Introduction
Microorganisms colonize the ocular mucosa, where they promote pathogen immunity by facilitating inflammatory cell recruitment (1). Recent microbiome studies using DNA amplicon sequencing have revealed that the healthy human ocular surface (OS) has a more diverse and relatively consistent microbial population than previously determined by conventional culture-based studies (2-6). Similarly, the OS fungal microbiome of healthy individuals showed a greater degree of diversity than reported with conventional cultivable methods, observing that several fungal genera were associated with the healthy conjunctiva (7). Moreover, other studies have shown that microbiome on the conjunctival surface is different from the deeper tissue, suggesting that there is a spatially stratified conjunctival microbiota (8, 9).
There is an increasing interest in the role of the conjunctival microbiome in different ocular surface diseases, such as meibomian glans dysfunction (10), dry eye (11, 12), contact lens wear (13), Steven-Johnson Syndrome (14), bacterial and fungal keratitis (15). An influence of the gut microbiota to the development of autoimmune diseases, including uveitis (16) and dry eye (17), has been also demonstrated. There is evidence that there is a link between microbes and the development of allergic diseases, suggesting that dysregulation of resident microbial communities (dysbiosis) might be associated with allergy risk (18-20). It is still uncertain if and how the ocular surface microbiome influences ocular allergy (OA).
Vernal keratoconjunctivitis (VKC) is a severe form of OA affecting mostly male children and young adults with a typical relapsing-remitting course, seasonal recurrences and potentially visual impairments. The aetiology of VKC may involve a variety of factors, such as genetic predispositions, environmental allergens, climate changes and both IgE- non IgE mediated hypersensitivities (21). Th2-cells, T2-type cytokines, pro-inflammatory cytokines, a variety of chemokines, growth factors, and enzymes are over-expressed in VKC patients (22, 23). We recently found and overexpression of multiple pattern recognition receptors (PRRs) in VKC patients suggesting that host-microbe interaction play a role in VKC pathogenesis (24). What is currently not known is whether VKC patients have a different microbial composition compared to healthy individuals and how these differences correlate with signs and symptoms. To investigate the VKC-associated ocular microbiome, we applied 16S and ITS2 amplicon sequencing. Understanding the patterns of the connection between the ocular microbiome and VKC development will help in understanding causes of this disease and will improve current therapies.
Materials and Methods