Aim: The aim was to study the expression of Secretory Leukocyte Protease Inhibitor (SLPI) and to explore its correlation with the presence of Epstein-Barr Virus (EBV) among patients with nasopharyngeal carcinoma.
Materials and methods: The expression levels of SLPI mRNA in NPC cell lines and in ten matched-pairs of NPC and adjacent normal tissue were examined by quantitative real-time Polymerase Chain Reaction (PCR). Furthermore, protein expression of SLPI in 71 paraffin-embedded NPC biopsies was assessed by immunohistochemistry. Finally, the serum level of SLPI in 177 NPC patients and 103 healthy controls was evaluated by enzyme-linked immunosorbent assay (ELISA).
Results: The expression of SLPI mRNA in NPC cells was significantly lower than in the adjacent normal epithelium (p<0.001). When the expression of SLPI in EBV-positive and -negative NPC cell lines was compared, we found that both mRNA and protein expressions of SLPI were significantly higher in EBV-negative cells. Furthermore, the results of immunohistochemical analysis demonstrated that the frequency of reduced SLPI expression in EBV-positive biopsies was significantly higher than that in EBV-negative biopsies.
Conclusion: In this study, we have confirmed that SLPI is significantly down-regulated in NPC tissues. In addition, based on our preliminary results, we propose that the reduction of SLPI in NPC cells is associated with the presence of the EBV genome and/or the expression of EBV-encoded genes. SLPI may play an important role in EBV-mediated NPC tumorigenesis.