Serum immunoglobulin G4 in Sjögren's syndrome: a pilot study

Immunoglobulin IgG4 plays a role in the pathogenesis of the Mikulicz disease previously considered a form of primary Sjögren's syndrome (pSS). We investigated serum levels of IgG4, total IgG, C3, and C4 serum complementary components in patients suspected of Sjögren's syndrome. Basic laboratory and immunological tests, including IgG4 and IgG concentration, were performed on 20 healthy and 68 suspected of pSS individuals. We distinguished: group I: 48 pSS patients; group II (sicca): 20 patients with dryness without pSS. We revealed: statistical differences between groups I and II concerning hypergammaglobulinemia, ESR, RF, ANA, Ro, and La antibodies; lower IgG4 levels and IgG4/IgG ratio in group I compared to healthy individuals (p < 0.0435; 0.0035, respectively); no significant differences in the concentrations of IgG4 and IgG4/IgG ratio between sicca and control groups. significantly lower (p < 0.0002) C4 levels in group I compared to other groups; significant differences in C4 concentration and IgG4/IgG ratio between three groups (p = 0.0002 and p = 0.0090, respectively); a weak negative correlation between C4 and IgG (r =- 0.274) in the whole database; weak positive correlation between C4 and IgG4/IgG ratio (r = 0.237); a negative correlation of IgG4, IgG4/Ig ratio and C4 with focus score (r = - 0.281; r = - 0.327; r = - 0.406, respectively). IgG4 serum levels were significantly decreased compared to healthy subjects. IgG4 and C4 levels correlated with infiltrations in minor salivary glands. Hypergammaglobulinemia and decreased serum C4 component levels are typical for pSS.