Erythrocyte complement C3b receptor (CR1) levels and immune complex-induced manifestations in patients with primary Sjögren's syndrome.

To assess the importance of low C3b receptor (CR1) numbers on erythrocytes for the development of clinical features in patients with primary Sjögren's syndrome (SS), two groups of patients were selected for investigation--one without (n = 13), and one with (n = 21) extraglandular, possibly immune complex-induced, clinical manifestations during the disease course. A preponderance (p less than 0.01) of low CR1 levels was found in patients with primary SS (mean 57%) as compared with normal controls (mean 70%), but the CR1 levels did not differ between the two groups of patients. The CR1 values did not correlate with the levels of circulating immune complexes and C3d. Although the preponderance of low CR1 levels is pathogenetically intriguing, it appears to be of little help in the clinical assessment of patients with primary SS.