Effect of chagasic sera on the rat isolated atrial preparation: immunological, morphological and function aspects.

An antibody reacting with the plasma membrane of working myocardial cells, skeletal muscle fibres, and endothelial cells (EVI antibody) has been described in the sera of patients with Chagas' disease. In the present study of rat isolated atrial preparations beating in ddifferent media, direct immunofluorescence and ultrastructural immunohistochemical procedures indicate that the antibody can interact with the living tissue, becoming fixed to the plasma membranes. Transmission electronmicroscopy studies also showed the presence of sarcolemmal alterations. These observations suggest a possible pathogenic effect of the EVI antibody. The presence of EVI-positive sera in the beating medium leads to a significant increase in the frequency of contractions; no significant effects of EVI-positive sera in contractile force were seen. The increase in frequency could be prevented by previous treatment with a b-adrenergic blocking agent (MJ-1999), but not by an x-blocker (phentolamine) or by an anti-histamine compound (cyproheptadine). The changes described were observed only in those atrial preparations which were beating in media containing EVI-positive sera. In those atria beating in control media (KR,KR plus normal human serum, KR plus EVI-negative chagasic serum), neither immunological nor morphological or functional changes wersence of EVI-positive chagasic serum diminished atrial stimulation after added norepinephrine. These results suggest the possibility that the EVI antibody may act as a b-adrenergic agonist at the cell plasma membrane level. Such an effect might account for some of the clinical features of chronic Chagas' heart disease.

Immunofluorescent vascular pattern due to EVI antibody of Chagas' disease. Its diagnostic value.

One hundred fifty-six of 1,250 sera from patients with presumed connective tissue and related diseases showed vascular staining on mouse liver cryostat sections when they were routinely checked for antinuclear factor by the indirect immunofluorescence test. In a third of the cases, the vascular immunofluorescent pattern was given by the EVI antibody reacting with the plasma membrane of striated muscle fibers and endothelial cells, as has been recently described to occur in Chagas' disease. This led to the detection of previously unsuspected Trypanosoma cruzi infection in 67.8% of the serum samples in which the EVI antibody was detected after observation of a positive vascular pattern with mouse liver cryostat sections. On the other hand, no significant relationship between Chagas infection and sera with other anti-striated-muscle immunofluorescent patterns that also showed a vascular staining on mouse liver cryostat sections was established. Consideration of the vascular pattern observed with the EVI antibody on mouse liver cryostat sections can be helpful in detection of previously ignored T. cruzi infection in patients who have connective-tissue diseases and related conditions. This is of interest in view of the fact that anergic immunodepressive therapy, often used in these patients, significantly alters the host-parasite relationship and may lead to severe dissemination of the parasite.

The guinea pig model for Argentine hemorrhagic fever.

Guinea pigs infected by the peripheral route with the XJ pathogenic strain of Junin virus showed viscerotropism mainly in reticulo-phagocytic rich organs. By immunofluorescence, heavy infection of reticular-phagocytic cells was demonstrated, supporting the leading role of these cell types. Absence of neurotropism was demonstrated by the inability to recover infectious virus, as well as the absence of antigens, immunoglobulins, or 3rd component of complement deposits, in cells, vessels, or meninges. The correlation between infectivity and antigen expression observed in organs, and the absence of evidence of immunopathologic mechanisms, strongly suggest a direct viral effect in these experimental conditions. The results show that infection of guinea pigs by the peripheral route is an adequate model for human Argentine hemorrhagic fever with the exception of central nervous system involvement. Comparisons are made with infections produced in guinea pigs by attenuated strains, as well as with the disease in primates and humans.

Investigation of the EVI antibody in parasitic diseases other than American trypanosomiasis. An anti-skeletal muscle antibody in leishmaniasis.

The specificity of a circulating antibody observed in American trypanosomiasis and reacting with endocardium, blood vessels, and the interstitium of striated muscle (EVI factor) was evaluated in the indirect fluorescent antibody test with 60 sera from patients with malaria, leishmaniasis, echinococcosis, amebiasis, African trypanosomiasis, toxoplasmosis, and trichinosis, collected from areas where Chagas' disease is not endemic. Two sera, 1 from a patient with Plasmodium falciparum malaria and 1 from a patient with a relapse pretreatment post kala-azar dermal leishmaniasis, were positive for the EVI factor. In the leishmaniasis group, 3 of 8 sera reacted with 0ovine, murine, and human skeletal muscle. In this reaction, which differs from the EVI test, the sarcolemma and the intracellular structures were stained.

Cryostat sections with tissue amastigotes of Trypanosoma cruzi as a substrate for Chagas' disease serology.

Sera from 30 chronic chagasic patients together with 52 control samples (34 with other pathological conditions and 18 from normal individuals) were titrated by the indirect immunofluorescent technique (IFA) on Trypanosoma cruzi amastigotes. Acetone-fixed cryostat sections of skeletal muscle of Rockland mice 10 days post-infection with the RA isolate of T. cruzi were used as substrate. Results were compared with titres obtained by conventional IFA on epimastigotes. All 52 control sera had amastigote titres less than or equal to 2 double dilutions (dd) as compared with epimastigote values. Out of the 30 chagasic samples, differences were greater than or equal to 4 dd (less than or equal to 1 log) for 22, 3 dd for 5 and less than or equal to 2 dd for the remaining 3, when comparing amastigote and epimastigote titres. These results show that the use of amastigotes in cryostat sections of infected tissue for performing Chagas' serology in a simple, adequate and sensitive method.

Lymphatic tissue in Argentine hemorrhagic fever. Pathologic features.

Spleen and lymph nodes from seven fatal cases of Argentine hemorrhagic fever were studied by light and electron microscopy and by immunofluorescent techniques. In addition, Junin virus infectivity was determined. Destruction of splenic white pulp and of lymph node cortex was observed. The ultrastructural study showed a characteristic cytopathic effect on the macrophages with presence of intracisternal virus-like particles and occasional virions budding from the plasma membrane. The immunofluorescent techniques indicated the presence of Junin virus antigenic determinants in the cytoplasm of macrophages in the examined organs. Junin virus titers were three times higher than in peripheral blood. These results suggest that lymphatic tissue is one of the main sites of viral replication and that the macrophages are the targets of Junin virus.

Experimental Chagas disease in a South American primate (Cebus sp).

Two year old Cebus sp monkeys were infected with the Argentine strain of T. cruzi by the conjuctival route employing metacyclic forms of the parasite, obtained from dejecta of T. infectans. Both animals developed parasitemia detected by xenodiagnosis, without any overt acute disease, and with serological conversion. After 9-10 months of infection, both animals developed significant ECG abnormalities. One animal died spontaneously and the other was sacrificed. At necropsy, both animals presented significant megacolon. Severe thinning of the intestinal wall was observed without inflammatory lesions and with preservation of the parasympathetic plexus. Histologic studies revealed fibrotic lesions in the myocardium. In this organ, lymphocytic infiltrates were found in infrequent and small foci, but no pseudocytic forms containing parasities were observed. These observations suggest that the Cebus monkey may be a useful experimental model for some major aspects of chronic Chagas disease in man.