Propolis from southeastern Brazil produced by Apis mellifera affects innate immunity by modulating cell marker expression, cytokine production and intracellular pathways in human monocytes

Objectives Propolis is a bee-made product used for centuries due to its diverse biological properties, including its immunomodulatory action. This work aimed at investigating whether propolis may affect monocyte functions challenged with retinoic acid (RA), B subunit of Escherichia coli heat-labile enterotoxin (EtxB), human melanoma-associated antigen-1 (MAGE-1) and lipopolysaccharide (LPS). Methods Monocytes from healthy donors were treated with the stimuli separately or in the presence of propolis. Cell viability was evaluated by MTT assay, cell marker expression was assessed by flow cytometry, cytokine production by ELISA, gene expression by RT-qPCR. Key findings Propolis alone maintained TLR-2, TLR-4, HLA-DR, CD40 and CD80 expression in the monocytes; however, its combination with either MAGE-1 or LPS decreased CD40 expression triggered by the stimuli. Propolis maintained RA action on cell marker expression. Propolis inhibited TNF-α (with either EtxB or MAGE-1) and IL-6 (with either RA or MAGE-1), and increased IL-10 (with MAGE-1) production. Propolis downmodulated LC3 expression induced by LPS. It also induced a lower NF-kB expression than control cells and its combination with RA induced a higher expression than the stimulus alone. Conclusions Propolis potentially affected innate immunity by downmodulating the monocytes pro-inflammatory activity.