Exacerbation of Experimental Trypanosoma cruzi Infection in Mice by Concomitant Malaria*

SYNOPSIS. The effect of malaria on the chronic phase of Chagas’disease was investigated in mice. The animals were given Plasmodium berghei-infected red blood cells 2 to 12 months after their initial inoculation with trypomastigotes of 3 different strains of Trypanosoma cruzi (Y, CL and Gilmar). In all the experiments carried out with one of the strains (CL), a somewhat variable but always considerable percentage of mice (average 39%) relapsed in to the acute phase of Chagas’disease. This relapse was characterized by a significant increase in the number of circulating trypomastigotes. Recrudescence was observed also with a 2nd strain of T. cruzi (Gilmar), which is similar in many aspects to the CL strain, e.g. the morphology of blood stages, curve of parasitemia and susceptibility to antibodies in vitro. In mice whose chronic phase was induced by trypomastigotes of the Y strain, malaria infections did not induce a typical acute phase with high parasitemia by T. cruzi. Bloodstream forms of Y parasites differ from those of CL and Gilmar strains morphologically as well as immunologically, i.e. only the Y strain is easily agglutinated and partly inactivated by specific immune serum. In light of this and other known characteristics of the strains used in the present work, the author speculates on mechanisms which allow malaria infections selectively to suppress acquired host resistance to certain strains of T. cruzi.     

Comparative Kinetics of Arginine and Lysine Transport by Epimastigotes and Trypomastigotes from Two Strains of Trypanosoma cruzi*

SYNOPSIS. Three-day-old cultures of Y and MR strains of Trypanosoma cruzi had a higher rate of lysine and arginine uptake than 10-day cultures. Amino acid uptake by cells of the MR strain was consistently higher than that of the Y strain. Flagellates separated on DEAE-cellulose columns have normal structure, motility, and infectivity; they have higher rates of lysine and arginine uptake than the original 3- and 10-day cultures. In addition, passage through DEAE-cellulose columns modified the kinetic behavior of amino acid transport systems in the flagellate membranes. Methionine inhibited uncompetitively uptake of lysine and arginine by MR and Y strains. Lysine inhibited arginine uptake by both strains by an uncompetitive mechanism. Lysine, however, inhibited the uptake of arginine by 10-day culture cells of the Y strain by a mixed-type of inhibition. Arginine also inhibited the lysine uptake of both strains by an uncompetitive mechanism. In all experiments, beyond a certain level, a further increase in inhibitor concentration resulted in a decreased inhibition, which eventually disappeared altogether. Inhibition of amino-acid uptake by any of the substances tested was not observed after passage of flagellates through a DEAE-cellulose column. A model for amino acid transport was formulated which includes a recognition site amenable to modulation by effectors.     

The Effects of Bacterial Endotoxin on the Infection of Mice with Trypanosoma cruzi*

Mice (Rockland strain) infected with Trypanosoma cruzi strain Tulahuén were treated with Escherichia coli endotoxin before, simultaneously with, and after inoculation of the parasites. The peak parasitemias of endotoxin-treated mice were higher than those of nontreated infected animals, regardless of the time of endotoxin administration. Peak parasitemias occurred at the same time in infected nontreated mice as in animals given endotoxin before or simultaneously with the trypanosomes. If endotoxin was administered 24 hr after the infection, a delay in the peak parasitemia was noted. Changes in the survival time were not observed unless endotoxin was given 24 hr postinfection. Infected mice had an increasing susceptibility to the lethal effect of endotoxin. The LD₅₀ of endotoxin decreased from 675 μg for normal mice to 230, 92, and 18 μg for infected animals 1, 3, and 8 days after the infection, respectively. In the infected mice, the endotoxin-detoxifying ability of the spleen was found to be impaired.     

