Role of chemokines in 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.

Adult vernal keratoconjunctivitis

PURPOSE OF REVIEW

Vernal keratoconjunctivitis (VKC) is a rare chronic self-limiting allergic inflammatory disease of the ocular surface mostly affecting young boys in their first decade of life. In the last few years a new clinical entity of VKC has been described: adult VKC. Two variants have been identified according to clinical onset: early (childhood VKC persisting beyond puberty) and late onset (arising de novo in adults) adult VKC. Several epidemiologic studies on VKC have been published from single tertiary centers but while the age distribution of VKC patients does show a small percentage of adults with the disease, detailed analysis on this small subset of adult VKC cases is lacking. In this review we describe pathogenesis, clinical features, diagnostic alternatives, and therapeutic alternatives of this highly invalidating disease.

RECENT FINDINGS

Adult variants of VKC have same clinical manifestations of classic form, but show higher inflammatory response and increased risk of chronic fibrotic sequelae.

SUMMARY

Adult VKC research could provide insights on the impact of sex hormones in the pathogenesis of allergic diseases and on the mechanisms of inflammation and fibrosis, which cause potentially vision threatening sequelae. The present review will highlight the recent developments in our understanding of this uncommon entity.

[Ocular allergies]

Recent developments indicate that ocular allergy is more than an IgE-mediated allergic conjunctivitis. Ocular allergy is a disease affecting the entire ocular surface including conjunctiva, lids, cornea, lacrimal gland and tear film. Besides an IgE-mediated reaction, a complex chronic inflammation is involved in the pathogenesis of many ocular allergies. According to their pathogenesis and clinical picture, ocular allergies are classified into mild forms, such as seasonal and perennial allergic conjunctivitis as well as giant papillary conjunctivitis, and chronic, potentially blinding forms such as atopic keratoconjunctivitis and vernal keratoconjunctivitis. New therapeutics act on the entire inflammatory process or try to modulate the allergic reaction early and specifically. The association with non-ocular allergic symptoms requires an interdisciplinary approach.

Animal models of allergic and inflammatory conjunctivitis

Allergic eye diseases are complex inflammatory conditions of the conjunctiva with an increasing prevalence and incidence. The diseases are often concomitant with other allergic diseases such as allergic rhinitis, atopic dermatitis and allergic asthma. Despite the disabling and prominent symptoms of ocular allergies, they are less well studied and further insights into the molecular basics are still required. To establish new therapeutic approaches and assess immunological mechanisms, animal models of ocular allergies have been developed in the past years. The major forms of allergic ocular diseases, seasonal and perennial allergic conjunctivitis, vernal and atopic keratoconjunctivitis and giant papillary conjunctivitis, each have different pathophysiological and immunological components. In contrast to these distinct entities, the current animal models are based on the sensitization against a small number of allergens such as ovalbumin, ragweed pollen or major cat allergens and consecutive challenge. Different animal species have been used so far. Starting with guinea-pig models of allergic conjunctivitis to assess pharmacological aspects, new models including rats and mice have been developed which mimic major features of ocular allergy. The presently preferred species for the investigation of the immunological basis of the disease is represented by murine models of allergic conjunctivitis. In the future, combined ocular, nasal and aerosolic challenges with allergens may provide a model of allergy that encompasses simultaneously the target organs eye, nose and airways with conjunctivitis, rhinitis and asthma.

Allergic chronic inflammation of the ocular surface in vernal keratoconjunctivitis

PURPOSE OF REVIEW

The purpose of this review is to describe the new immunopathologic features of vernal keratoconjunctivitis: the involvement of cytokines, growth factors, cells, mediators and neurotransmitters, as well as the mechanism leading to tissue remodelling.

RECENT FINDINGS

Vernal keratoconjunctivitis is an allergic eye disease affecting young boys living in a warm climate. It is characterized by conjunctival giant papillae, hyperemia and frequent involvement of the cornea. Approximately 50% of the patients with vernal keratoconjunctivitis do not have a family or medical history of atopic diseases, and do not show IgE sensitization, suggesting that this disease is not solely IgE mediated. Vernal keratoconjunctivitis is a Th2 lymphocyte driven disease with a Th2 cytokine derived pattern, increased levels of mRNA for IL-3, IL-4, IL-5 and IL-13. Th2 lymphocytes induce IgE hyperproduction, activation of mast cells, eosinophils, neutrophils and their toxic products. An overexpression of adhesion molecules, RANTES, eotaxin and metalloproteinases contribute to chronic inflammation. A role for substance P and nerve growth factor has been postulated, as well as for other growth factors (epidermal growth factor, fibroblast growth factor and transforming growth factor beta 1) that induce fibroblast growth and new collagen production. Recent studies have also pointed out the role of resident conjunctival cells, such as epithelial cells and fibroblasts, in the inflammatory and remodelling process of vernal keratoconjunctivitis. The pathogenesis of the condition is probably multifactorial, with the interaction of the immune, nervous and endocrine systems.

SUMMARY

Vernal keratoconjunctivitis is a chronic inflammatory and potentially blinding disease. Understanding of the complex interactions and cross talk between cells, cytokines and other mediators is relevant for new therapeutic approaches.