Artepillin C induces eosinophil apoptosis and differentiation of monocytic myeloid-derived suppressor cells (M-MDSC) expressing indolamine 2,3-dioxygenase 1 (IDO) in the pulmonary allergic inflammation

Asthma is a chronic lung inflammatory disease and eosinophil influx is one of the main hallmarks of the disease. Artepillin C (ArtC), a major compound of green propolis, is described as an anti-inflammatory compound. Using ovalbumin (OVA)-induced asthma model, our group already showed that ArtC reduces eosinophil influx, lung inflammation and mucus production by induction of monocytic myeloid derived suppressor cells (M-MDSC). However, the mechanisms by which ArtC-induced M-MDSC reduce pulmonary inflammation are unclear. We hypothesized that ArtC-induced M-MDSC reduces airway inflammation through IDO expression and directly induces apoptosis in eosinophils after allergen exposure. To evaluate the pro-apoptotic effect of ArtC, lung cells from mice exposed to OVA were cultivated in vitro with ArtC for 24 hours. After stimulation with ArtC, eosinophils, evaluated by flow cytometry, exhibited an increase in late apoptosis cell death (CD11b+SiglecF+AnnexinV+Live/Dead+ cells). ArtC treatment in vitro increased the differentiation of M-MDSC under GM-CSF plus IL-6 culture for 96h. A second stimulation (boost) in vitro of MDSC with ArtC significantly increased the expression of IDO in those cells compared to non-treated cells and to those cells under differentiation (96h). M-MDSC were also differentiated in the presence or absence of ArtC for 96 hours and co-cultivated with splenocytes from OT-II mice. After Ova323-339 peptide stimulation, ArtC-induced MDSC inhibited T CD4+ cell proliferation. Our results show that ArtC might negatively regulate pulmonary inflammation by two possible mechanisms: T cell inhibition by induction of IDO in M-MDSC and induction of apoptosis in eosinophils. Therefore, ArtC might represent a novel adjuvant therapy for patients with asthma. Financial support: FAPESP grants 2017/21629-5; 2022/16716-4. Ethics committee aproval: CEUA protocol 1203/2023.