Serum CXCL4 Increase in Primary Sjögren's Syndrome Characterizes Patients with Microvascular Involvement and Reduced Salivary Gland Infiltration and Lymph Node Involvement

CXCL4 is an antiangiogenic and immunomodulatory chemokine. We aimed to investigate serum levels of CXCL4 in primary Sjögren's syndrome (pSS), looking for associations with disease features. Thirty-nine consecutive pSS patients underwent clinical-serological assessment and nailfold videocapillaroscopy (NVC). Thirty-six patients and 30 controls affected by osteoarthritis were also investigated for serum levels of CXCL4 and soluble E-selectin (sE-selectin). CXCL4 was higher in pSS patients than in controls (1.79 [0.2-11.18] vs 1.023 ng/ml [0.02-14.45], p < 0.05), particularly in those without anti-La/SSB antibodies (2.89 [1.01-11.18] vs 1.69 ng/ml [0.2-2.72], p < 0.05), while it was lower in pSS patients with a focus score ≥1 at lip biopsy (1.44 [0.86-2.1] vs 2.24 ng/ml [1.64-3.25], p < 0.05) and clinically evident lymphadenopathy (1.53 [0.38-1.7] vs 2.08 ng/ml [1.45-3.03], p < 0.05). CXCL4 correlated with disease duration (r = 0.35, p < 0.05) and sE-selectin (r = 0.45, p < 0.01). Patients with Raynaud's phenomenon (RP) had more frequently abnormal CXCL4 levels than patients without RP (11/15 vs 3/21, p < 0.001), enlarged capillaries (14/16 vs 7/23, p < 0.001) and capillary loss at NVC (14/16 vs 6/23, p < 0.001). The hitherto unknown association of increased serum CXCL4 with features of microvascular impairment in pSS, along with the negative association with features of lymphocytic response (i.e., the absence of subset disease-specific autoantibodies, a low focus score, and the absence of lymphadenopathy) suggest clarifying the possible implication of this chemokine in pSS pathogenesis in larger studies.