[Cytochemical study of nucleic acids in relation to the polymorphism of the trypomastigote forms of Trypanosoma cruzi].

Four morphological types of T. cruzi trypomastigotes are distinguished in mouse blood. These differ in RNA contents, in the distribution pattern of RNA in the cytoplasm, in the intensity of the Feulgen reaction and the topography of DNA in the nucleus, and in the contents and distribution of both the nucleic acids in the kinetoplast. Among the trypomastigotes examined, forms C and S differ at a lesser degree, than their slender and middle variants differing much stronger. The early slender trypomastigotes are characterized by poor and diffuse RNA in the cytoplasm, by a homogeneous distribution of DNA in the nucleus and by a low content of DNA (sometimes RNA) in the kinetoplast. The middle trypomastigotes, dominating at the final step of the infection, are rich in granular RNA, differ (despite their inability to divide) in their nuclear organization mostly characterized by a large karyosome and uneven distribution of chromatin at the periphery; the kinetoplast is rich in DNA and often contains RNA. The peak of trypomastigotes with the kinetoplast deprived of obviously stained RNA precedes the impetuous increase of parasitemia. It coincides with the decrease in the number of destroyed parasites, and with the active substitution of slender variants by the middle ones within both C- and S-forms. Thus, changes in the nucleus and kinetoplast are involved in the trypomastigote transformation and in the development of infection.