Lung-resident eosinophils represent a distinct regulatory eosinophil subset

Area of Science:

• Immunology
• Respiratory Medicine
• Allergy Research

Background:

• Eosinophils are linked to infections and allergic diseases like asthma, but also play homeostatic roles.
• The function of normal lung-resident eosinophils (rEos) in mice remains uncharacterized.
• Distinguishing between resident and inflammatory eosinophil subsets is crucial for understanding lung immunity.

Purpose of the Study:

• To characterize the function of resident pulmonary eosinophils (rEos) in mice.
• To differentiate rEos from inflammatory eosinophils (iEos) during allergic airway inflammation.
• To investigate the role of rEos in regulating T-helper 2 (Th2) cell responses and dendritic cell (DC) maturation.

Main Methods:

• Phenotypic analysis of pulmonary eosinophils using cell surface markers (Siglec-F, CD62L, CD101) and nuclear morphology.
• Assessment of IL-5 dependency for eosinophil populations.
• Gene expression profiling to compare rEos and iEos.
• Mouse models of house dust mite-induced allergic airway inflammation.
• Studies on the interaction between eosinophils and allergen-loaded dendritic cells (DCs).
• Comparison of murine eosinophil populations with human lung and sputum eosinophils.

Main Results:

• Steady-state pulmonary rEos are IL-5-independent, parenchymal cells (Siglec-FintCD62L+CD101lo) with ring-shaped nuclei.
• During allergic reactions, rEos persist unchanged alongside IL-5-dependent, peribronchial inflammatory eosinophils (iEos) (Siglec-FhiCD62L-CD101hi) with segmented nuclei.
• rEos exhibit a more regulatory gene expression profile than iEos.
• Mice lacking lung rEos show heightened Th2 cell responses to allergens.
• rEos, but not iEos, inhibit the maturation and pro-Th2 function of allergen-loaded DCs.
• Murine rEos are phenotypically similar to human lung eosinophils, while iEos resemble human asthmatic sputum eosinophils.

Conclusions:

• Lung rEos represent a distinct eosinophil subset with critical homeostatic functions.
• rEos play a key role in suppressing Th2 immune responses by modulating dendritic cell function.
• These findings in mice have relevance to human lung immunity and eosinophilic diseases like asthma.