Background and objectives. Heat shock protein 70 (HSP70) is a highly conserved stress-responsive protein that plays an important role in the survival and adaptation of Leishmania parasites under adverse environmental conditions. Thermal stress is one of the key challenges encountered by Leishmania donovani. This study aimed to evaluate the effect of elevated temperature on HSP70 gene expression and parasite viability under thermal stress conditions. Materials and methods. Promastigotes of L. donovani were cultivated and exposed to different temperatures (37, 40, and 42°C) for defined periods, while parasites cultivated at 26°C were considered the control group. Total RNA was extracted, and HSP70 gene expression levels were assessed using qRT-PCR. Leishmania viability was determined using the MTT assay. Statistical analyses were used to determine differences in gene expression among temperature treatments and to assess correlations between gene expression and viability. Results. HSP70 gene expression was noticeably upregulated in Leishmania parasites exposed to elevated temperatures compared with the control group. The highest expression level was observed at 37°C, with moderate reductions at 40°C and 42°C; however, HSP70 expression remained higher than in the control group. No statistically significant correlation was observed between HSP70 gene expression and L. donovani viability among the different temperature treatments in this exploratory analysis. Conclusions. The findings of this study indicate that HSP70 gene expression in L. donovani is regulated by thermal stress rather than parasite viability. The upregulation of HSP70 under elevated temperatures underscores its role in the thermal stress response and highlights its potential importance in parasite adaptation under different conditions.
