Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.5.1.52 (PNGase F)
 1,527 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Expression, saturation, and endocytosis of IgA Fc receptors (Fc alpha R) were analyzed in blood phagocytic cells of patients with alcoholic liver cirrhosis (ALC). Surface Fc alpha R expression was decreased in monocytes but not in neutrophils, as evaluated by IgA binding and anti-Fc alpha R mAb. The Fc alpha R of ALC patients were saturated by IgA1 and IgA2. ALC Fc alpha R had a higher M(r) (60 to 90 kDa) than those of controls (55 to 75 kDa) with a similar 32-kDa protein core after N-glycanase treatment, suggesting the expression of Fc alpha R molecules with altered carbohydrate moieties. Treatment of U937 cells with IFN-gamma induced a decrease of surface Fc alpha R expression in a dose-dependent manner, with a similar M(r) as observed for ALC patient Fc alpha R (60 to 90 kDa). Fc alpha R endocytosis was induced by anti-Fc alpha R or IgA. Neutrophils internalized Fc alpha R molecules faster than did monocytes. Endocytosed Fc alpha R co-localized with cathepsin D, suggesting an endolysosomal compartment pathway. In ALC monocytes, Fc alpha R endocytosis was defective, with nearly 50 to 60% of receptors detected on the cell surface even after 90 min at 37 degrees C. Similarly, delayed Fc alpha R endocytosis was observed on IFN-gamma-treated U937 cells as compared with PMA-activated cells. Defective internalization of surface-bound IgA with reflux of IgA to cell surface was also observed on ALC monocytes, but not on normal cells preincubated with patients' plasma, ruling out direct effects of IgA. The inverse correlation between monocyte Fc alpha R levels and serum IgA levels associated with defective endocytosis suggest that altered Fc alpha R expression might contribute to receptor saturation and generation of increased plasma levels of IgA and IgA-immune complexes in ALC patients.
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PMID:Altered expression of monocyte IgA Fc receptors is associated with defective endocytosis in patients with alcoholic cirrhosis. