Vazquez-Mera_2024_Allergy__

BACKGROUND: Asthma pathology may induce changes in naive/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), CD26(int) and CD26(hi) subsets within different lymphocyte populations. METHODS: The proportion of CD26(-/lo), CD26(int) and CD26(hi) subsets within CD4(+) effector T cells (T(eff)), total CD4(-) lymphocytes, gammadelta-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) T(eff) cell subset by LC-MS/MS and immunofluorescence. RESULTS: Cluster 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(-)CD26(hi) cells, which negatively correlated with systemic inflammation. Eosinophilic asthma displayed a general expansion of CD26(-/lo) subsets. Specifically, CD4(+)CD26(-/lo) T(eff) expansion was confirmed in asthma, especially in atopic patients. Proteomic characterisation of this subset with a T(EM)/T(EMRA) 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) T(eff) compared to CD4(+) T lymphocytes. CONCLUSION: There is an association between CD26 levels in different lymphocyte subsets and asthma phenotype/severity. CD4(+)CD26(-/lo)T(EMRA) cells expressing innate proteins specific to eosinophils/neutrophils could be determinant in sustaining long-term inflammation in adult allergic asthma.