterns were sufficient to identify most of the sandflies caught as Lu. neivai. Although two other species, Lu. cortelezzii and Lu. sallesi, were collected, they were relatively rare and only identified morphologically. A single digestion of the 18S-rRNA gene sequences with AfaI or HapII appeared sufficient and useful for the identification of Lu. neivai from the north of Salta province, and for several other Lutzomyia species.

Immunological correlates of cure in the first American cutaneous leishmaniasis patient treated by immunotherapy in Argentina. A case report

A patient with localized cutaneous leishmaniasis due to Leishmania (Leishmania) amazonensis infection was treated with an antigen containing heat-killed L. (L.) amazonensis promastigotes plus BCG. Expression of T-cell differentiation, memory and senescence receptors markers were analyzed on T cell subpopulations, in order to establish the correlation between the percentages of expression of these receptors and his clinical status, at different stages of his follow up. The following case reports on the achievement of a successful clinical outcome with complete resolution after receiving immunotherapy. A thorough clinical and immunological follow up supporting the healing process of this patient's lesion is presented in detail.

Hydroxymethylnitrofurazone is active in a murine model of Chagas' disease

The addition of a hydroxymethyl group to the antimicrobial drug nitrofurazone generated hydroxymethylnitrofurazone (NFOH), which had reduced toxicity when its activity against Trypanosoma cruzi was tested in a murine model of Chagas' disease. Four groups of 12 Swiss female mice each received 150 mg of body weight/kg/day of NFOH, 150 mg/kg/day of nitrofurazone (parental compound), 60 mg/kg/day of benznidazole (BZL), or the solvent as a placebo. Treatments were administered orally once a day 6 days a week until the completion of 60 doses. NFOH was as effective as BZL in keeping direct parasitemia at undetectable levels, and PCR results were negative. No histopathological lesions were seen 180 days after completion of the treatments, a time when the levels of anti-T. cruzi antibodies were very low in mice treated with either NFOH or BZL. Nitrofurazone was highly toxic, which led to an overall rate of mortality of 75% and necessitated interruption of the treatment. In contrast, the group treated with its hydroxymethyl derivative, NFOH, displayed the lowest mortality (16%), followed by the BZL (33%) and placebo (66%) groups. The findings of histopathological studies were consistent with these results, with the placebo group showing the most severe parasite infiltrates in skeletal muscle and heart tissue and the NFOH group showing the lowest. The present evidence suggests that NFOH is a promising anti-T. cruzi agent.

Evaluation of high efficiency gene knockout strategies for Trypanosoma cruzi

Background

Trypanosoma cruzi, a kinetoplastid protozoan parasite that causes Chagas disease, infects approximately 15 million people in Central and South America. In contrast to the substantial in silico studies of the T. cruzi genome, transcriptome, and proteome, only a few genes have been experimentally characterized and validated, mainly due to the lack of facile methods for gene manipulation needed for reverse genetic studies. Current strategies for gene disruption in T. cruzi are tedious and time consuming. In this study we have compared the conventional multi-step cloning technique with two knockout strategies that have been proven to work in other organisms, one-step-PCR- and Multisite Gateway-based systems.

Results

While the one-step-PCR strategy was found to be the fastest method for production of knockout constructs, it does not efficiently target genes of interest using gene-specific sequences of less than 80 nucleotides. Alternatively, the Multisite Gateway based approach is less time-consuming than conventional methods and is able to efficiently and reproducibly delete target genes.

Conclusion

Using the Multisite Gateway strategy, we have rapidly produced constructs that successfully produce specific gene deletions in epimastigotes of T. cruzi. This methodology should greatly facilitate reverse genetic studies in T. cruzi.

Serological evaluation of specific-antibody levels in patients treated for chronic Chagas' disease

Serological tests are the main laboratory procedures used for diagnosis during the indeterminate and chronic stages of Chagas' disease. A serological regression to negativity is the main criterion used to define parasitological cure in treated patients. The aim of this work was to monitor the individual specificities of antibody levels for 3 years posttreatment in 18 adult patients. Conventional serological techniques (hemagglutination assays and enzyme-linked immunosorbent assay [ELISA]) were modified by using recombinant antigens to detect early markers of treatment effectiveness. For this purpose, serum samples were taken before and during treatment and every 6 months after treatment for at least 3 years. When hemagglutination assays were used, a decrease in antibody levels was observed in only one patient. When ELISA with serum dilutions was used, antibody clearance became much more apparent: in 77.7% (14/18) of the patients, antibody titers became negative with time. This was observed at serum dilutions of 1/320 and occurred between the 6th and the 30th months posttreatment. The immune response and the interval for a serological regression to negativity were different for each patient. For some of the recombinant antigens, only 50% (9/18) of the patients reached the serological regression to negativity. Recombinant antigen 13 might be a good marker of treatment effectiveness, since 66.6% (six of nine) of the patients presented with an early regression to negativity for specific antibodies to this antigen (P = 0.002).

