Alveolar Macrophages From House Dust Mite-Tolerant Mice Induce Foxp3+Regulatory T Cells In An Il-10-Independent Manner

Alveolar macrophages (AMs) are critical for maintaining immune tolerance in the lung. Previous studies have shown that naive AMs can induce Foxp3+ regulatory T cells (Tregs) but lose this ability when initially exposed to inhaled allergens, thereby promoting the development of asthma. The purpose of this study was to determine whether long-term exposure to inhaled house dust mite (HDM) improves the ability of AMs to induce Tregs. We have previously established that short-term (2 wk) HDM exposure induces allergic airway disease (AAD) whereas long-term (11 wk) exposure promotes tolerance to HDM (i.e. suppression of allergic inflammation with increases in pulmonary Tregs and IL-10+ AMs). AMs were sorted from the lungs of HDM-AAD (2 wk) and HDM-tolerant (11 wk) C57BL/6 mice and co-cultured with naïve CD4+Foxp3- T cells in the presence or absence of exogenous TGF-β and IL-10/IL-10R blockade for 72 hours. The percentage of induced Foxp3+ Tregs was then examined. AMs from HDM-tolerant mice induced significantly more Tregs than HDM-AAD mice (31% vs 14%, p <0.0001), suggesting that AMs adopt regulatory functions following long-term allergen exposure. This effect was dependent upon the addition of exogenous TGF-β and was not reversed following IL-10/IL-10R blockade (p = 0.15). These findings suggest that the generation of regulatory AMs following long-term HDM exposure may play an important role in the suppression of HDM-induced asthma through induction of Tregs. RNA sequencing studies are currently underway to determine the players involved in regulatory AM-mediated Treg induction, as these cells are a promising immunotherapeutic target for asthma.