Abstract
BackgroundSynovial infiltration of monocytes is commonly associated with inflammation in rheumatoid arthritis (RA). Toll-like receptors (TLRs) are innate sensors that recognize cell debris and microbial components in host, a process contributing to maintain chronic inflammation in RA. We assessed the expression levels of TLR2 and TLR9 in monocyte subsets of active RA patients and characterized their cytokine profiles in response to synthetic and viral TLR2 and TLR9 agonists, including Epstein-Barr virus (EBV) which is suspected to contribute to RA symptoms.MethodsPrevalence of monocyte subsets CD14++ CD16−, CD14+ CD16+ and CD14low CD16++ was evaluated in blood and synovial fluids of active RA patients and levels of TLR2 and TLR9 in monocyte subsets were measured by flow cytometry. Enriched monocytes derived from RA patients and healthy donors were stimulated in vitro with synthetic TLR2 and TLR9 agonists and with EBV particles or viral DNA. Intracellular cytokine profiles were determined in respective monocyte subsets. Finally, the presence of EBV genome was evaluated by real-time PCR in blood and synovial monocytes of RA patients.ResultsNumbers of CD14+ CD16+ and CD14low CD16++ were found to increase in blood of RA patients compared to healthy controls, while all three subsets were detected in synovial fluids. TLR2 is abundantly expressed on blood and synovial CD14++ CD16− and CD14+ CD16+ monocytes from RA patients. Levels of TLR9 were increased on all three subsets of blood monocytes but markedly enhanced in monocytes isolated from synovial fluids. Compared to healthy controls, CD14++ CD16− monocytes of RA patients displayed an enlarged capacity to produce proinflammatory cytokines after stimulation with synthetic TLR2 and TLR9 agonists while both CD14++ CD16− and CD14+ CD16+ monocytes showed increased response to EBV stimulation. The presence of EBV genome was also detected in monocytes and neutrophils of a significant proportion of patients.ConclusionPatients with active RA show an increased expression of TLR2 and TLR9 on monocyte subsets and display higher production of inflammatory cytokines in response to TLR agonists. The presence of EBV genome in monocytes and neutrophils reinforces the suspected role of the virus in the exacerbation of RA symptoms.
Highlights
Synovial infiltration of monocytes is commonly associated with inflammation in rheumatoid arthritis (RA)
CD14+ CD16+ and CD14low CD16++ monocyte levels are increased in blood from patients with active RA Three distinct monocyte subsets are defined in humans, two of them expressing the CD16 marker
We have first determined by flow cytometry the proportion of these three monocyte subsets in blood of patients with active RA compared to healthy volunteers
Summary
Synovial infiltration of monocytes is commonly associated with inflammation in rheumatoid arthritis (RA). We assessed the expression levels of TLR2 and TLR9 in monocyte subsets of active RA patients and characterized their cytokine profiles in response to synthetic and viral TLR2 and TLR9 agonists, including Epstein-Barr virus (EBV) which is suspected to contribute to RA symptoms. RA is characterized by synovial hyperplasia and inflammation resulting from a massive infiltration of inflammatory cells, including monocytes and neutrophils [1]. These cells play a key role in the progression of RA through the production of proinflammatory cytokines, leading to the development of an inflammatory environment and immune cell recruitment in the joints. In RA patients, the frequency of monocytes expressing CD16 antigen (independently of the level of expression of CD16) was found to be increased in blood and synovial fluids [10, 11]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
