Recent Advances in Research Regarding Autoantibodies in Connective Tissue Diseases and Related Disorders

Omega-3 fatty acid intake suppresses induction of diverse autoantibody repertoire by crystalline silica in lupus-prone mice

Inhalation of crystalline silica (cSiO2) in the workplace is etiologically linked to lupus and other autoimmune diseases. Exposing lupus-prone NZBWF1 mice to respirable cSiO2 unleashes a vicious cycle of inflammation and cell death in the lung that triggers interferon-regulated gene expression, ectopic lymphoid structure (ELS) development, elevation of local and systemic autoantibodies (AAbs), and glomerulonephritis. However, cSiO2-induced inflammation and onset of autoimmunity can be prevented by inclusion of the ω-3 polyunsaturated fatty acid docosahexaenoic acid (DHA) into the diet of these mice. Since cSiO2 both causes cell death and interferes with efferocytosis, secondary necrosis of residual cell corpses might provide a rich and varied autoantigen (AAg) source in the lung. While it is known that the particle induces anti-nuclear and anti-dsDNA AAbs in NZBWF1 mice, the full extent of the cSiO2-induced AAb response relative to specificity and isotype is not yet understood. The purpose of this study was to test the hypotheses that cSiO2 exposure induces a wide spectrum of AAbs in the pulmonary and systemic compartments, and that dietary DHA intervention prevents these changes. Archived tissue fluid samples were obtained from a prior study in which NZBWF1 mice were fed purified isocaloric diets containing no DHA (control) or DHA corresponding calorically to human doses of 2 and 5 g/day. Mice were intranasally instilled with 1 mg cSiO2 or saline vehicle weekly for 4 weeks, then groups euthanized 1, 5, 9, or 13 weeks post-instillation (PI) of the last cSiO2 dose. Bronchoalveolar lavage fluid (BALF) and plasma from each time point were subjected to AAb profiling using a microarray containing 122 AAgs. cSiO2 triggered robust IgG and IgM AAb responses against lupus-associated AAgs, including DNA, histones, ribonucleoprotein, Smith antigen, Ro/SSA, La/SSB, and complement as early as 1 week PI in BALF and 5 weeks PI in plasma, peaking at 9 and 13 weeks PI, respectively. Importantly, cSiO2 also induced AAbs to AAgs associated with rheumatoid arthritis (collagen II, fibrinogen IV, fibrinogen S, fibronectin, and vimentin), Sjögren's syndrome (α-fodrin), systemic sclerosis (topoisomerase I), vasculitis (MPO and PR3), myositis (Mi-2, TIF1-γ, MDA5), autoimmune hepatitis (LC-1), and celiac disease (TTG). cSiO2 elicited comparable but more modest IgA AAb responses in BALF and plasma. cSiO2-induced AAb production was strongly associated with time dependent inflammatory/autoimmune gene expression, ELS development, and glomerulonephritis. AAb responses were dose-dependently suppressed by DHA supplementation and negatively correlated with the ω-3 index, an erythrocyte biomarker of ω-3 content in tissue phospholipids. Taken together, these findings suggest that cSiO2 exposure elicits a diverse multi-isotype repertoire of AAbs, many of which have been reported in individuals with lupus and other autoimmune diseases. Furthermore, induction of this broad AAb spectrum could be impeded by increasing ω-3 tissue content via dietary DHA supplementation.

Increased expression of caspase 1 during active phase of connective tissue disease

Key factors of pyroptosis play an important role in the inflammatory response to connective tissue disease (CTD). However, information on active and stable stages of CTD is scarce. To distinguish the differences of concentrations of C-reactive protein (CRP), caspase 1, caspase 4, caspase 5 and sCD14 in plasma between the patients with active and stable stages of CTD. A cohort study was conducted to recruit patients diagnosed with CTD of active phase and stable phase as well as health control. These data included the analysis of the concentration of sCD14, caspase 1, caspase 4 and caspase 5 in peripheral plasma by ELISA. The Wilcoxon rank-sum test was used to compare the two groups. The sex ratio and ages of the three groups were not different statistically. The concentrations of sCD14, caspase4 and caspase5 of plasma in the CTD of active phase and the stable phase as well as the health control. The concentration of caspase 1 in active phase of CTD (470.19 [422.33–513.14] pmol/L) was significantly higher than that in stable group (203.95 [160.94–236.12] pmol/L) and healthy control (201.65 [191.11–240.35] pmol/L] pmol/L) (p < 0.001, both), but there was no significant difference between stable group and healthy control (p = 0.2312). Similarly, the concentration of CRP in the active phase of CTD (8.96 [3.06–20.28] mg/L) was significantly higher than that in the stable group (3.00 [1.30–11.40] mg/L) and the healthy control (3.70 [2.30–4.73] mg/L) (p = 0.0013, p = 0.0006, respectively), but there was no significant difference between the stable group and the healthy control (p = 0.3205). However, there were no significant differences in the concentration of sCD14, caspase 4 and caspase 5 in the active phase of CTD and the stable group as well as the health group. Consequently, the patients of the active phase of CTD showed increased expression of caspase 1.