Histamine and tryptase levels in allergic conjunctivitis and vernal keratoconjunctivitis

Understanding Vernal Keratoconjunctivitis: Beyond Allergic Mechanisms

Vernal keratoconjunctivitis (VKC) is a chronic, recurrent, inflammatory disease of the cornea and conjunctiva mostly affecting boys in prepubertal age. VKC recurrence is characterized by intense symptoms of itching, redness, and photophobia associated with corneal damage, impairment of visual function, and quality of life. The pathogenesis of VKC has not yet been completely understood, and it is still controversial. In fact, VKC is considered an ocular allergic disease due to the involvement of immunoglobulin E, eosinophils, and mast cells, and of a lymphocyte T-helper type 2 reaction. However, approximately half of VKC patients have negative allergological history and testing, suggesting that other pathogenic mechanisms participate in VKC development and severity. Specifically, evidence suggests that genetic, endocrine, neuronal factors and an imbalance of innate immunity are involved in the pathogenesis of VKC. The purpose of this review is to summarize evidence on the pathogenic role of innate immunity, neuroimmune reaction, and hormonal changes in VKC. Increasing understanding of the pathogenic mechanisms behind VKC may lead to the identification of novel biomarkers for diagnosis and/or potential therapeutic targets in order to improve the management of this challenging condition.

Lipoxin A4 Counter-regulates Histamine-stimulated Glycoconjugate Secretion in Conjunctival Goblet Cells

Conjunctival goblet cells synthesize and secrete mucins which play an important role in protecting the ocular surface. Pro-resolution mediators, such as lipoxin A₄ (LXA₄), are produced during inflammation returning the tissue to homeostasis and are also produced in non-inflamed tissues. The purpose of this study was to determine the actions of LXA₄ on cultured human conjunctival goblet cell mucin secretion and increase in intracellular [Ca²⁺] ([Ca²⁺]_i) and on histamine-stimulated responses. LXA₄ increased mucin secretion and [Ca²⁺]_i, and activated ERK1/2 in human goblet cells. Addition of LXA₄ before resolvin D1 (RvD1) decreased RvD1 responses though RvD1 did not block LXA₄ responses. LXA₄ inhibited histamine-stimulated increases in mucin secretion, [Ca²⁺]_i, and ERK1/2 activation through activation of β-adrenergic receptor kinase 1. We conclude that conjunctival goblet cells respond to LXA₄ through the ALX/FPR2 receptor to maintain homeostasis of the ocular surface and regulate histamine responses and could provide a new therapeutic approach for allergic conjunctivitis and dry eye diseases.

Mast Cell Chymase Decreases the Barrier Function and Inhibits the Migration of Corneal Epithelial Cells

PURPOSE

We investigated the in vitro effects of human mast cell chymase on corneal epithelial cells.

METHODS

Human corneal epithelial cells were incubated with human chymase at activity levels that were likely to exist in the tears of patients with vernal keratoconjunctivitis.

RESULTS

Incubation of chymase resulted in a decrease of barrier function of corneal epithelium. Occludin protein was cleaved by chymase. In the wound assay, incubation with chymase resulted in an inhibition of cell migration.

CONCLUSION

Human chymase causes the proteolysis of occludin and fibronectin, resulting in a decrease of barrier function and inhibition of the migration of corneal epithelial cells.

Vernal conjunctivitis

Vernal conjunctivitis is a bilateral, seasonal, external ocular inflammatory disease of unknown cause. Afflicted patients experience intense itching, tearing, photophobia, and mucous discharge, and usually demonstrate large cobblestone papillae on their superior tarsal conjunctiva and limbal conjunctiva. It primarily affects children, may be related to atopy, and has environmental and racial predilections. Although usually self-limited, vernal conjunctivitis can result in potentially blinding corneal complications. Treatment of chronic forms of ocular allergies may necessitate collaborative efforts between the ophthalmologist and the allergist or immunologist.

Differential diagnoses of conjunctivitis for clinical allergist-immunologists

OBJECTIVE

To provide a clinical overview of the types of conjunctivitis that are encountered by practicing clinical allergist-immunologists.

DATA SOURCES

Published literature in peer reviewed journals found in the National Library of Medicine (PubMed) database using the keywords ocular allergy and/or allergic conjunctivitis.

STUDY SELECTION

Studies related to ocular allergy and/or allergic conjunctivitis were selected for inclusion in this review.

RESULTS

Four clinical scenarios are presented that mimic frequently encountered inflammatory disorders that present as red eyes.

CONCLUSIONS

The signs and symptoms associated with the various inflammatory conditions affecting the conjunctiva often overlap and need to be differentiated to maximize care for patients with conjunctivitis.

