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C. De Dominicis, P. Brun, L. Motterle, M. Bortolotti, F. Piliego, A. Leonardi; Histamine H1R, H2R, H3R and H4R Receptors in Normal Conjunctiva and in Vernal Keratoconjunctivitis. Invest. Ophthalmol. Vis. Sci. 2008;49(13):418.
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© ARVO (1962-2015); The Authors (2016-present)
Histamine is the main mediator of the allergic response, however the presence and distribution of histamine receptors (HR) are not well documented in the human eye. The aim of this study was to evaluate HR expression in conjunctival tissues from normal subjects and from chronically inflamed, vernal keratoconjunctivitis (VKC) patients.
Mucosal biopsies were obtained from conjunctiva of healthy donors (N=9) and from tarsal conjunctiva of VKC patients (N=9). Immunostaining for H1R, H2R, H3R and H4R, eosinophils (EG2), mast cells (tryptase), and lymphocytes (CD4) and vascular endothelial cells (CD31) was evaluated. Double immunostaining for H1R /CD31 and for H4R/EG2 and H4R/CD4 was also performed in pathological tissues.
Immunostaining for H1R was faintly present in normal conjunctiva and over-expressed in all VKC samples. H1R was particularly expressed by vascular endothelial cells. H2R was slightly evident in normal tissues and over-expressed in VKC. As expected, the H3R was rarely found in normal or inflamed conjunctiva. H4R was highly expressed in all VKC tissues, particularly by stromal inflammatory cells. In pathological tissues, double staining demonstrated the H4R in both eosinophils and CD4+ cells.
H1R, and H2R, are normally expressed in human conjunctiva. The findings of increased expression of H1R, H2R, and H4R in VKC conjunctival tissue and the expression of H4R by inflammatory cells indicate a potentially important role of the H4R in the pathogenesis of allergic disorders. Modifying the H4R may be a future target in the treatment of allergic inflammation.
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