Synovial Fluid-Derived Exosomes from Osteoarthritis Patients Modulate Cell Surface Phenotypes of Monocytes and Cytokine Secretions

BACKGROUND: Exosomes can be found in the synovial fluid of inflamed knee joints, which play a significant role in osteoarthritis (OA) progression. However, their role - in modulating the cellular environment within the body, particularly monocytes remain unexplored. This study aimed to evaluate the immunomodulatory effect of exosomes on monocytes.

METHODS: Exosomes were isolated by ultracentrifugation and characterized using nanoparticle tracking analysis (NTA), scanning electron microscopy (SEM), and Western blot. The effect of exosomes in modulating monocyte phenotypes as well as cytokine secretion were further assessed in a co-culture condition using flow cytometry and ELISA accordingly.

RESULTS: Exosomes were identified as spherical particles with a size distribution ranging from 30 nm to 150 nm. These nanoparticles intensely expressed exosome protein markers including CD9, CD63, CD81, and HSP70. The expression of HLA-DR, CD14, and CD11b on monocytes decreased in the presence of exosomes after 24 h of incubation, regardless of the dose. Exosomes significantly induced the release of anti-inflammatory cytokines IL-1Ra in a time- and dose-dependent manner, while TNF-α secretion remains unchanged regardless of the presence or absence of exosomes.

CONCLUSION: This study highlights the immunoregulatory role of exosomes on monocytes, emphasizing the need for further studies into the underlying mechanism.