Neutrophil-released enzymes can influence composition of circulating immune complexes in multiple sclerosis.

During NET formation, the content of neutrophils granules is released into the intercellular milieu. Consisting of many proteases and ROS species, formed NETs were shown to degrade cytokines (Schauer, Nat Med, 2014); while the content of neutrophil's azurophilic granules proved to contain glycosidases, secreted upon activation (Thaysen-Andersen, JBC, 2015), and formation of autoantibodies to neutrophil beta-glucoronidase was connected with the level of anti-MPO antibodies (Ab) (Martensson, Autoimmunity, 1992). Taking into account these facts, we aimed to investigate the possibility of NET-related changes in glycan composition on circulating IgG molecules and IgG-IgM immune complexes in multiple sclerosis (MS). This autoimmune disorder still has no reliable detection markers or established ways of treatment, besides widely accepted interferon therapy, making it a particularly interesting clinical condition. By applying capture lectin-ELISA, we analysed binding of α2,6 sialyl-specific lectins SNA, PSqL, and core α1,6-fucose specific lectin AAL to circulating IgG and related complexes in five groups of MS patients: untreated (17 persons); undergoing therapy with interferon (IFN) ß-1 b (15 persons), corticosteroids (methylprednisolone) (12 persons) and anti-B-cell monoclonal Ab (12 persons: Ocrelizumab, 6 persons and alemtuzumab, 6 persons). A group of 23 healthy donors served as control. Significant increase in neutrophil elastase activity, observed in the group of patients under corticosteroid treatment was also accompanied by sialyl-specific PSqL and SNA lectin binding to captured IgG molecules. Subsequent analysis demonstrated that sialic acid residues were exposed on free IgG and on circulating IgG-IgM immune complexes. Increased lectin binding was not observed for anti-myelin basic protein (one of the major autoAb in MS) Ab compared to total serum Ab. IFN therapy was accompanied by low neutrophil elastase activity and low amount of circulating immune complexes. Incubation of in vitro generated NETs with human serum revealed the digestion of high-molecular weight immune complexes with subsequent exposure of hidden glycoepitops. Obtained data indicate the potential of neutrophil-derived proteases to modify (partially degrade) circulating immune complexes leading to exposure of internal glycoepitops.

Glycosylation of random IgG distinguishes seropositive and seronegative rheumatoid arthritis.

The N-glycosylation of human immunoglobulins, especially IgGs, plays a critical role in determining affinity of IgGs towards their effector (pro- and anti-inflammatory) receptors. However, it is still not clear whether altered glycosylation is involved in only antibody-dependent disorders like seropositive rheumatoid arthritis (RA) or also in pathologies with similar clinical manifestations, but no specific autoantibodies like seronegative RA. The clarification of that uncertainty was the aim of the current study. Another study aim was the detection of specific glycan forms responsible for altered exposure of native glycoepitopes. We studied sera from seropositive RA (n = 15) and seronegative RA (n = 12) patients for exposure of glycans in native IgG molecules, followed by determination of specific glycans by capillary electrophoresis with laser-induced fluorescent detection (CE-LIF). Aged-matched groups of normal healthy donors (NHD) and samples of intravenous immunoglobulin IgG preparations (IVIG) served as controls. There was significantly stronger binding of Lens culinaris agglutinin (LCA) and Aleuria aurantia lectin (AAL) lectins towards IgG from seropositive RA compared to seronegative RA or NHD. CE-LIF analysis revealed statistically significant increases in bisecting glycans FA2BG2 (p = .006) and FABG2S1 (p = .005) seropositive RA, accompanied by decrease of bisecting monogalactosylated glycan FA2(6)G1 (p = .074) and non-bisecting monosialylated glycan FA2(3)G1S1 (p = .055). The results suggest that seropositive RA is distinct from seronegative RA in terms of IgG glycan moieties, attributable to specific immunoglobulin molecules present in seropositive disease. These glycans were determined to be bisecting GlcNAc-bearing forms FA2BG2 and FABG2S1, and their appearance increased the availability of LCA and AAL lectin-binding sites in native IgG glycoepitopes.