Effects of Trabeculectomy on the Expression of Human Conjunctival Beta–defensins 1 and 2

Abstract

Abstract: : Purpose: Ocular surface epithelia secrete defensins as part of the innate immunity against infection. Human beta defensin–1 (HBD–1) is normally expressed in the conjunctiva whereas human beta defensin–2 (HBD–2) is upregulated in infections. Blebitis is a complication of antimetabolite assisted trabeculectomy. We hypothesized that altered defensin expression in bleb epithelium may predispose or protect this tissue from infection. In this study we compared HBD–1 & HBD–2 expression in the conjunctiva in patients who underwent antimetabolite assisted trabeculectomy and 2 control groups. Methods: Impression cytology was used to collect epithelium a) from the filtering bleb surface & ipsilateral inferior conjunctiva in eyes that were at least 6 months status post trabeculectomy without medications and with absence of previous blebitis (n=12) b) from the superior & inferior bulbar conjunctiva of POAG eyes on medications (n=15) and c) from normal controls (n=14) . Total RNA was extracted from individual samples and HBD–1 & 2 expression analyzed using real time semi quantitative RT PCR. For normalization, 18–s ribosomal RNA was quantitated in parallel and the results analyzed using one way ANOVA. Results: HBD–1 & 2 expression was detected in all conjunctival samples. In normal and POAG eyes, HBD–1 expression was variable but higher (2–5 fold) in the inferior conjunctiva. However, in the trabeculectomy eyes a moderate increase in HBD–1 expression (11 fold) in epithelium over the bleb was noted when compared to the inferior conjunctiva. In general, HBD–2 was expressed at lower levels than HBD–1. As with HBD–1 there was moderately higher HBD –2 expression in the inferior conjunctiva (8–9 fold) in normal and POAG eyes. Similar to HBD–1, increased HBD–2 expression was seen in the filtering bleb surface epithelium when compared to the inferior conjunctiva (3 fold). ANOVA failed to detect differences between HBD–1 or 2 expression between the 3 groups in either superior or inferior conjunctiva. Conclusions: This study confirms variable expression of HBD–1 & 2 in the conjunctiva. It also highlights regional differences in expression of both peptides with increased levels in the inferior conjunctiva in controls and POAG eyes. It is possible that proinflammatory cytokines in the inferior tear meniscus may stimulate the increased defensin expression in the inferior bulbar conjunctiva. The upregulation of HBD–1 & 2 in the bleb area suggests that these antimicrobial peptides may play a role in tissue defense against infections.

Keywords: conjunctiva • inflammation • gene/expression