The central role of conjunctival mast cells in the pathogenesis of ocular allergy

Ocular allergic diseases are characterized by specific activation of conjunctival mast cells with subsequent release of preformed and newly formed mediators. Mast-cell numbers on the ocular surface are increased in all forms of allergic conjunctivitis. Mast-cell activation plays a central role in the development of the ocular allergic reaction, which can be divided into an early and a late inflammatory phase. Mast-cell mediators have been measured in tears of patients suffering from various forms of allergic conjunctivitis, and in sensitized patients after specific ocular allergen challenge. Histamine and tryptase are the most studied mediators in tears of allergic patients. Several cytokines, such as IL-4 and TNF-a, are also produced and released by conjunctival mast cells, and probably play a role in the immunoregulation on the ocular surface. In vitro studies of the characteristics and biologic functions of conjunctival mast cells highlight their central role in the pathogenesis of ocular allergy, and have led to new opportunities to evaluate anti-allergic compounds. This review discusses the role of conjunctival mast cells in the development of ocular allergic diseases.

Evaluation of human conjunctival epithelium by a combination of brush cytology and flow cytometry: an approach to the quantitative technique

Cytology using the brush technique is readily available and is a rapid means of establishing a presumptive diagnosis of ocular surface changes. However, those techniques have some limitations when obtaining cells from certain localized areas particularly if using the Cytobrush-S. We have described here a new type of brush (Accellon-M), which can collect the local cells using its spherical tip, and evaluated them by comparing with Cytobrush-S. Furthermore, we differentiated epithelial cells from nonepithelial cells that were collected by brushing, and by a combination of brush cytology and flow cytometry using an anti-keratin antibody, AE-3, which reacts with all basic epithelial keratins. Accellon-M could collect the epithelial cells from conjunctiva as effectively as with the Cytobrush-S, and there were no statistical differences between both groups. AE-3, which is reported as the marker of epithelial cells, were detected quantitatively by a combination of brush cytology and flow cytometry techniques. The result of the present study emphasizes that both the Cytobrush-S and the Accellon-M are valuable for conjunctival brush cytology. An additional positive feature of the Accellon-M may be improved cell collection from the conjunctival epithelium especially when the target cells are in a limited area. The combination of the brush cytology and the flow cytometry technique appears to be a useful adjunct as an additional diagnostic or research tool for use in the detection of various antigens in the conjunctival epithelium.

Efficacy of lodoxamide eye drops on mast cells and eosinophils after allergen challenge in allergic conjunctivitis

PURPOSE

The purpose of the study is to evaluate in a double-blind, randomized study the efficacy of lodoxamide tromethamine 0.1% versus placebo.

METHODS

Signs and symptoms, tear tryptase, and tear fluid cytology were evaluated in 20 asymptomatic subjects with allergic conjunctivitis. The study included three allergen challenges in skin test-positive patients. At the first visit, a threshold dose of allergen was established. At the second visit, a bilateral ocular challenge was performed without pretreatment. At the third visit, either lodoxamide or placebo eye drops were used for 1 week before ocular challenge.

RESULTS

Lodoxamide significantly reduced tryptase levels (P < 0.01), neutrophils (P < 0.04), and eosinophils (P < 0.01) in the tear fluid and significantly inhibited ocular itching (P < 0.02) when compared with that of placebo.

CONCLUSIONS

Lodoxamide is effective in reducing tryptase levels and the recruitment of inflammatory cells in the tear fluid after allergen challenge.

Tear tryptase levels and allergic conjunctivitis

We measured tryptase, a neutral protease stored in the secretory granules of mast cells, by solid-phase radioimmunoassay in tears of 12 subjects with vernal keratoconjunctivitis (VKC) during remission phases, nine subjects with seasonal or perennial allergic conjunctivitis, and eight healthy controls. Mean values of tear tryptase levels were significantly (P < 0.02) increased in VKC patients (14.5 +/- 13 micrograms/l) when compared to those measured in patients with seasonal or perennial allergic conjunctivitis (0.6 +/- 0.1 microgram/l) and in controls (3.3 +/- 3.2 micrograms/l). In subjects with allergic conjunctivitis, the levels of tryptase, almost undetectable before allergen conjunctival challenge, showed a significant increase in the challenged eye 20 min-but not 6 h-after provocation in 5/9 cases. Our results indicate that VKC a severe ocular disease characterized by an increased number and abnormal distribution of mast cells in the conjunctiva, also shows elevated levels of tryptase in tears even during remission phases. Evidence of mast-cell activation, as revealed by a significant increase of tryptase levels in tears, in documented during the early-phase reaction, but not during the late-phase reaction, of allergic conjunctivitis patients challenged topically by specific allergen.