Trypanosoma cruzi: Infectivity modulation of a clone after passages through different hosts

Although Trypanosoma cruzi virulence can be modified through passages in vivo or long-term in vitro culture, the mechanisms involved are poorly understood. Here we report modifications in the infectivity of a T. cruzi clone after passages in different hosts without detectable changes in parasite genetic patterns. A clone was obtained from a T. cruzi IIe isolate and showed to be less virulent than the original isolate (p<0.05). This clone was enzymatically similar to the original isolate as shown by multilocus enzyme electrophoresis. Infection of this clone was compared by successive passages in mice and guinea pigs. The mouse-passaged subline became more virulent for both host species compared to the guinea pig-passaged subline (p<0.05). The clone line displayed similar random amplified polymorphic DNA patterns before and after passages in different hosts suggesting that alterations in virulence could be a result of a differential expression of virulence factors.

Furoxan derivatives as cytotoxic agents: preliminary in vivo antitumoral activity studies

Furoxan derivatives with in vitro cytotoxic activity were investigated as antitumoral agents in vivo. The compounds were tested in murine models of both CCRFS-180 II sarcoma and mammary adenocarcinoma. Two of the furoxan derivatives considered here, 3-formyl-4-phenyl-1,2,5-oxadiazole N2-oxide and 3-carbonitrile-4-phenyl-1,2,5-oxadiazole N2-oxide, present in vivo antitumoral activity. They were able to produce more than 90% of tumoral necrosis under the experimental protocol of administration and posology employed. NO-releasing capacity of furoxans may explain the anti-neoplastic activity of these compounds.

High prevalence of congenital Trypanosoma cruzi infection and family clustering in Salta, Argentina

OBJECTIVE

Trypanosoma cruzi, the causative agent of Chagas' disease, is transmitted mainly by insect vectors, but congenital and transfusion-borne infections occasionally occur. The factors that are involved in transmission from mother to offspring are not well understood. The objective of this study was to study the presence of T cruzi infection in children who were born to infected mothers and in the children's siblings to evaluate the epidemiologic risk factors associated with congenital transmission of Chagas' disease.

METHODS

Congenital T cruzi infection was studied in 340 children who were born to chronically infected mothers in Salta, Argentina. Infection was detected in 31 children, who were selected for additional study as infected index cases (IIC). Of the 309 noninfected children, 31 were taken as noninfected index cases (NIIC). We compared the prevalence of congenital T cruzi transmission in the remaining siblings of the IIC and NIIC. Data and blood samples were collected in house-to-house visits. Diagnosis of infection was established mainly by serologic methods, indirect hemmagglutination, and enzyme-linked immunosorbent assay.

RESULTS

The prevalence was 31.4% (32 of 102 children) for IIC siblings, whereas no infected siblings were found in families with NIIC (0 of 112). Clustering of congenital infection was found in 14 families, in which >1 child was infected. Second-generation congenital transmission (from grandmother to mother to newborn) was established in 4 families. The association among low weight at birth, prematurity, and congenital transmission was highly significant. An important observation was the absence of pathologic findings in a high proportion of infected children. The detection of asymptomatic infections was a consequence of population screening, as opposed to hospital-based diagnosis, for which symptomatic cases predominate. Congenital transmission was associated with the geographic origin of mothers: women from areas where insect vectors proliferate were less likely to give birth to infected offspring than women from areas under active vector control.

CONCLUSIONS

Siblings of an infant infected with T cruzi are at high risk for infection themselves and, even in the absence of symptoms, should also be screened for infection. The findings of family clustering of infection and of second-generation congenital infection in vector-free areas suggest that new modalities of transmission, other than classic vector-borne spread, may occur both in endemic and in nonendemic areas.

