Histamine H1 and H4 receptor expression on the ocular surface of patients with chronic allergic conjunctival diseases

BackgroundThis study investigated the histamine H1 and H4 receptors mRNA (H1R and H4R, respectively) expression on the ocular surface of patients with chronic forms of allergic conjunctival diseases to determine whether they can serve as biomarkers for allergic inflammation in the conjunctiva.MethodsWe examined 19 patients with vernal or atopic keratoconjunctivitis (AKC/VKC group) and 15 healthy volunteers (control group). The AKC/VKC group was divided into active and stable stage subgroups. Specimens were obtained from the upper tarsal conjunctiva of each participant using a modified impression cytology method. H1R, H4R, and eotaxin-1, -2, and -3 mRNA (eotaxin-1, eotaxin-2, eotaxin-3, respectively) expression was determined by real-time RT-PCR. Immunohistochemical analysis for eosinophil cationic protein (ECP), eosinophil major basic protein (MBP), eotaxin-2, and histamine H4 receptor (H4R) were performed using conjunctival smears.ResultsThe number of H4R-positive patients was higher in the active than the stable stage subgroup and control group, whereas no difference was observed for H1R. H1R levels were higher in the active than in the stable stage subgroup, while those of H4R were higher in the active stage subgroup than in the control group. H1R and H4R levels were correlated with eotaxin-2 level. In immunohistochemical analysis, H4R revealed their expression on eosinophils in conjunctival smears of patients with AKC/VKC.ConclusionsH4R is useful as biomarkers of allergic inflammation on ocular surfaces. Most notably, H4R expressed on eosinophils is useful as a biomarker of eosinophilic inflammation of the ocular surface.