Abstract: Objective To investigate the role of natural killer-22 (NK-22) cells in the synovial fluid in the proliferation of
fibroblast-like synoviocytes (FLS) in patients with rheumatoid arthritis (RA) and explore the possible signal pathway involved.
Methods NK-22 cells in the SF of RA patients were sorted by flow cytometry. NK-22 cells were cultured for two weeks and the
purity was detected by flow cytometry before stimulation with 20 ng/ml phorbol 12-myristate 13-acetate and 0.5 μmol/L
ionomycin for 4 h. The level of interleukin-22 (IL-22) in the culture medium supernatant was then measured with ELISA. The
proliferation of FLS in the presence of the culture supernatant of NK-22 cells was assessed with MTT assay at 24, 48 and 72 h,
and the effect of IL-22 antibody on FLS proliferation was also observed. Real-time PCR and Western blotting were used to
detect Stat3 mRNA and p-Stat3 protein levels, respectively, in the FLS exposed to rhIL-22 and AG490. Results NK-22 cells were
successfully sorted by flow cytometry with a purity exceeding 90%. The levels of IL-22 in the supernatant of NKp44+NK cell
culture averaged 1273.42±254.48 pg/ml. The FLS proliferated rapidly 24, 48, and 72 h after the addition of culture supernatant
of NK-22 cells (P<0.05). IL-22 antibody obviously inhibited the proliferation of FLS induced by NK-22 cell culture supernatant
(P<0.05). Exposure of the FLS to rhIL-22 obviously increased cellular Stat3 expression levels, which were significantly lowered
by the addition of AG490 (P<0.05). Conclusion NK-22 cells in the SF of RA patients can produce high concentrations of IL-22 to
promote the proliferation of FLS through the STAT3 signal pathway.