Trypanosoma cruzi: reversal of inhibition of host muscle differentiation after exposure to elevated temperatures.

The L6E9 myoblast cell line can be grown as individual cells in "growth medium," or can be induced to fuse and differentiate to form multinucleated myotubes either at 37 C or at 40.5 C in "differentiation medium." It has previously been shown that myoblasts with infected Trypanosoma cruzi (Brazil strain) cannot differentiate to form myotubes. Moreover, the mRNAs for contractile proteins are not induced in these infected cells. Infected myoblasts grown in "differentiation medium" at 37C were unable to differentiate by 7 days. The infection was maintained at 100%, and the number of trypomastigotes in the supernatant increased with time (peak greater than 10(6)/ml). At 40.5C, however, infected myoblasts gradually eliminated their infection. The percentage of parasitized cells was reduced to less than 1% by the 7th day of observation. There was also a decrease in the number of trypomastigotes in the supernatant. Moreover, significant fusion was observed in these cultures by morphological criteria. Using 32P-labeled recombinant DNA probes, it was shown that, at 37C, there was an inhibition of mRNAs for muscle-specific contractile proteins (myosin heavy chain and alpha-actin), whereas nonspecific mRNAs were not inhibited. Furthermore, infected myoblasts exposed to 40.5C exhibited no inhibition of mRNAs for myosin heavy chain and alpha-actin. Myoblasts cleared of their infection could readily be reinfected. This study demonstrates that the inhibition of muscle differentiation induced by T. cruzi is reversible when cultures are exposed to elevated temperatures.

Alteration of the pattern of beta-adrenergic desensitization in cultured L6E9 muscle cells infected with Trypanosoma cruzi.

L6E9 myoblasts infected with Trypanosoma cruzi undergo desensitization to beta-adrenergic catecholamines in a manner distinct from uninfected control myoblasts. Following incubation of intact cells with isoproterenol for 2 h, homogenates prepared from differentiated, high density uninfected L6E9 cells retain isoproterenol-dependent adenylate cyclase activity. In addition, previous exposure to isoproterenol is accompanied by a decrease in the number of beta-adrenergic receptors. Homogenates of high density L6E9 cells infected with T. cruzi retain their adenylate cyclase responsivity to isoproterenol but demonstrate a marked decrease in beta-adrenergic receptors. Following desensitization infected cell homogenates lose their responsiveness to isoproterenol and demonstrate a more marked decrease in beta-receptors. There does not appear to be any effect of T. cruzi infection on affinity of beta-adrenergic agonists for the beta-receptor or on changes in agonist affinity associated with desensitization. Infection of low density undifferentiated cells results in no apparent change in adenylate cyclase activity or in beta-receptors. Their behavior in the setting of desensitization--decreased whole cell cyclic AMP, decreased adenylate cyclase, unchanged beta-receptors--is also not affected by infection. The pattern of desensitization to beta-adrenergic agonists in high density infected cells shares several properties with the pattern of desensitization in low density uninfected cells, suggesting that infection may be associated with part of the more primitive cellular response pattern.

Babesiosis in asplenic hosts.

A case of babesiosis in an asplenic individual is reported. A course characterized by fever, haemolysis, hepatitis, depressed mental status and non-cardiac pulmonary oedema was observed. Studies performed on the patient's lymphocytes revealed profound depression in mitogenic responses during her acute disease which returned to normal with recovery. Serum factor(s) were implicated in causing these changes. Review of the literature on babesiosis in asplenic hosts revealed European patients with disease caused by bovine species of Babesia are at significantly higher risk of a fatal outcome than North Americans with disease caused by murine species.

Inhibition of muscle differentiation by trypanosoma cruzi.

L6E9 rat myoblasts were infected in tissue culture with the myotropic Brazil strain of Trypanosoma cruzi. The effect of parasite infection on the ability of myoblasts to differentiate into myotubes was studied. Both morphological and biochemical differentiation were found to be profoundly affected by parasitic infection in a dose-related fashion. Evidence is presented to suggest that infected myoblasts can no longer differentiate. Differentiation, once underway, seemed unaffected by the parasitic infection; biochemical markers of differentiation remained intact.

Successful chemotherapy of transfusion babesiosis.

We describe babesiosis transmitted by transfusion. The infected blood donor was identified and a minimum period of infectivity of the donor's blood was established. We report a new modality for chemotherapy consisting of quinine plus clindamycin, and a new endemic focus for this zoonosis on Fire Island, New York. There are insufficient data to establish a reasonably safe period after which visitors and residents of Babesia-endemic foci can become blood donors. Screening of such persons by a rapid serologic test, such as the ELISA or immunofluorescent antibody tests, is suggested.