Comparative efficacies of TAK-187, a long-lasting ergosterol biosynthesis inhibitor, and benznidazole in preventing cardiac damage in a murine model of Chagas' disease

We carried out a comparative study of benznidazole and TAK-187, a long-lasting ergosterol biosynthesis inhibitor, with a murine model of Chagas' disease. The results indicated that TAK-187 was more effective than benznidazole in preventing Trypanosoma cruzi-induced cardiac damage in experimental animals.

Chagas disease in rural areas of Chaco Province, Argentina: epidemiologic survey in humans, reservoirs, and vectors

We studied the seroprevalence of antibodies against Trypanosoma cruzi in the human population along with domiciliary infestation by triatomine bugs in an area endemic for Chagas disease in the Chaco Province of Argentina. In addition, we carried out parasitologic surveys in patients, dogs, wild mammals, and vectors. The mean seroprevalence in humans was 27.81% (109 of 392) and 24.14% (63 of 261) in 1-15-year-old children. The minimum domiciliary infestation rate was 13.33%, with certain areas reaching 53.85%. The prevalence was 15.09% (16 of 106) in dogs and 35.71% (10 of 28) in opossums. Infection with T. cruzi was detected in 30.10% (59 of 196) of the Triatoma infestans tested. Compared with nationwide studies, our data suggest that 1) there are zones requiring immediate sanitary action, and 2) nationwide estimates are based on very heterogeneous epidemiologic situations. This heterogeneity emphasizes the importance of in-depth studies of restricted areas to provide additional information for a better understanding of the present status of Chagas disease in Argentina.

Canine infection and the possible role of dogs in the transmission of American tegumentary leishmaniosis in Salta, Argentina

Some Leishmania species affect humans in two principal forms: visceral and cutaneous leishmaniosis (CL). Several studies have identified dogs as the main reservoirs of the visceral leishmaniosis (VL) caused by Leishmania infantum. The purpose of this work was to carry out a survey of the canine population associated with human cases of American tegumentary leishmaniosis (ATL), in order to establish the clinical, parasitological, serological and immunological characteristics of the canine disease, in an endemic region for both ATL and Chagas' disease in the province of Salta, in northwestern Argentina. Two hundred and eight dogs from the endemic area were examined and 41 (19.7%) of them presented lesions compatible with leishmaniosis. In order to investigate the presence of antibodies against Leishmania spp. and Trypanosoma cruzi, sera were screened by ELISA using two complex antigens from these parasites and, because of cross-reactions between them, a specific antigen for diagnosis of T. cruzi infection. Sixty-two (29.8%) of 208 dogs were positive for the complex antigen F45 from Leishmania and 50 (24%) were positive for the complex antigen F105 from T. cruzi. Nine dogs (4.3%) were positive for the specific Ag163B6-cruzipain suggesting that these dogs were truly infected with T. cruzi. Furthermore, three of these nine dogs presented Leishmania sp. in their skin lesions and therefore were considered as infected by both, T. cruzi and Leishmania parasites. The prevalence of Leishmania infection detected by lesions and/or positive serology was 27.4% (57/208). On the basis of previous observations regarding the clustered appearance of human ATL, the dog population was divided into two groups: zone A, dogs living within a 100 m radius from houses with human cases, and zone B, dogs living beyond this limit. The prevalence of ATL in dogs was significantly higher in zone A (34.6%) than in zone B (7.3%), suggesting a strong correlation between canine and human cases. The average time required for a parasitological diagnosis by microscopy was six times longer for dog samples than human ones, and the average number of parasites per 100 microscopic fields was 14-fold lower in canine samples. The high prevalence of Leishmania infection and the close association with human cases, demonstrated that dogs are a very susceptible host for Leishmania infection, but the scarcity of parasites in their lesions suggests that they may not be the main reservoir of the parasite in this endemic area.

