Tropical urban environments reveal a strong association of
CD45RBloCD161+ Th2 subset to allergic rhinitis
To the Editor:
Allergic airway diseases such as allergic rhinitis (AR) affects more
than 400 million individuals worldwide and afflicts substantial health
and economic morbidity. [1] AR is
strongly associated with a type 2 response, characterized by the
cytokines IL-5, IL-4 and IL-13. However, the key drivers behind AR
immunopathogenesis remained to be elucidated. This study aims to
identify critical pathogenic cell populations associated with AR using
the Singapore System Immunology Cohort (SSIC)
[2] and a clinician-diagnosed
paediatric cohort with active AR manifestation
(Supplementary Table 1 ). In both cohorts, the
eosinophilic nature of AR was confirmed by higher blood eosinophil
numbers (Supplementary Figure 1 ).
Whole blood gene expression analysis revealed a total of 23 probes
representing 20 unique genes were associated with AR in the SSIC
(Table 1A ). To account for ethnicity and environmental
influences we validated our findings in BAMSE population-based cohort
comprising of Swedish adolescents. Table 1B shows 11 DEGs which
was also associated with AR, confirming the transferability of our
findings to other populations. For the top DEGs that reached nominal
significance in the SSIC we performed an Ingenuity Pathway Analysis
(IPA). Supplementary Table 2 revealed important pathways
related to hypersensitivity and inflammation and also functional
enrichment for eosinophils, basophils and mast cells. In particular,
functional activation of Th2 was highlighted as a key pathway for AR
pathogenesis. As CRTH2 was reported to be expressed by cell types
involved in the eosinophilic response,
[3] an unsupervised cluster analysis
was performed on the CRTH2+ subset in PBMC of individuals from SSIC
(Figure 1 A and B ) to determine CRTH2+ subsets associated with
AR. We found that CD161+Th2 subsets in particularly to be strongly
associated with AR (Figure 1C and D )
(Supplementary Figure 2 ). Further characterization found
that the marker CD45RB to be significantly downregulated on CD161+Th2
cells of AR individuals (Figure 1E ). Low CD45RB expression on T
cells is indicative of a mature phenotype. Interestingly, significantly
higher circulatory plasma IL-5 levels (Figure 1F) . Furthermore
we could also demonstrate AR individuals produced significantly higher
IL-5 in an in vitro PMA-stimulation assay (Figure 1G ).
While we noted a small population of IL-5 secreting conventional
CD161-Th2 (cTh2), IL-5 secretion was significantly elevated in CD161+Th2
cells (Figure 1H ). Strikingly, IL-5 was found to be
predominantly secreted by CD45RBlo subset in both cTh2
and CD161+Th2 (Figure 1H and I ). There was also a significant
increase in the IL-5 producing CD45RBloCD161+Th2
population from the AR individuals (Figure 1I ). These findings
confirm CD45RBloCD161+Th2 as the main producers of
IL-5.
We further validated our findings in a second paediatric cohort with
clinically diagnosed active AR manifestations. To further refine
CD161+Th2 subset that is associated with AR, we performed unsupervised
PhenoGraph and UMAP clustering on CD161+Th2 (Supplementary
Figure 3A and B ). Amongst the UMAP clusters, “cluster 3” was found
to be significantly associated with active AR
(Supplementary Figure 3C and D ). Deep characterization
reveals “cluster 3” to be an IL-5 secreting CD45RBlopopulation, confirming our earlier observation
(Supplementary Figure 3E ). Furthermore, this cluster
appeared to be a highly differentiated population of mature CD161+Th2
cells with an activated phenotype secreting IL-2, IL-3, IL-4, IL-9 and
IL-13 concomitantly (Supplementary Figure 3E and F ).
Thus, the severity of eosinophilic airway allergies such as AR seems to
be driven by an activated terminally differentiated CD161+Th2 subset
that is able to secrete a complex set of inflammatory cytokines.
The presence of CD45RBloCD161+Th2 population in both
cohorts shows the persistence and pertinence of this population in the
pathogenesis of AR. Both cohorts described in this study were collected
in Singapore, whereby majority of the individuals are sensitized against
HDM. HDM is a perennial allergen in tropical nations such as Singapore,
thus T cells in atopic individuals undergo constant stimulation. This
could explain the strong association observed between CD45RB expression
on CD161+Th2 cells and atopy markers despite the fact that not all
subjects demonstrated active AR symptoms during the collection of SSIC
cohort. Taken together, our current study unifies the markers previously
reported for allergic-specific Th2 subsets and provides clarity for the
pathogenic Th2 subset previously reported in different allergic
diseases.[4-6] Neutralizing the
CD45RBloCD161+Th2 subset should disrupt the allergic
response pathway, thus providing a target for lasting therapeutic
interventions. Moreover, these cells may also be leveraged as a
biomarker for the effectiveness of immunotherapy as well as a potential
biomarker of public health surveillance of allergic individuals.