Abstract
Background: From early life, respiratory viruses are implicated in the
development, exacerbation and persistence of respiratory conditions such
as asthma. Complex dynamics between microbial communities and host
immune responses, shape immune maturation and homeostasis, influencing
health outcomes. We evaluated the hypothesis that the respiratory virome
is linked to systemic immune responses, using peripheral blood and
nasopharyngeal swab samples from preschool-age children in the PreDicta
cohort.
Methods: Peripheral blood mononuclear cells from 51 children (32
asthmatics, 19 healthy controls), participating in the 2-year
multinational PreDicta cohort were cultured with bacterial
(Bacterial-DNA, LPS) or viral (R848, Poly:IC, RV) stimuli. Supernatants
were analyzed by Luminex for the presence of 22 relevant cytokines.
Virome composition was obtained using untargeted high troughput
sequencing of nasopharyngeal samples. The metagenomic data were used for
the characterization of virome profiles and the presence of key viral
families (Picornaviridae, Anelloviridae, Siphoviridae). These were
correlated to cytokine secretion patterns, identified through
hierarchical clustering and principal component analysis.
Results: High spontaneous cytokine release was associated with increased
presence of Prokaryotic virome profiles and reduced presence of
Eukaryotic and Anellovirus profiles. Antibacterial responses did not
correlate with specific viral families or virome profile, however, low
antiviral responders had more Prokaryotic and less Eukaryotic virome
profiles. Anelloviruses and Anellovirus-dominated profiles were equally
distributed amongst immune response clusters. The presence of
Picornaviridae and Siphoviridae was associated with low interferon-λ
responses. Asthma or allergy did not modify these correlations.
Conclusions: Antiviral cytokines responses at a systemic level reflect
the upper airway virome composition. Individuals with low innate
interferon responses have higher abundance of Picornaviruses (mostly
Rhinoviruses) and bacteriophages. Bacteriophages, particularly
Siphoviridae appear to be sensitive sensors of host antimicrobial
capacity, while Anelloviruses are not affected by TLR-induced immune
responses.
Keywords: Asthma, bacteriophages, Interferon-λ, Rhinoviruses, virome
Introduction
The role of the microbiome in shaping health and disease is increasingly
understood and substantiated [1]. Nevertheless, the focus on the gut
microbiome has left other important niches, such as the respiratory
tract, or agents, such as viruses, less well studied [2].
Particularly, little is known about the role of the respiratory virome
in homeostasis across the ages, despite several studies showing that
common respiratory viruses can often be found in the airways of
asymptomatic individuals [3,4].
It has been suggested that the virome may be able to mold the immune
system, affecting the development of asthma and respiratory diseases in
childhood [5]. Specific viruses, or viral families may be able to
modulate the immune responses and hence drive immune maturation,
influence health and disease and be candidates for intervention
strategies [6]. Clearly, infection with common cold viruses is
closely linked with the development of respiratory and other allergic
diseases [7,8].
In addition, to maintain homeostasis the immune system needs to control
the density and composition of the microbiome [9]. When it comes
specifically to the respiratory virome, much less is known,
nevertheless, there is increasing understanding regarding the
development of immune surveillance to eukaryotic viruses [10], the
interplay between inert viruses such as the Anelloviruses and immune
competence [11] and the non-host immune support conveyed by
bacteriophages [12].
It is therefore clear that a continuous interplay between immune
surveillance, established microbial self and incoming microbes, defines
a dynamic balance shaping health and disease in an interactive
complexity, in which the local virome has a considerable share.
We have previously described the respiratory virome (DNA and RNA
viruses) in a cohort of well-characterized preschool-age children with
asthma and healthy controls across Europe, in the context of the
PreDicta study [13]. Among the viral genomes identified, the most
prevalent and diversified between health and asthma, involved
Picornaviruses, Anelloviruses and bacteriophages of the Siphoviridae
family. Depending on their virome composition, individuals could be
grouped into three profiles: a Eukaryotic prevailing profile (E-VPG), an
Anellovirus prevailing profile (A-VPG) and a Prokaryotic prevailing
profile (P-VPG).
We hypothesized that any biological interactions between the respiratory
virome and the host antiviral immune responses may be reflected in
associations between viral and immune signatures. The aim of this study
was to evaluate links between the presence of the prevailing viral
families, as well as of the respiratory virome profile groups, with
cytokine production from peripheral blood cells at baseline and
following stimulation with viral- and bacterial-mimicking stimuli.
This helps characterize immune-microbiome interactions and biomarkers
that identify health/disease gradients and unravel novel therapeutic
targets.