The Immune-inflammatory Characteristics of Primary Sjögren's Syndrome with Different Levels of Rheumatoid Factors

Background Rheumatoid factor (RF) is a common autoantibody found in patients with primary Sjögren's syndrome (pSS), but its specific role in the disease is not fully understood. Objective To explore the immune-inflammatory characteristics of pSS patients with different levels of RF. Methods This study included 262 pSS patients who visited the Department of Rheumatology of Traditional Chinese Medicine at China-Japan Friendship Hospital from December 2018 to September 2022. Patients were divided into three groups based on RF levels: negative group (RF<20 U/mL, n=137), low-titer positive group (RF: 20-60 U/mL, n=47), and high-titer positive group (RF>60 U/mL, n=78). Clinical data, including general information, clinical manifestations, symptom scores, and haematological indexes, were collected and compared among groups. Results The RF positivity rate in 262 pSS patients was 47.7% (125/262), including 14 males (5.3%) and 248 females (94.7%), with a median age of 57.0 (49.0, 63.0) years, an average age of onset of (48.7±11.6) years, and a median disease duration of 60.0 (24.0, 120.0) months. There were no significant differences in gender, age, age of onset, or disease duration among the three groups (P>0.05). The top three common clinical manifestations in pSS patients were dry mouth (257 cases), dry eyes (247 cases), and fatigue (235 cases). The incidence of haematological involvement and arthritis was higher in the high-titer positive group than in the negative group (P<0.05). With the increase in RF titer, the incidence of haematological involvement (χ2trend=6.992, Ptrend=0.008) and arthritis (χ2trend=10.918, Ptrend=0.001) showed an upward trend. As RF titer increased, the proportions of pSS patients with antinuclear antibody≥1∶160 (χ2trend=40.691, Ptrend<0.001), anti-SSA antibody positivity (χ2trend=26.138, Ptrend<0.001), anti-Ro52 antibody positivity (χ2trend=31.426, Ptrend<0.001), anti-SSB antibody positivity (χ2trend=23.682, Ptrend<0.001), elevated erythrocyte sedimentation rate (χ2trend=40.132, Ptrend<0.001), elevated immunoglobulin (Ig) A (χ2trend=7.508, Ptrend=0.006), elevated IgG (χ2trend=71.570, Ptrend<0.001), decreased complement 3 (χ2trend=7.452, Ptrend=0.006), decreased neutrophil count (χ2trend=8.364, Ptrend=0.004), and decreased hemoglobin (χ2trend=6.390, Ptrend=0.011) all showed an upward trend. Conclusion With the increase in RF titer, the proportion of pSS patients with serum immunological abnormalities and extra-glandular involvement increases. High RF titers have predictive value for arthritis and hematologic involvement.