AB0080 IMBALANCE OF MONOCYTE/MACROPHAGE POLARIZATION IN PERIPHERAL BLOOD AND SYNOVIAL FLUID OF RHEUMATOID ARTHRITIS PATIENTS

Background

Macrophages strongly contribute to the pathogenesis of rheumatoid arthritis (RA), initiating the inflammatory response, the join damage, but also may promote the resolution of inflammation and the restoration of tissue immune-homeostasis [1,2]. This seems to be related to an unbalanced immunological response mediated by macrophages through their polarization into "classically" and "alternatively" activated phenotypes (M1 or M2) [3,4]. However, little is known about the M1 and M2 phenotype of their circulating precursors (monocytes) in the peripheral blood (PB) and the synovial fluid (SF) of RA patients.

Objectives

To characterise the polarization status (M1 and M2) of PB and SF monocytes of RA patients together with their distribution in the monocyte subsets by flow cytometry (FC).

Methods

Nineteen RA patients not yet treated with biological DMARDs (mean age 62±14 years), who fulfilled the 2010 ACR/EULAR classification criteria for RA and treated in accordance with EULAR recommendation, as well as 19 age-matched healthy subjects (HSs) were enrolled after signed informed consent. PB and SF cells were collected from each RA patient, whereas only PB cells were collected from HSs. The expression of CD14 and CD16 surface markers allowed to identify the monocyte population and the monocyte subsets: "classical"(CD14++CD16-), "intermediate"(CD14++CD16+), and "non-classical"(CD14-CD16+). The M1 phenotype (M1 monocytes) was identified by the evaluation of CD80, CD86, TLR2 and TLR4, whereas the M2 phenotype (M2 monocytes) was identified evaluating CD204, CD163 and CD206 surface markers. Results were expressed as percentage of positive cells over total leukocytes from PB and SF. Statistical analysis was carried out by Mann-Whitney non-parametric test.

Results

In RA patients, the percentage of CD14++CD16+monocytes was significantly higher in PB compared to that in HS (p<0.001), and it was higher in SF compared to PB (p<0.05). The percentage of CD14-CD16+monocytes was significantly increased in RA-PB compared to HS-PB and RA-SF (p<0.01; p<0.05). RA patients were characterized by an increased percentage of M1 monocytes (CD80⁺CD86⁺TLR2⁺TLR4⁺CD204^-CD163^-CD206^-cells) in PB compared to HSs and compared to RA-SF. The percentage of M2 monocytes (CD204⁺CD163⁺CD206⁺CD80^-CD86^-TLR2^-TLR4^-cells) was also increased in RA-PB compared to HS-PB and to RA-SF, but this increase was lower and not significant than that observed for M1 monocytes. Moreover, the M1-M2 monocyte ratio was 8:1in RA-PB. Therefore, in RA patients, circulating M1 monocytes belonged to the "non-classical" subset, whereas M2 monocytes belonged to the "classical" subset. The percentage of circulating mixed M1/M2 monocytes (CD80⁺CD86⁺TLR2⁺TLR4⁺CD204⁺CD163⁺CD206⁺cells) was higher in RA patients compared to HSs. Moreover, in RA patients, the percentage of these cells was higher in SF than in PB and they primarily belonged to the "intermediate" monocyte subset. Interestingly, the highest percentage of M2 and mixed M1/M2 monocytes was observed in PB and SF of RA patients receiving a higher daily (25mg) and cumulative glucocorticoid dosages.

Conclusion

The results confirm that RA is an immune-inflammatory disease mainly mediated by both M1 monocytes and macrophages, as demonstrated by the increase in the percentage of circulating M1 monocytes. Glucocorticoids might contribute to the M1 to M2 transition, which characterizes RA patients under remission by increasing mixed M1/M2 and M2 monocyte percentage.

References

[1]Okabe Y et al. Nat Immunol. 2016;17:9–17. [2]Kurowska-Stolarska M, et al. Nat Rev Rheumatol. 2022;18:384-97. [3]Cutolo M, et al. Front Immunol. 2022;13:867260. [4]Ross EA, et al. Front Immunol. 2021;12:708186.

Acknowledgements:

NIL.

Disclosure of Interests

Stefano Soldano: None declared, Emanuele Gotelli: None declared, Paola Montagna: None declared, Rosanna Campitiello: None declared, Alberto Sulli: None declared, Vanessa Smith: None declared, Maurizio Cutolo Grant/research support from: BMS, Boehringer, Amgen.