Relationship between long-term resistance to Trypanosoma cruzi and latent infection, examined by antibody production and polymerase chain reaction in mice

Trypanosoma cruzi infections persist for the lifetime of humans and laboratory animals as either latent or pathogenic parasitism. Mice inoculated with a nonpathogenic, attenuated strain (TCC) display resistance against virulent challenge, with a strong control of parasitemia and protection against tissue lesions for more than 12 mo. Three main approaches were used to test whether protection by TCC inocula is based on a latent infection or on a "sterile" immunological memory: curative Benznidazole (Bzl) treatment, serological reactions, and detection of infection by polymerase chain reaction (PCR). If resistance is maintained in the absence of infection, it should not be reduced by Bzl treatment and TCC-inoculated animals should not maintain long-term serological or PCR reactivity. The Bzl treatment after TCC inoculations did not reduce, after periods of up to 420 days, TCC-induced resistance to challenge. But TCC inocula given during Bzl treatment conferred short-term, but not long-term. protection. Maintenance of high antibody levels and protection were better in the virulent Tulahuen (TUL) strain than in the attenuated TCC strain infections, and trypomastigote inocula of either strain were better inducers of antibodies and resistance than epimastigotes. PCR detection of T. cruzi DNA was positive in almost all TUL strain-inoculated animals and negative in immunocompetent animals inoculated with TCC epimastigotes, although high numbers of TCC trypomastigotes produced persistent PCR signals of infection in newborn BALB mice. Thus, 2 polar models were developed, where latent infection by TCC was either demonstrated or excluded. In both, resistance to virulent challenge was maintained during long periods. But late declination of antibody titers (>200 days) and resistance to challenge (>350 days) was observed in animals displaying clearance of all signals of infection.

Force of infection and evolution of lesions of canine tegumentary leishmaniasis in northwestern Argentina

A clinical-serological follow-up was carried out in a canine population in endemic foci of Leishmania braziliensis spread in northwestern Argentina. Each dog was studied in at least two visits, 309+/-15 days (X+/-SE) apart. Some initially healthy dogs (n=52) developed seroconversion or lesions. The clinical evolution of the disease in dogs resembles in many aspects the human disease. Similarities include the long duration of most ulcers with occasional healing or appearance of new ones and the late appearance of erosive snout lesions in some animals. Yearly incidence rates of 22.7% for seroconversion and of 13.5% for disease were calculated as indicators of the force of infection by this parasite upon the canine population.

Studies on the virulence and attenuation of Trypanosoma cruzi using immunodeficient animals

Tissue invasion and pathology by Trypanosoma cruzi result from an interaction between parasite virulence and host immunity. Successive in vivo generations of the parasite select populations with increasing ability to invade the host. Conversely, prolonged in vitro selection of the parasite produces attenuated sublines with low infectivity for mammals. One such subline (TCC clone) has been extensively used in our laboratory as experimental vaccine and tested in comparative experiments with its virulent ancestor (TUL). The experiments here reviewed aimed at the use of immunodeficient mice for testing the infectivity of TCC parasites. It has not been possible to obtain virulent, revertant sublines by prolonged passaged in such mice.

[The transmission de Chagas disease in Salta and the detection of congenital cases]

Data on the prevalence of Trypanosoma cruzi infection is presented for the province of Salta, Argentina. Special emphasis is given to the detection of congenital transmission and to the economic benefits of preventing Chagas' disease. Seroepidemiological data obtained from 20 year old army draftees revealed a reduction, from 22.7 to 11.11% between 1964 and 1985. In university students, a rate of 0.96% was found in 1998. Surveys carried out during 1996 showed that more than 15% of the pregnant women analyzed carried T. cruzi infection, particularly in the north of the province. This situation brings about a high risk of appearance of congenital cases and represents an opportunity to test the most adequate strategies for detection. By applying systematically microhematocrit, hemoculture and PCR methods, to umbilical chord blood, an increase in the early detection of congenitally infected babies is being achieved. In 1992-94, very high seroprevalence rates of infection were found among indians of the Chaco region of Salta. The overall rate was 37%, but there were 5 localities where more than 54% of the population was infected. These numbers indicate that, in vast areas of the provincial territory, fight against vector bugs must not merely consist of surveilance activities, but rather of renewed spraying attacks. The fight must include control of pregnant women and blood banks. An economic analysis of the economic return, calculated only for spraying activities and for the Department of Anta (Salta), indicated a net present value of over 7 million dollars and an internal rate of return exceeding 60%.

