Differential CD4+ T‐cell responses of allergic and non‐allergic subjects to the immunodominant epitope region of the horse major allergen Equ c 1

The responses of allergen‐specific CD4⁺ T cells of allergic and healthy individuals are still incompletely understood. Our objective was to investigate the functional and phenotypic properties of CD4⁺ T cells of horse‐allergic and healthy subjects specific to the immunodominant epitope region of the major horse allergen Equ c 1. Specific T‐cell lines (TCLs) and clones were generated from peripheral blood mononuclear cells with Equ c 1_143–160, the peptide containing the immunodominant epitope region of Equ c 1. The frequency, proliferative response, cytokine production and HLA restriction of the cells were examined. The frequency of Equ c 1‐specific CD4⁺ T cells was low (approximately 1 per 10⁶ CD4⁺ T cells) in both allergic and non‐allergic subjects. The cells of allergic subjects had a stronger proliferative capacity than those of non‐allergic subjects, and they predominantly emerged from the memory T‐cell pool and expressed the T helper type 2 cytokine profile, whereas the cells of non‐allergic subjects emerged from the naive T‐cell pool and produced low levels of interferon‐γ and interleukin‐10. T‐cell response to Equ c 1_143–160 was restricted by several common HLA class II molecules from both DQ and DR loci. As the phenotypic and functional properties of Equ c 1‐specific CD4⁺ T cells differ between allergic and non‐allergic subjects, allergen‐specific T cells appear to be tightly implicated in the development of diseased or healthy outcome. Restriction of the specific CD4⁺ T‐cell response by multiple HLA alleles suggests that Equ c 1_143–160 is a promising candidate for peptide‐based immunotherapy.