Effective antigen presentation to helper T cells by human eosinophils

Area of Science:

• Immunology
• Cell Biology

Background:

• Eosinophils, traditionally viewed as inflammatory cells, are increasingly recognized for their immunomodulatory functions.
• While murine eosinophils can present antigens to CD4+ T helper (Th) cells, this capability in human eosinophils remains largely unexplored.

Purpose of the Study:

• To investigate whether human eosinophils can present various antigens, including allergens, to activate Th cells.
• To characterize the expression of MHC class II and co-stimulatory molecules by human eosinophils, which are crucial for antigen presentation.

Main Methods:

• Human peripheral blood eosinophils from non-allergic donors were isolated and pulsed with antigens: house dust mite extract (HDM), Timothy Grass extract (TG), or Mycobacterium tuberculosis purified protein derivative (PPD).
• Eosinophils were co-cultured with autologous CD4+ Th cells to measure proliferative and cytokine responses.
• Flow cytometry was used to determine eosinophil expression of HLA-DR/DP/DQ and co-stimulatory molecules (CD40, CD80, CD86).

Main Results:

• Eosinophils pulsed with HDM, TG, or PPD stimulated Th cell proliferation in a dose-dependent manner.
• Cytokine responses were variable across donors and antigens, often showing a mix of pro- and anti-inflammatory cytokines, without a bias towards specific Th subsets.
• Eosinophils upregulated surface expression of HLA-DR/DP/DQ, CD80, CD86, and CD40 during culture, sustained for up to 5 days when incubated with antigens like HDM or its major allergens (Der p I, Der p II).

Conclusions:

• Human eosinophils function as effective antigen-presenting cells (APCs) capable of stimulating diverse Th cell responses.
• This antigen-presenting capacity against a range of antigens, including allergens, may play a significant role in the pathogenesis of allergic diseases.