Immunophenotyping of immune cells
Allergic sensitization is associated with multiple changes in blood
immune cells,175 and high dimensional
immunophenotyping using flow- and mass spectrometry (i.e. Cytometry Time
of Flight; CyTOF) has contributed greatly to this
identification.237 A study on bee venom AIT provided
detailed characterization of allergen-specific B cells before and after
bee venom tolerance in allergic patients and bee-keepers with Api m 1
-specific B cells showing increased CCR5 expression after high-dose
allergen exposure.238 In a study of OIT for milk
allergy, researchers found, using flow cytometry, a significant increase
in blood invariant natural killer cells and a shift from a type 2
T-helper (Th-2; i.e. IL-4, IL-13) to a Th-1 (ie IFN-γ) cytokine
profile.239 Similar studies in other immunotherapy
models can assist with determining potential biomarkers for monitoring
AIT.
Recent evidence shows that AIT modulates the balance between circulating
T follicular helper (Tfh) and regulatory cells (Tfr), with Tfr as a
potential biomarker for AIT efficacy.240,241Upregulation of the activated allergen‐specific Tregs and downregulation
of dysfunctional allergen‐specific Treg cell subset, associated with
improved clinical response, were recently
described.242 Responder status was shown to be
associated with increased frequency of IgA- and IgG4-expressing allergen
specific B cells, plasmablasts, and IL-10+ and/or IL-1RA+ Breg
cells.243
AIT-induced T regulatory cells secreting IL-35 (iTR35) cells promote
production of IL-10 from CD19+ B cells, Breg subsets and Tfr
cells.244 Circulating Tfr cells share properties of
memory cells and are distinct from their lymph nodes (LN) counterpart as
they suppress B and Tfh cells with a much lower capacity, while
circulating memory-like Tfh cells are more potent than LN effector Tfh
cells.245 In addition, circulating memory-like Tfr
cells persist for long periods, thus they could support the long-term
immunomodulatory effect of peptide AIT. Functional evaluation of T
regulatory cells via expression of Glycoprotein A repetitions
predominant (GARP) and Special AT-rich sequence binding protein 1
(SATB1) is also interesting as a future potential biomarker. Tregs
uniquely express GARP on their cell surface and GARP functions as a
delivery system for latent TGF-β, which might augment the
immunosuppressive role of Tregs on effector cells.246GARP expression was described as an activation marker of parasitic
infection induced Tregs that strongly suppress allergic inflammation,
thus is a novel potential mechanistic pathway for AIT. SATB1 is a genome
organizer protein expressed in a lineage specific manner in CD4+
T-cells. During the early Th2 cell differentiation, IL-5 expression is
repressed through direct binding of SATB1 to the IL-5 promoter. Thus,
SATB1 modulation might expand the impact of AIT on eosinophilic
inflammation. In addition, SATB1-dependent Treg-cell specific
super-enhancers activation is crucial for Treg cell lineage
specification in the thymus