Abstract
BACKGROUND: Royal jelly (RJ) has traditionally been used to maintain health, and its fatty acids (10-hydroxy decanoic acid and 10-hydroxy-2-decenoic acid) are reported to have immunomodulatory effects. We recently developed fermented RJ (fRJ) by fermenting RJ with honeybee queen (Apis mellifera)-derived lactic acid bacterium, Lactobacillus panisapium M1. fRJ increased the 10-hydroxy decanoic acid content five-fold and facilitated macrophage phagocytosis. In this study, we explored the components involved in the fRJ-induced enhancement of macrophage phagocytosis and assessed the biological mechanisms of these components. METHODS: The effects of fRJ on the phagocytosis of negatively charged carboxylate-modified latex beads, zymosan, IgG-coated beads, and apoptotic cells, Toll-like receptor 2 (TLR2) and phagocytic receptor expression, and p38, c-Jun N-terminal kinase (JNK), and extracellular signal-regulated kinase (ERK) phosphorylation were assessed in the murine macrophage cell line J774.1. To explore the mechanisms of fRJ-induced macrophage phagocytosis, we used TLR2, mitogen-activated protein kinases (MAPKs), cluster of differentiation 36 (CD36), scavenger receptor inhibitors, and small interfering RNA. Phagocytosis was assessed using fluorescence microscopy or flow cytometry, whereas mRNA, protein, and cell surface antigen expression was assessed using quantitative polymerase chain reaction, western blotting, and flow cytometry, respectively. RESULTS: fRJ enhanced macrophage phagocytosis of carboxylate-modified latex beads and apoptotic cells. Additionally, L. panisapium M1 enhanced macrophage phagocytosis. Moreover, the assessment of lactic acid bacteria-mediated signaling pathways revealed that fRJ enhanced TLR2 expression, promoted p38 and JNK phosphorylation, and facilitated activator protein-1 nuclear translocation. However, fRJ-induced macrophage phagocytosis was reduced by the presence of inhibitors targeting TLR2, p38, and JNK. fRJ facilitated the gene expression of scavenger receptors, including Msr1 and Cd36, and this upregulation was suppressed by TLR2 inhibition. Surprisingly, fRJ-induced augmentation of macrophage phagocytosis was not suppressed by CD36 inhibition. However, it was significantly attenuated by the broad-spectrum scavenger receptor inhibitor polyinosinic acid. CONCLUSIONS: The results indicate that fRJ enhances macrophage phagocytosis through TLR2/MAPK/SR, and L. panisapium M1 primarily contributes to immune function.