Expression of prostaglandin E2 receptor subtypes in human pterygium and normal conjunctiva: immunohistochemical study

Purpose In the present study, we aimed to evaluate the expression of EP receptors in primary and recurrent human pterygium tissues. Methods Pterygium samples were collected from 65 patients with primary pterygium and 16 patients with recurrent pterygium. Normal conjunctival tissues were collected from nasal interpalpebral area from 17 patients without systemic and any other ocular pathology. Expression of EP receptors was evaluated by immunohistochemistry. The median value for each receptor staining score (RSS) was determined in normal conjunctival specimens. In this study, RSS of > median value was defined as positive staining or high expression and <= median value as negative staining or weak expression in specimens. Chi-square test was used for statistical analysis, and p value of less than 0.05 was considered significant. Results Stromal expression of EP1 was significantly higher in primary and recurrent pterygium specimens compared to normal conjunctival tissues (p = 0.007 and p = 0.002, respectively). Epithelial expressions of EP2 and EP3 were significantly lower in primary pterygium specimens compared to normal conjunctival tissues (p = 0.005 and p < 0.0001, respectively), and stromal expressions were insignificant. Stromal expression of EP4 was significantly higher in primary and recurrent pterygium specimens compared to normal conjunctival tissues (p = 0.002 and p = 0.012, respectively). Conclusions Expression of EP receptors has been up- or downregulated in primary and recurrent pterygium tissues, and these receptors may play a role in formation and recurrence of pterygium.