Tehran University of Medical Sciences Iranian Journal of Microbiology 2008-3289 18 2 2026 04 26 217 225 Rozalin Mardani Cellular and Molecular Research Center, Yasuj University of Medical Sciences, Yasuj, Iran Majid Borhaniasl Cellular and Molecular Research Center, Yasuj University of Medical Sciences, Yasuj, Iran Mohammad Amin Ghatee Cellular and Molecular Research Center, Yasuj University of Medical Sciences, Yasuj, Iran; Professor Alborzi Clinical Microbiology Research Center, Shiraz University of Medical Sciences, Shiraz, Iran Seyed Abdolmajid Khosravani Cellular and Molecular Research Center, Yasuj University of Medical Sciences, Yasuj, Iran Kasra Sharifi Student Research Committee, Medical College, Islamic Azad University, Kazeroon Branch, Kazeroon, Iran Khodakaram Jahanbin Department of Pathology, Legal Medicine Research Center, Legal Medicine Organization, Yasuj, Iran Asghar Sharifi Cellular and Molecular Research Center, Yasuj University of Medical Sciences, Yasuj, Iran 2024 10 27 2026 02 01 Background and Objectives: Salmonella enterica survival depends on evading CD8+ T-cell recognition, a process governed by the MHC Class I antigen presentation pathway. The cytosolic aminopeptidases—bleomycin hydrolase (BH), puromycin-sensitive aminopeptidase (PSA), and thimet oligopeptidase (TOP)—are critical "final trimmers" that generate the precise peptide epitopes required for MHC Class I loading. This study investigated whether S. enterica cell extract modulates the transcriptional expression of these key enzymes in HT-29 cells, potentially revealing a mechanism of immune evasion mediated by bacterial structural components. Materials and Methods: Human colorectal adenocarcinoma HT-29 cells were treated with varying concentrations of S. enterica extract. The gene expression levels of BH, PSA, and TOP were quantified using qRT-PCR at multiple time points (6, 12, 24, 48, and 72 hours) post-treatment. Data were statistically analyzed to evaluate significant modulations relative to untreated controls. Results: The transcriptional response to S. enterica extract was highly selective, with TOP demonstrating the most robust and rapid induction. Significant upregulation of TOP occurred as early as 6 hours post-treatment and reached its maximum induction at 48 hours. Conversely, BH levels remained largely indistinguishable from untreated controls. PSA expression showed no statistically significant alterations relative to the control group throughout the study. These findings suggest that S. enterica components preferentially target the "terminator" peptidase TOP to potentially disrupt the MHC Class I antigen presentation pathway. Conclusion: S. enterica cell extract significantly and selectively alters the expression of TOP, a critical cytosolic peptidase involved in the final stages of antigen processing. This targeted modulation likely serves as a mechanism for immune evasion by facilitating the destruction of immunogenic epitopes, thereby rendering infected cells less visible to the adaptive immune system. https://ijm.tums.ac.ir/index.php/ijm/article/view/5103 https://ijm.tums.ac.ir/index.php/ijm/article/download/5103/1879