Trypanosoma cruzi: Correlation of Growth Kinetics to Zymodeme Type in Clones Derived from Various Sources*†

SYNOPSIS. Trypanosoma ( Schizotrypanum ) cruzi clones were derived from isolates of an acute human case of Chagas' disease (strain Esmereldo), a human case of T. cruzi infection (strain CAN-III) and from a naturally infected opossum (strain WA-250). The isoenzyme patterns and growth rates of the clones were stable during long-term cultivation, by serial passages, of the parasites in liquid medium. Both clones of strain Esmereldo were zymodeme II; the 2 clones of strain CAN-III, zymodeme III; and the 5 clones of strain WA-250, zymodeme I. The range in doubling times of the parasite populations in liquid medium were 36–49. 7 h (strain WA-250), 117.2–133.7 h (Esmereldo clones) and 169–208 h (CAN-III clones).     

Electron Microscopic Study of Trypanosoma cruzi Periplast in Tissue Cultures. I. Number and Arrangement of the Peripheral Microtubules in the Various Forms of the Parasite's Life Cycle*

SYNOPSIS. In an electron microscopic study, counts of peripheral microtubules were made in spheromastigotes and trypomastigotes in tissue cultures of embryonic heart muscle cells. In interphase spheromastigotes there were, at the level of the nucleus, ～ 114 microtubules; in dividing forms, there were ～ 222. In trypomastigotes, the number of microtubules varied according to the level of the section—there were fewer than 40 tubules in the pointed ends of an organism, while in the central segment the number of these elements ranged from 60 to 115. The highest number of microtubules was found in the region containing the Golgi complex. The distance between the microtubules was constant, equalling 44 nm, even at the pointed ends of a trypanosome. This suggests that the microtubules course parallel to one another. Cross sections and randomly arranged, variable length, longitudinal sections of the tubules were noted around the kinetosomes in dividing organisms.     

On the Fine Structure of Trypanosoma cruzi in Tissue Cultures of Pigment Epithelium from the Chick Embryo. Uptake of Melanin Granules by the Parasite*

Trypanosoma cruzi has been cultured in pigment epithelial cells of the iris from the chick embryo. Melanin granules, identical with those of the host cells were found in the intracellular, amastigote (leishmania) forms. In many of the intracellular forms cytostome-like structures were seen, often in intimate contact with the pigment granules of the host cells, which suggests the uptake of melanin granules through the cytostomes by the process of intracellular phagotrophy.     

[3H]8-Hydroxy-2-(Di-n-Propylamino)Tetralin Binding to Pre- and Postsynaptic 5-Hydroxytryptamine Sites in Various Regions of the Rat Brain

The specific binding of [3H]8-hydroxy-2-(di-n-propylamino)tetralin ([ 3H]8-OH-DPAT) to 5-hydroxytryptamine (5-HT)-related sites was investigated in several regions of the rat brain. Marked differences were observed in the characteristics of binding to membranes from hippocampus, striatum, and cerebral cortex. Hippocampal sites exhibited the highest affinity (KD approximately 2 nM) followed by the cerebral cortex (KD approximately 6 nM) and the striatum (KD approximately 10 nM). Ascorbic acid inhibited specific [3H]8-OH-DPAT binding in all three regions but millimolar concentrations of Ca2+, Mg2+, and Mn2+ enhanced specific binding to hippocampal membranes, whereas only Mn2+ increased it in the cerebral cortex and all three cations inhibited specific binding to striatal membranes. Guanine nucleotides (0.1 mM GDP, GTP) inhibited binding to hippocampal and cortical membranes only. As intracerebral 5,7-dihydroxytryptamine markedly decreased [3H]8-OH-DPAT binding sites in the striatum, but not in the hippocampus, the striatal sites appear to be on serotoninergic afferent fibers. In contrast, in the hippocampus the sites appear to be on postsynaptic 5-HT target cells, as local injection of kainic acid decreased their density. Both types of sites appear to be present in the cerebral cortex. The postsynaptic hippocampal [3H]8-OH-DPAT binding sites are probably identical to the 5-HT1A subsites, but the relationship between the presynaptic binding sites and the presynaptic autoreceptors controlling 5-HT release deserves further investigation.