Neutrophil infiltration into the early RA synovial tissue is associated with disease activity and early remission

Aims: Neutrophils drive local pathology of rheumatoid arthritis (RA) in the synovial tissue (ST) through production inflammatory mediators, cytokines, and extracellular traps. Yet despite these established roles, the clinical relevance of their infiltration into the tissue with regards to disease initiation and progression remains poorly understood. This project therefore sought to assess the relationship between neutrophil infiltration into the early RA ST and clinical outcomes.

Methods: Arthroscopic ST samples preserved in FFPE from n = 26 patients with treatment-naïve RA (<12 months of onset, fulfilling 2010 ACR/EULAR criteria) were stained with H&E. Polymorphonuclear cells were judged by morphology by two independent observers. Five field of views (20x) from each section were manually assessed for neutrophil infiltration using the following scoring system: 0 = none observed; 1 = 1–5 observed; 2 = 6–10 observed; 3 = 11–20 observed; 4 = >20 observed. The scoring method was validated by immunohistochemistry. For further validation of manual counts, matched bulk RNA sequencing data from the ST of the same patients were deconvoluted using CIBERSORT, and neutrophil fractions determined.

Results: Neutrophil infiltration as measured by CIBERSORT was moderately positively correlated with DAS28ESR and DAS28CRP (r = 0.3869, p = 0.0347, and r = 0.4503, p = 0.0125, respectively). Manual scores provided similar results, with a higher positive correlation of higher significance (r = 0.6029, p = 0.0011 with DAS28ESR, and r = 0.6601, p = 0.0002 with DAS28CRP). No association between either score was observed with disease duration or CCP or RF status. Patients who reached early remission (DAS28CRP < 2.4 at 3 months) had lower manual neutrophil infiltration scores at baseline than those who did not (p = 0.0267).

Conclusions: RA ST neutrophil content prior to treatment initiation was positively associated with disease activity; patients who achieved early remission had lower neutrophil counts at baseline. Together, these outcomes suggest that ST neutrophil content may prove useful as a predictive measure of disease activity and outcome, and targeting these cells may have future therapeutic utility.