Exploring CD26^−/lo subpopulations of lymphocytes in asthma phenotype and severity: A novel CD4⁺ T cell subset expressing archetypical granulocyte proteins

Abstract

BackgroundAsthma pathology may induce changes in naïve/memory lymphocyte proportions assessable through the evaluation of surface CD26 (dipeptidyl peptidase 4/DPP4) levels. Our aim was to investigate the association of asthma phenotype/severity with the relative frequency of CD26−/lo, CD26int and CD26hi subsets within different lymphocyte populations.MethodsThe proportion of CD26−/lo, CD26int and CD26hi subsets within CD4+ effector T cells (Teff), total CD4− lymphocytes, γδ‐T cells, NK cells and NKT cells was measured in peripheral blood samples from healthy (N = 30) and asthma (N = 119) donors with different phenotypes/severities by flow cytometry. We performed K‐means clustering analysis and further characterised the CD4+CD26−/lo Teff cell subset by LC–MS/MS and immunofluorescence.ResultsCluster analysis including clinical and flow cytometry data resulted in four groups, two of them with opposite inflammatory profiles (neutrophilic vs. eosinophilic). Neutrophilic asthma presented reduced CD4−CD26hi cells, which negatively correlated with systemic inflammation. Eosinophilic asthma displayed a general expansion of CD26−/lo subsets. Specifically, CD4+CD26−/lo Teff expansion was confirmed in asthma, especially in atopic patients. Proteomic characterisation of this subset with a TEM/TEMRA phenotype revealed upregulated levels of innate (e.g. MPO and RNASE2) and cytoskeleton/extracellular matrix (e.g. MMP9 and ACTN1) proteins. Immunofluorescence assays confirmed the presence of atypical proteins for CD4+ T cells, and an enrichment in ‘flower‐like’ nuclei and MMP9/RNASE2 levels in CD4+CD26−/lo Teff compared to CD4+ T lymphocytes.ConclusionThere is an association between CD26 levels in different lymphocyte subsets and asthma phenotype/severity. CD4+CD26−/loTEMRA cells expressing innate proteins specific to eosinophils/neutrophils could be determinant in sustaining long‐term inflammation in adult allergic asthma.