Objectives: Evidence suggests eosinophils may be acting as antigen-presenting cells (APCs) by presenting antigen to T cells. We investigated the surface proteins of eosinophils and T cells in the esophageal biopsies of patients with eosinophilic esophagitis (EoE), patients with gastroesophageal reflux disease (GERD), and healthy controls (HCs).
Methods: Subjects were categorized as EoE, GERD, or HC. In esophageal tissue, EG2+ eosinophils were stained for the APC markers, CD40 or CD80, via immunohistochemistry. CD3+ T cells were stained for costimulatory markers, CD40L or CD28, and for activation markers, CD69 or CD134, via immunofluorescence or immunohistochemistry.
Results: Eosinophils stained with CD40 and CD80. The number of EG2+CD40+ cells was increased in EoE (mean 19.1 ± 14.8 cells/high-power field [HPF], n = 11), compared with GERD (mean 0.13 ± 0.19 cells/HPF, n = 5, P < 0.01) and HC (mean 0.3 ± 0.7 cells/HPF, n = 5, P < 0.01). There was an elevation in EG2+CD80+ cells in EoE (mean 18.1 ± 16.2 cells/HPF, n = 10), GERD (mean 1.7 ± 2.8 cells/HPF, n = 6, P < 0.01), or HC (mean 0.8 ± 1.3 cells/HPF, n = 6, P < 0.01). CD3+ T cells stained with CD40L (not quantified). CD3+ T cells stained with CD28 at elevated levels in EoE (mean 14 ± 8.7 cells/HPF, n = 9) versus GERD (mean 3.3 ± 1.2 cells/HPF, n = 6, P < 0.05) or HC (mean 3.0 ± 3.2 cells/HPF, n = 7, P < 0.01). The number of CD3+CD69+ cells was highest in EoE (mean 14.8 ± 7.5 cells/HPF, n = 6) versus GERD (mean 0.8 ± 0.9 cells/HPF, n = 6, P < 0.001) or HC (mean 2.7 ± 2.5 cells/HPF, n = 6, P < 0.001).
Conclusions: We show that esophageal eosinophils express CD40 and CD80, and T cells with CD40L, CD28, and CD69. The number of double-stained cells was higher in EoE in comparison to control groups. These data support the hypothesis that eosinophils in EoE may act as APCs, activating T cells.