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