Expression of defensin antimicrobial peptides in the peritoneal cavity of patients on peritoneal dialysis

Abstract

◆ Objective: To investigate the expression and regulation of defensins in the peritoneal cavity of peritoneal dialysis (PD) patients. ◆ Design: The presence of defensins in the peritoneal cavity was assessed using reverse transcription polymerase chain reaction (RT-PCR). In vivo defensin expression was analyzed in human peritoneal membrane biopsies and in peritoneal cavity leukocytes isolated from spent dialysate. Defensin expression in vitro was assessed in cultured human peritoneal mesothelial cells (HPMC) and confirmed with PCR Southern blot and DNA sequencing. The effect of tumor necrosis factor alpha (TNFα) and epidermal growth factor (EGF) on β2 defensin expression in HPMC was analyzed by Northern blot analysis and RT-PCR respectively. ◆ Results: Both α and β classes of defensins are expressed in the peritoneal cavity of PD patients. Messenger RNA for the α-defensin human neutrophil peptide 3 and for β-defensin-1 (hβD-1) were found in preparations containing predominantly peritoneal leukocytes, whereas β-defensin-2 (hβD-2) is expressed by HPMC. HPMC isolated from different individuals displayed variability in both basal hβD-2 expression and in response to stimulation by TNFα. Conversely, EGF consistently downregulated the level of hβD-2 message in HPMC. ◆ Conclusion: α- and β-defensins are expressed in the peritoneal cavity, and hβD-2 is the main defensin present in the peritoneal membrane. Variable levels of expression of hβD-2 by mesothelial cells were seen, with evidence of regulation by cytokines and growth factors. This provides evidence for a previously unknown mechanism of innate immunity at that site.