Synthesis and antitrypanosomal evaluation of E-isomers of 5-nitro-2-furaldehyde and 5-nitrothiophene-2-carboxaldehyde semicarbazone derivatives. structure-activity relationships

Several novel semicarbazone derivatives were prepared from 5-nitro-2-furaldehyde or 5-nitrothiophene-2-carboxaldehyde and semicarbazides bearing a spermidine-mimetic moiety. All derivatives presented the E-configuration, as determined by NMR-NOE experiments. These compounds were tested in vitro as potential antitrypanosomal agents, and some of them, together with the parent compounds, 5-nitro-2-furaldehyde and 5-nitrothiophene-2-carboxaldehyde semicarbazone derivatives, were also evaluated in vivo using infected mice. Structure-activity relationship studies were carried out using voltammetric response and lipophilic-hydrophilic balance as parameters. Two of the compounds (1 and 3) displayed the highest in vivo activity. A correlation was found between lipophilic-hydrophilic properties and trypanocidal activity, high R(M) values being associated with low in vivo effects.

A cost-benefit analysis of Chagas disease control in north-western Argentina

Chagas disease has been controlled in the Department of Anta, Province of Salta, Argentina, through a series of vector control interventions beginning in 1983. Based on data from this programme, together with estimates of the value of benefits accruing to the programme due to avoidance of new cases of Chagas disease, we present an analysis of costs and benefits of the vector control interventions. Under all assumptions, the interventions have been highly profitable from a societal point of view, with an internal rate of return in excess of 60%. The net present value of benefits accruing to the programme is estimated to be above US$7 million.

Trypanosoma cruzi: effect of immunization on the risk of vector-delivered infection in guinea pigs

The protective effect of experimental immunization was studied in guinea pigs exposed to vectorial infection by Trypanosoma cruzi. Immunized animals received an inoculum of live-attenuated T. cruzi epimastigotes into a granuloma previously induced by Freund's complete adjuvant in the hind footpad. Seven days later, a delayed-type hypersensitivity reaction was triggered by reinjection of the parasites in the front footpad. The animals were then placed in Triatoma infestans-colonized corrals and exposed to vectorial T. cruzi transmission of the parasite for up to 200 days. The effectiveness of this immunizing protocol was controlled in terms of the number of bites necessary for infection (NBNI) in immunized as compared with control animals. Periodic entomological census allowed for the determination of vector biting and infection rates and the calculation of NBNI. Although this measurement was quite variable between yards, an overall average of 4,973 bites was enough to infect a control guinea pig in 4 separate experiments. The corresponding figure for the experimental group was 21,307 bites, implying that immunized animals could resist a 4.28-fold increase (range: 1.99-8.32) in the number of vector bites before becoming infected.

Immunogenicity of the recombinant SAPA protein of Trypanosoma cruzi for mice

The humoral and cellular immune responses induced by the recombinant SAPA (shed acute phase antigen) of Trypanosoma cruzi were studied in mice and correlated with the immunologic control of parasitemia. The immunizing schedule used consisted of 2 weekly injections of 50 micrograms glutathione-S-transferase (GST)-SAPA in Freund's adjuvant. Specific alpha GST-SAPA antibodies were detected by enzyme-linked immunosorbent assay 1 wk after each antigen dose, the concentration of antibodies after the second injection being 30-fold higher than after the first. Immediate- (ITH) and delayed-type hypersensitivity (DTH) reactions were observed as footpad swelling after injecting 50 micrograms GST-SAPA in preimmunized mice as compared to naive controls. Adoptive transfer experiments indicated that these cutaneous reactions were mediated by lymphoid cells and not by serum. Both humoral and cellular responses were specific for the GST-SAPA antigen and did not cross-react with either the GST or the recombinant GST-1 T. cruzi antigen. Immunized mice that had developed high levels of antibody and DTH reaction to GST-SAPA were able to control the level of parasitemia after challenge with 10(3) blood trypomastigotes. The levels of parasitemia obtained were lowered to about 1/3 (P < 0.05) and mortality at day 60 was reduced from 67 to 25% (P = 0.085). Comparison of this immunizing method with other schedules involving more injections or higher antigen doses indicates that control of parasitemia can be obtained with low amounts of antigen and seems to be associated with the development of DTH.

