Type 17-specific immune pathways are active in early spondyloarthritis

Area of Science:

• Immunology
• Rheumatology

Background:

• Undifferentiated, early inflammatory arthritis (EIA) can evolve into seropositive or seronegative rheumatoid arthritis (RA), peripheral spondyloarthritis (SpA), or remain as seronegative undifferentiated inflammatory arthritis (UIA).
• Immune pathways in early SpA and seronegative UIA are less understood compared to seropositive RA.

Purpose of the Study:

• To investigate the immune pathways active in synovial CD4+ and CD8+ T cells within EIA patients.
• To differentiate immune profiles in early stages of various inflammatory arthritis subtypes.

Main Methods:

• Synovial fluid (SF) samples from 30 EIA patients were analyzed.
• Expression of IL-17A, IFNγ, and TNFα in CD8+ and CD4+ T cells was quantified using flow cytometry.
• Final diagnoses were confirmed by independent clinicians blinded to the study data.

Main Results:

• Significant enrichment of IL-17A+CD8+ T cells (Tc17) was observed in patients who later developed SpA compared to those diagnosed with seronegative UIA.
• Patients diagnosed with seropositive RA showed low Tc17 cell frequencies, consistent with established disease findings.
• CD8+IFNγ+ T cells were significantly higher in RA SF compared to SpA or seronegative UIA SF.

Conclusions:

• Adaptive T cell cytokine pathways vary in early disease stages among RA, SpA, and seronegative UIA.
• Early SpA is characterized by the activation of Tc17 cell pathways.
• These findings highlight distinct immunological signatures in the early phases of inflammatory arthritis.