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Viable metacyclic forms of T. cruzi, Y strain, treated with an adequate dose of actinomycin D (50 micrograms Act-D/ml/10(7) parasites/ml for 72 h at 28 degrees C) showed the following properties: 1) they lost their ability to replicate in culture medium, in blood and in tissues of normal mice and were no longer able to incorporate tritiated thymidine; 2) they could not penetrate into Vero cells and could not replicate inside normal macrophages; 3) they retained their immunogenicity and the ability to protect mice against a virulent infection; 4) they did not induce histological lesions as described in chronic experimental Chagas' disease.

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Mice infected with T. cruzi, Y strain, acquire a high level of susceptibility to the effects of bacterial gram-negative LPS. The LD50 of adult female SW mice to LPS from S. typhosa, decreases from 450 to 2,5 mcg 10-12 days after T. cruzi infection. This hyperreactivity to LPS induced by T. cruzi presents all the characteristics of that found in infection caused by many other agents. During the acute phase of experimental infection with T. cruzi Y strain, mice generally die with a hypovolemic shock very similar to that induced in uninfected animals injected with an adequate dose of bacterial endotoxin. There is evidence for and against the hypothesis that LPS absorbed from the intestinal tract may be involved in the mechanism of death of mice during the acute phase of T. cruzi infection.

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Camundongos infectados com a cepa Y do T.cruzi adquirem elevado grau de reatividade ao LPS de S. typhosa. A LD50 de camundongos SW, adultos, femeas, com peso em torno de 20g, decresce de 450 para 2,5 mcg ao fim de 10-12 dias de infeccao.Esta hiperatividade ao LPS induzida pelo T. cruzi apresenta todas as caracteristicas daquela encontrada nas infeccoes causadas por muitos outros agentes. Durante a fase aguda da infeccao experimental com T. cruzi, cepa Y, os camundongos geralmente morrem com choque hipovolemico muito semelhante ao ocasionado por dose adequada de endotoxina bacteriana. Ha evidencias a favor e contra a hipotese de que os LPS liberados do trato intestinal estejam envolvidos no mecanismos de morte do camundongo durante a fase aguda da infeccao pela cepa Y do T.cruzi

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Pesquisas realizadas em camundongos Sw, nao singeneicos, mostraram nao ter havido correlacao entre a intensidade da reacao granulomatosa pulmonar e o grau de resistencia adquirida contra a infeccao por S.mansoni induzida pelo BCG

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Avaliou-se em coelhos e camundongos, a atividade imunogenica e protetora de um extrato antigenico de Schistosoma mansoni, obtido pela estocagem de vermes adultos em solucao salina tamponada (Extrato Salino).A imunizacao dos animais determinuou o desenvolvimento de resposta imune celular e humoral, avaliada por provas especificas.Todos os coelhos imunizados com ES, desenvolveram altos niveis de anticorpo citotoxico (91 a 100%), determinados pela avaliacao de atividade citotoxica in vitro, contra esquistosomulos. Concluiu-se que os coelhos e camundongos imunizados com o extrato salino apresentaram diminuicao da carga parasitaria oriunda da infeccao posterior com cercarias de S. mansoni, em relacao aos controles. Os percentuais de protecao foram de 88.6% e 54% para os animais vacinados (coelhos e camundongos respectivamente)

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Estudos imunologicos foram realizados em 16 pacientes adultos, de ambos os sexos, acometidos de paracoccidioidomicose. Dentre os achados mais importantes figuram os teores elevados de IgG, a baixa do 3o. componente do complemento, a presenca de anticorpos precipitantes e hemaglutinantes contra a paracoccidioidina, a presenca de complexos imunes circulantes, baixos teores de linfocitos T circulantes, teores normais de linfocitos T supressores e hiporreatividade dos linfocitos T a fitohemaglutinina e a paracoccidioidina.A histologia das reacoes cutaneas a paracoccidioidina acusou um aspecto semelhante ao da reacao de Arthus, com o maximo de intensidade do eritema em 24 horas, a presenca de vasculite e a infiltracao predominante por polimorfonucleares

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Studies were carried out with a polyribosomal fraction isolated from Trypanosoma cruzi Y epimastigotes, with the intention to determine both its immunogenic activity and the degree of protection it could induce against experimental T. cruzi infection. This fraction was assayed in four groups of mice by using different schedules of vaccination and varying the dose, intervals, and route of administration. Seven days after the last dose, the animals were sacrificed for immunological studies or subjected to challenge with T. cruzi trypomastigotes. The results obtained in all schedules showed that our polyribosomal fraction only induced a weak antibody response, but was capable of evoking an expressive cellular response. It was also shown that this fraction has the capacity of inducing a high degree of protection against T. cruzi infection, as determined by the decrease of parasitemia and the prolonged survival time of immunized animals.

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