Complete immunization against Trypanosoma cruzi verified in individual mice by complement-mediated lysis

Experimental systems to assay immunity against Trypanosoma cruzi usually demonstrate partial resistance without excluding the establishment of sub-patent infections in protected animals. To test whether Swiss mice immunized with attenuated parasites might develop complete resistance against virulent T. cruzi, experiments were performed involving challenge with low numbers of parasites, enhancement of local inflammation and the combination of natural and acquired resistance. Absence of infection was established after repeated negative parasitological tests (including xenodiagnosis and hemoculture), and lack of lytic antibody was tested by complement mediated lysis. Immunization with 10(7) attenuated epimastigotes conferred protection against the development of high levels of parasitemia after challenge with Tulahuen strain, but was unable to reduce the number of infected animals. However, when a strong, delayed-type hypersensitivity reaction was triggered at the site of infection by injecting a mixture of virulent and attenuated T. cruzi, a significant proportion of immunized animals remained totally free of virulent infection. The same result was obtained when the immunization experiment was performed in four month old Swiss mice, displaying a relatively high natural resistance and challenged with wild, vector-borne parasites. These experiments demonstrate that complete resistance against T. cruzi can be obtained in a significant proportion of animals, under conditions which replicate natural, vector delivered infection by the parasite.

Field trial of vaccination against American trypanosomiasis (Chagas' disease) in domestic guinea pigs

Domestically bred South American guinea pigs received 3 to 5 immunizing intradermal inocula of 28 X 10(6) live attenuated Trypanosoma cruzi epimastigotes (TCC strain) per kg. These inocula were unable to produce patent infections or to propagate through vectors. Groups of experimental and control guinea pigs were exposed to natural T. cruzi infection in a field yard for periods of up to 551 days. Xenodiagnoses were applied periodically to all animals. This showed that the incidence of natural T. cruzi infection was significantly lowered at various periods post-exposure. The final proportion of infected animals was 39% (20/51) among vaccinees vs. 63% (32/51) among controls (P less than 0.02). The protective effect was exerted particularly upon males and lasted for over a year in one experimental series (infection in 1/7 vaccinees vs. 6/7 controls, P = 0.014). Vaccination reduced vector transmission rates from 38% to 18% (P less than 0.001). These results agree with previous laboratory experiments in showing a partial resistance which does not eliminate residual T. cruzi infection. However, the field work indicates that even this kind of resistance may have epidemiological impact, reducing both the number of reservoirs spreading the disease and the rate of vector transmission.

Trypanosoma cruzi culture used as vaccine to prevent chronic Chagas' disease in mice

The development of chronic pathology in mice at 2 to 10 months after inoculation of 10(2) T. cruzi trypomastigotes can be prevented by preimmunization with live, attenuated culture parasites (strain TCC). Swiss mice received one or three immunizing inoculations of 10(6) TCC organisms and were challenged with 10(2) Tulahuén blood trypomastigotes. Control groups received only the immunizing or the challenge inoculations. Immunized groups as compared with nonimmunized controls had lower mortality rates at 2 months postchallenge (9% versus 23%; P = 0.059), lower early peaks of parasitemia, lower percentages of positive xenodiagnoses at 5.5 months (40 versus 80%; P = 0.061), and lower incidences of tissue lesions in the skeletal muscle (P less than 0.005) at 2,6, and 10 months postchallenge. Tissue lesions in the heart and smooth muscle were also reduced, reaching statistical significance after 10 months (P less than 0.02). Chronic pathology parameters were never enhanced in preimmunized groups. In spite of the putative role that autoimmunity may play in the development of chronic chagasic lesions, the preventive effect of vaccination is readily exerted upon the chronic murine model of Chagas' disease.

Side effects of immunization with liver attenuated Trypanosoma cruzi in mice and rabbits

Immunity against lethal, bloodstream forms of Trypanosoma cruzi was achieved in mice by preinoculation of approximately equal to 10(5) culture epimastigotes of an attenuated T. cruzi strain (TCC). The risks of TCC inoculation in terms of pathogenicity or eventual increase in virulence of TCC progeny were evaluated. No pathogenic parasites could be selected from TCC progeny by either mouse, triatome, or culture passages. Immunizing doses of live TCC did not induce in adult mice alterations resembling chronic Chagas' disease, as judged by patterns of mortality, tissue damage, autoantibodies, or parasite recovery. On the basis of the same criteria, However, a remarkable similarity could be established between the disease caused in mice by inoculation of low numbers (10(2)) of pathogenic trypomastigotes and human chronic Chagas' disease. Although patent parasitemias were never revealed in fresh blood mounts obtained from TCC-inoculated mice, a few hemocultures and xenodiagnoses gave positive results, particularly soon after inoculations at birth. The parasites recovered by either method remained in the attenuated, epimastigote stage. In rabbits, no local lesions, fever, weight loss, or histopathological alterations were detected after subcutaneous inoculation of 10(7) TCC organisms, although one fifth of the animals yielded positive hemocultures of epimastigotes. The contrasting host response to cultured epimastigotes as compared with blood trypomastigotes indicates that, in experimental Chagas' disease, immunoprotection is not necessarily associated with immunopathology.

