Background/Purpose: Rheumatoid arthritis (RA) is an autoimmune disease characterized by the presence of autoantibodies and autoreactive T cells, leading to synovitis and joint destruction. The TNF-family members OX40 and OX40L are crucial for the generation of memory T cells, which can lead to persistence of immunity, but also autoreactivity. Both molecules exist in soluble isoforms and sOX40 has been suggested to be antagonistic to the membrane bound isoform.  Signals through the OX40 receptor leads to AKT phosphorylation, thereby leading to increase of anti-apoptotic signals and maintenance of the memory response, while signals through the OX40L are mediated by ERK, which upregulates survival signals in a similar manner. Objectives of the study was to investigate the bioactivity and levels of OX40 and OX40L in RA

Methods: Paired PBMCs and SFMCs from 12 RA patients were compared with PBMCs from 6 healthy volunteers (HV). Cells were stained with anti-OX40 and anti-OX40L and the cell markers CD4 and CD45RO and analysed by flow cytometry. To determine the activation pathways, cells were stimulated with sOX40 and sOX40L in a time dependent setup, followed by intracellular staining with anti-AKT and anti-ERK antibody. Phosphorylation status were analysed by phosphoflow.

Results: In the blood, increased expression of OX40 observed by memory T cells (CD4+CD45RO+) from RA patients (11.7% (5.8%-13.30%)) compared with HV (4.9% (2.8%-6.0%)), p<0.05. Furthermore, OX40+ memory T cells accumulated in the SF of RA patients (17.0% (11.6%-30.3%) p<0.01). B cells from SFMC expressed significantly more OX40L (11.8% (3.2%-25.5%)) compared with the PBMCs (2.8% (0.8%-4-8%)) from RA patients and from HV (2.4% (1.6%-3.1%)) (All p<0.05).The unstimulated CD4+ T cells from SFMCs and PBMCs from RA patients had significantly elevated AKT phosphorylation compared with PBMCs from HV (p<0.01). When stimulated with CD3 alone, the CD4+ T cells from RA patients had increased AKT phosphorylation, whereas the CD4+ T cells from HV had decreased phosphorylation. When stimulated with CD3 and sOX40L together, cells from HV more than doubled their AKT phosphorylation, while the increase in AKT phosphorylation was very modest in RA patients; however, the MFI remained elevated in RA patients through all time points. The ERK phosphorylation of RA B cells was not increased upon sOX40 stimulation, indicating that bi-directional signaling in RA B cells is absent.

Conclusion: Cells expressing OX40 and OX40L accumulate in the inflamed joints of RA patients. This supports an on-going local activity of the adaptive memory responses in RA. Further, CD4+ T cells from RA patients have significantly higher AKT phosphorylation compared with HV, and thus, have up regulated anti-apoptotic signals. The absence of B cell response after sOX40 stimulation could support the antagonistic effects of this molecule.

ACR Meeting Abstracts - https://acrabstracts.org/abstract/ox40-t-cells-and-ox40l-b-cells-accumulate-in-the-inflamed-joints-and-ox40-signalling-is-skewed-towards-autoreactivity/