Publication Date

8-1-1996

Degree Program

Department of Biology

Degree Type

Master of Science

Abstract

Trypanosoma cruzi is an obligate intracellular parasite infecting 18-20 million people in Latin America. It is the causative agent of Chagas' disease, commonly referred to as American Trypanosomiasis. The C3H murine model is widely used to study experimental Chagas' disease. It is well documented that when these highly susceptible mice are infected with the Brazil strain of T. cruzi and maintained at room temperature (RT), mice die between day 35-45 of infection. However, when held at an elevated temperature of 36°C, C3H mice survive an otherwise lethal infection with T. cruzi. When held at 36°C, the body temperature of the mice increases 3-4°C and the mice experience decreased parasitemia and enhanced parasite-specific and non-specific immune responses. The present study was designed to determine whether heat shock proteins (hsps) of the parasite might be playing a role in this phenomenon. In the first set of experiments antibody responses to parasite hsps were analyzed using metabolic labelling with S methionine/cysteine followed by immunoprecipitation, SDS-PAGE and autoradiography. The results showed that by day 15, serum from RT-infected mice recognized proteins of approximately 93kDa, 83kDa, and 66kDa, while in mice held at 36°C the major proteins recognized were 93kDa and 83kDa. By day 25, a high MW band of approximately 183kDa was recognized by serum from mice held at RT and 36°C. A stronger response to the 93kDa, 83kDa, and 66kDa proteins was seen in RT-infected mice as compared to 36°Cinfected mice. By day 35, another high MW protein of approximately 192kDa was recognized by sera from both RT and 36°C-infected mice. Strong reactivity with the 183kDa, 93kDa, 83kDa, and 66kDa proteins was seen in both groups of mice on day 35. By day 45 of infection, serum from 36°C-infected mice recognized proteins of approximately 183kDa, 93kDa, 83kDa, and 66kDa more intensely than in the RT-infected mice group. In addition, a low MW protein of approximately 27kDa was recognized only by serum from 36°C-infected mice. These results provide evidence that parasite heat shock proteins are playing an important role in providing a temperature-related resistance in T. cruzz-infection. In the second set of experiments histopathological changes in the heart and skeletal tissues of mice maintained at RT or an elevated temperature of 36°C were compared. Parasitemias were also performed at regular intervals. Results showed that mice maintained at RT experienced parasitemias as early as day 15 post-infection (p.i.) and the parasite numbers continued to increase until day 42 p.i., at which time the final two RTinfected mice were killed. The infection appeared early in the heart and by day 42 p.i. heavy infiltration of chronic inflammatory cells, severe necrosis, edema, and large numbers of pseudocysts, containing amastigote stages of the parasite, were observed. Skeletal muscle was involved later in infection and displayed similar characteristics as seen in the heart. In contrast, in mice maintained at 36°C parasites were first observed, in blood, on day 21 p.i. Heart and skeletal tissue of mice killed on days 15 and 25 p.i. did not display any observable pathological abnormalities. However, a few pseudocysts were detected in the hearts of mice killed on day 35 p.i. Sections of heart taken from mouse #7 and #8, killed on day 95 p.i. showed some interesting characteristics. Mouse #7 experienced peak parasitemia on day 47 p.i. which was completely resolved by day 76 p.i. In contrast, mouse #8 continued to experience a moderately high parasitemia throughout the course of infection. The histology of the heart and skeletal tissue of mouse #8 revealed some pseudocysts, and infiltration by chronic inflammatory cells. No abnormal changes were observed in the heart and skeletal tissue of mouse #7. The data from this study provide strong evidence that elevated environmental temperature has a negative effect not only on circulating parasites but also on tissue stages of the parasite in both acute and chronic stages of T. cruzi infection in mice held at 36°C.

Disciplines

Medical Sciences

Download

Share

COinS