Active immunization against murine radiation-induced leukemia using a sarcoma virus pseudotype

Immunization of C57BL/Ka mice against the radiation leukemia virus (Rad LV) markedly reduced their susceptibility to development of leukemia after X-radiation. The active immunogen used consisted of a sarcoma virus pseudotype of Rad LV which induces regressing sarcomas in young adult mice. These immunized animals were challenged with four weekly 160-rad X-ray exposures. The appearance of lymphomas and leukemias resulting from such irradiation was delayed and their incidence significantly decreased. These results indicate that oncornavirus immunization may be used to reduce the incidence of murine leukemias which are triggered by a physical agent.

Enhanced growth of syngeneic Moloney sarcoma with decreased immunity in the regressors

S.c. cellular transplants of MS tumours have a high incidence of rejection in adult BALB/c mice, which can then be used as syngeneic regressors. When these tumours were inoculated within a glass cylinder which had been implanted s.c. in BALB/c mice 2 days earlier, 51% of the animals died with progressively growing tumours, compared with 2% in animals which had received the same inoculum directly s.c. This experimental model demonstrates tumour enhancement in a syngeneic system, and duplicates what has been previously reported in two different allogeneic tumour-host combinations, where it was demonstrated that immunological enhancement was operating, since the addition of either progressor serum or soluble tumour antigen significantly increased tumour incidence. For the purpose of investigating whether the glass cylinder model could also modify the immune response of the host to a second tumour challenge, a leukaemia virus known to crossreact with MS was used. Regressors were challenged i.p. with a lethal dose of a leukaemia virus, PLLV. Regressors bearing a glass cylinder showed a 22% survival rate which was significantly lower than that of the s.c. inoculated regressors (71%). This decrease in cross-immunity suggests that the artificially constructed privileged site created by the glass cylinder, by conditioning for tumour enhancement, also decreases immunological memory.

Murine sarcoma virus pseudotypes used as immunogens against viral and chemical oncogenesis

The purpose of this study was to develop an animal system of protective immunity against oncornaviruses and to test whether such immunization had an inhibitory effect upon chemical sarcomagenesis. Several murine sarcoma virus (MSV) pseudotypes were used as immunogens and tested against themselves, against other pseudotypes, against leukemogenesis by their helper viruses, and against sarcomagenesis by 3-methylcholanthrene. Five MSV pseudotypes were obtained by rescuing complete MSV from MSV-genome carrier, nonproducer hamster tumor cells, using five different leukemia viruses as helpers. The immunogenic properties of these pseudotypes could be specified on the basis of the following observations. 1) They all induced sarcomas in newborn mice and regressing sarcoma nodules in young adult mice. After regression, most mice remained free of neoplastic disease, but some developed sarcoma or leukemia relapses. 2) They had an individual host range pattern, usually determined by the helper virus, as tested by inoculation of a constant virus dose in BALB/c, C57BL/Ka, and Swiss mice. 3) They were all immunogenic, in the sense that the first virus inoculation prevented sarcoma induction by a second challenge, either viral or cellular. 4) They were cross-reactive in vivo, one pseudotype immunizing against another, in the combinations tested. 5) They were able to immunize against leukemogenesis induced by their helper viruses. This was shown by prevention of leukemic deaths by Rauscher and Friend viruses, by a slight prolongation of survival after challenge with the Precerutti-Law leukemia virus, and by inhibition of splenomegaly by Moloney leukemia virus. In a second stage of the study, we investigated whether immunization with any of the MSV psuedotypes had an inhibitory effect upon sarcomagenesis induced by near-threshold doses of 3-methylcholanthrene. The incidence of these sarcomas was essentially the same in virus-immunized and control mice. It was concluded that immunizing procedures able to prevent sarcomagenesis when the inducer is a virus did not have any consistent preventive effect when the inducer was a chemical.