Histamine H4 receptors in normal conjunctiva and in vernal keratoconjunctivitis.

BACKGROUND: While it is known that histamine is the primary mediator of ocular allergy, the presence and distribution of histamine receptors are not well documented in the human eye. Our aim was to evaluate histamine receptor expression in normal and vernal keratoconjunctivitis conjunctiva. METHODS: Mucosal biopsies were obtained from conjunctiva of healthy donors and from tarsal conjunctiva of vernal patients. Immunostaining and semi-quantitative reverse-transcriptase polymerase chain reaction for H(1), H(2), H(3), and H(4) receptors were performed. Histamine receptor expression was also evaluated in conjunctival cell cultures exposed to histamine, interleukin-4, interleukin-5, interferon-γ and tumor necrosis factor-α. RESULTS: Immunostaining for H(1) and H(2) receptors was slightly positive in normal and over-expressed in vernal tissues. H(3) receptors were rarely present in normal and inflamed conjunctiva. In striking contrast to control tissues, H(4) receptors were highly expressed in all inflamed tissues, particularly by stromal inflammatory cells. Semi-quantitative reverse-transcriptase polymerase chain reaction demonstrated an over-expression of H(1), H(2), and H(4) receptors in vernal vs control tissues. Notably, H(4) receptors were five times more expressed in vernal vs control tissues. In cell cultures, H(2) receptor expression was stimulated eight times the normal levels by interleukin-4 and three times by histamine, but the H(4) receptor was only slightly affected by stimulation with these mediators. CONCLUSIONS: Increased expression of H1, and particularly of H(2) and H(4) receptors in vernal keratoconjunctival tissues indicate their important role in the pathogenesis of this disease. H(4) receptors may be a target in the treatment of allergic inflammation.

Transforming growth factor-ß/Smad - signalling pathway and conjunctival remodelling in vernal keratoconjunctivitis.

BACKGROUND: Vernal keratoconjunctivitis (VKC) is a chronic ocular allergic inflammation characterized by corneal complications and the formation of giant papillae. Sma- and Mad-related proteins (Smad) modulate extracellular matrix gene expression during wound healing, inflammation and tissue remodelling. OBJECTIVE: To investigate the relationship between allergic inflammation and TGF-ß/Smad signalling pathway, expression in VKC patients and in primary cultured conjunctival fibroblasts exposed to mediators found previously over-expressed in VKC. METHODS: Smad-2, -3, -7, phospho-(p)Smads, TGF-ß1 and -ß2 were evaluated in the conjunctiva of normal subjects (CT) and VKC patients by immunohistochemistry. The expression of Smads, pro-collagen I (PIP), TGF-ß1, -ß2, mitogen-activated protein kinase (p38/MAPK), c-Jun N-terminal kinase (JNK) and extracellular signal-regulated kinase (ERK1/2) were also determined in conjunctival fibroblast cultures exposed to histamine, IL-4, -13, TGF-ß1, IFN-γ and TNF-α using immunostaining or RT-PCR. RESULTS: Immunostaining for Smad-2, -3, pSmad-2, -3, TGF-ß1, -ß2 and PIP was significantly increased in VKC stroma compared with CT. In conjunctival fibroblast cultures, Smad-3 and PIP were stimulated by histamine, IL-4, -13 and TGF-ß1 exposure, while PIP was reduced by IFN-γ, and TNF-α mRNA expression of Smad-3 was increased by histamine, while Smad-7 was reduced by IL-4. In addition, histamine, IL-4 and TNF-α increased JNK and ERK1/2 expression. CONCLUSION AND CLINICAL RELEVANCE: The TGF-ß/Smad signalling pathway is over-expressed in VKC tissues and modulated in conjunctival fibroblasts by histamine, IL-4, TGF-ß1 and TNF-α. These mechanisms may be involved in fibrillar collagen production, giant papillae formation and tissue remodelling typical of VKC and might provide new therapeutic targets for its treatment.

Allergy and the eye.

The eye represents an ideal and frequent site for the allergic reactions. The term 'allergic conjunctivitis' refers to a collection of disorders that affect the lid, conjunctiva and/or cornea. Even though the diagnosis is essentially clinical, local tests such as cytology, conjunctival provocation and tear mediator analysis can be performed. The immunoglobulin E (IgE)-mediated mechanism does not explain completely the severity and the clinical course of chronic allergic ocular diseases such as vernal (VKC) and atopic keratoconjunctivitis (AKC), which are probably also related to T cell-mediated responses, massive eosinophil attraction and activation and non-specific hypersensitivity. An altered balance between T helper type 1 (Th1) and Th2 cells and between Th1- and Th2-types of cytokines is thought to be responsible of the development of ocular allergic disorders. New findings suggest that a wide range of cytokines, chemokines, proteases and growth factors are involved by complex interwoven interactions rather than distinct and parallel pathways. In addition, several non-specific enzymatic systems may be activated during acute and chronic allergic inflammation, thus contributing to the complex pathogenesis of the disease. Current drug treatment for ocular allergy targets the key mechanisms involved in the development of clinical disease: mast cells with mast cell stabilizers, histamine with histamine receptor antagonists and inflammation with corticosteroids, severe inflammation with immunomodulators. None of these agents lacks side effects and none abolishes signs and symptoms completely. New therapeutic strategies are still needed to respond to the complex pathogenesis of severe forms of ocular allergy such as VKC and AKC.

Matrix metalloproteases in vernal keratoconjunctivitis, nasal polyps and allergic asthma.

BACKGROUND: Allergic conditions in different organs share many similarities in their inflammatory response. Vernal keratoconjunctivitis (VKC), asthma and nasal polyps exhibit several similar, but site-specific mucosal structural changes. The aim of the study was to investigate whether matrix metalloproteases contribute to different tissue remodelling aspects in different organs. METHODS: Mucosal biopsies were obtained from conjunctiva of healthy donors, tarsal conjunctiva of vernal patients, bronchi of non-asthmatic subjects, bronchi of mild stable asthmatic patients, nasal mucosa of non-allergic donors and nasal polyps of allergic patients. Distribution of metalloprotease-1, -3, -9, -13, tissue inhibitor of metalloproteases-1, collagens I and III and the presence of eosinophils and CD4+ cells were evaluated by immunohistochemistry. RESULTS: Collagens were highly diffuse in the giant papillae of VKC and in nasal polyps, and yet less increased in the subepithelium of asthmatic patients. Immunostaining for metalloprotease-1, -3, -9 and -13 was significantly higher in VKC compared with normal conjunctiva. Metalloprotease-9 staining was higher in the stroma of polyps vs. normal nasal mucosa, and only metalloprotease-13 was significantly more expressed in asthmatic vs. non-asthmatic subjects. Metalloprotease-9 immunostaining was more intense in vernal compared with other tissues. In all pathological tissues, metalloprotease-9-positive staining was in association with eosinophils and CD4+ cells. CONCLUSIONS: Expression of metalloproteases may play an important role in inducing the structural changes seen in VKC, nasal polyps and asthma. Tissue remodelling and gelatinase immunoexpression was more dramatic in giant papillae of vernal patients compared with other tissue sites of chronic allergic inflammation.