Preferentially immunoglobulin (IgG) subclasses production in primary Sjögren's syndrome patients

Background: Patients with primary Sjögren's syndrome (pSS) mostly have high levels of polyclonal immunoglobulin (IgG) and selective increase of IgG subclasses. As IgG subclasses profiles represent specific immunological processes and may be indicative of the underlying pathological pattern in pSS, it would be of great clinical importance to investigate the distribution of IgG subclasses in pSS patients. Methods: In archived sera from 155 patients with pSS, 50 patients with systemic lupus erythematosus (SLE) and 50 normal controls were analyzed by immunonephelometric assay. Results: The median levels of IgG1, IgG2, IgG3 and IgG4 in pSS patients were 11300 mg/L, 6130 mg/L, 961 mg/L and 142 mg/L, respectively. When compared with the normal controls, significant increases of IgG1 (p<0.001), IgG2 (p<0.001) and IgG3 (p<0.001) was observed in pSS patients, while the IgG4 level was significantly decreased (p=0.002). The ratio of IgG1/IgG2 in pSS patients was 2.3±1.4, which was significantly higher than that in the normal controls (p<0.001). When the pSS patients were divided into different groups, a higher level of IgG3 was observed in pSS with systematic disorders (p=0.008). In addition, the level of IgG1 was statistically higher in the anti-Ro or anti-La positive group than that in the negative group (p<0.001), but the IgG4 concentration was lower than that in the negative group (p=0.046). A significant positive correlation between the concentration of IgG3 and the disease duration (p<0.001) was also identified. Conclusions: The data supported the pathogenic role of IgG1 and IgG3 subclasses in the process of pSS. Further investigations to elucidate the reasons for the increase of IgG2 and whether IgG2 has any contribution to the pathogenesis of pSS are needed.