Human memory CD4+ T cell response to the major dog allergen Can f 5, prostatic kallikrein

Abstract

Background Human CD4+ T cell responses to important animal allergens are still insufficiently understood. Objective To comprehensively characterize in vitro and ex vivo the peripheral blood memory CD4+ T cell responses of subjects with and without allergy to the major dog allergen Can f 5, the only known animal allergen in the kallikrein family of proteins. Methods Can f 5-specific memory CD4+ T cell lines (TCLs) were established from the peripheral blood of 12 subjects with and 12 subjects without allergy to Can f 5 and characterized for their functional and phenotypic properties. The results were evaluated with those obtained ex vivo with a novel CD154 enrichment method. The epitopes recognized by the Can f 5-specific TCLs were determined with 72 overlapping 16-mer peptides covering the sequence of the allergen. Results Can f 5-specific TCLs were obtained at about tenfold higher frequency from allergic than from non-allergic subjects. Functionally, the TCLs of allergic subjects displayed a Th2-biased cytokine phenotype and increased T cell receptor avidity, whereas the TCLs of non-allergic subjects displayed a Th1-/Th0-biased cytokine phenotype and lower TCR avidity. The higher frequency and the Th2 phenotype of Can f 5-specific memory CD4+ T cells in allergic subjects were confirmed by the CD154 enrichment method ex vivo. Six distinct T cell epitope regions of Can f 5 were predominantly recognized by the TCLs from allergic subjects. Conclusions and Clinical Relevance Can f 5-specific memory CD4+ T cell responses differ considerably between subjects with and without allergy, as assessed by both in vitro and ex vivo approaches. Peptides containing the dominant T cell epitopes of Can f 5 can be employed for developing peptide-based immunotherapy for dog allergy.

Antigen-specific regulatory T-cell responses against aeroantigens and their role in allergy

“…In healthy donors allergenreactive T cells mainly displayed a naive phenotype, low avidity, and lack of clonal expansions. 18,60,65,84 Allergen-specific Tcons from healthy donors did also not express Ki-67 during allergen season, a marker of recent in vivo activation, 18 which can clearly be detected in allergic donors. 18,51 Interestingly, the direct ex vivo analysis of birch pollen-reactive Tcons and Tregs demonstrated a clonally expanded, high-affinity Ki-67+ Treg population, specifically against particle-associated proteins but not against the soluble fraction, containing the main allergens such as Betv1.…”

“…18,22,51,52,116 Indeed, the frequencies of allergen-specific T cells in healthy donors were in the range of 1-10/10e6 CD4+ T cells, similar to the frequencies of T cells specific for neoantigens. 73,74 TCR sequencing 18 and avidity measurement 18,60,61,65,84 also revealed clonally expanded, high-avidity memory T cells only in allergic donors. In healthy donors allergenreactive T cells mainly displayed a naive phenotype, low avidity, and lack of clonal expansions.…”

“…53 As outlined above, the affinities and frequencies of allergen-specific Tcons significantly differ between healthy and allergic donors. 18,22,46,48,49,51,52,60,61,65,84,116 Thus, the reduced suppressive activity observed in some studies may also reflect a stronger Th2 activation in patients. Indeed, in an antigen-specific in vitro suppression assay CD25+ Tregs during birch pollen season were unable to suppress birch-specific Th2 responses, whereas Th1 cells were readily suppressed.…”

“…22,73 Several studies have used the CD154 enrichment approach to detect allergen-specific Tcons in healthy and allergic donors. 18,46,48,49,84 In combination with CD137 as activation marker for Tregs, a first comprehensive analysis of Tregs specific for several tolerogenic and pathogenic exogenous antigens in humans was possible. 18 However, per definition, stimulationdependent analyses miss the detection of anergic antigenspecific T cells, which might be induced by SIT.…”

“…Thus, to resolve in vivo-expanded antigen-specific memory responses, additional parameters, such as TCR repertoire and avidity measurements of antigen-specific T cells are required. 18,60,61,65,84 Animal models for analysis of T-cell responses against inhaled antigens in vivo Animal experiments contributed significantly to our knowledge about priming and differentiation of T cells against inhaled antigens and allergy development. Induction of various Treg subsets has been described, including CD25+ cells 87 or Foxp3+ Tregs, 88-91 IL-10 36,92,93 , or transforming growth factor-β/latencyassociated peptide-expressing T cells.…”