Exploring the role of TNF/TNFR superfamily and NF-?B pathway in regulating B7/CD28 expression in rheumatoid arthritis: An in-vitro study

Background: The TNF/TNFR superfamily and B7/CD28 costimulatory molecules are critical regulators of immune responses; however, their interplay in rheumatoid arthritis (RA) remains unclear. Objectives: To investigate whether the TNF/TNFR superfamily regulates B7/CD28 expression via the NF-?B pathway in RA and to evaluate its effects on synovial cell inflammation and apoptosis. Methods: Peripheral blood mononuclear cells (PBMCs) and fibroblast-like synoviocytes (FLS) were obtained from 40 patients with active rheumatoid arthritis (RA) (13 males, 27 females; mean age 42.3 ± 8.1 years, range 26-55; DAS28-ESR > 3.2) and 40 age- and sex-matched healthy controls (15 males, 25 females; mean age 41.8 ± 7.9 years, range 26-54) with no history of arthritis or autoimmune diseases; all participants provided written informed consent. A co-culture system of PBMCs and FLS was established and divided into three groups: control (healthy PBMCs + FLS), model (RA PBMCs + FLS) and inhibition (RA PBMCs + FLS treated with PDTC, an NF-?B inhibitor). After 48 hours, cell viability, apoptosis, inflammatory cytokines (TNF-?, IL-1?), COX-2, Bax, Bcl-2, TNF-R1/TNF-R2 mRNA and the expression of CD28 and CD80 on CD4+ and CD8+ T cells were assessed. Results: Compared to controls, the model group exhibited increased FLS viability, reduced apoptosis, elevated levels of TNF-?, IL-1?, COX-2, Bcl-2 and TNF-R1/R2 mRNA, along with decreased Bax expression and lower CD28/CD80 expression on CD4+ T cells (all P < 0.05). NF-?B inhibition with PDTC significantly reduced FLS viability and increased apoptosis, downregulated IL-1? and COX-2 and restored CD28/CD80 expression on CD4+ T cells (P < 0.05), but did not alter TNF-? or TNFR mRNA levels. Conclusion: Inhibition of the NF-?B pathway attenuates RA-FLS inflammation and restores B7/CD28 expression on T cells; however, these effects were not directly mediated by changes in TNF/TNFR expression.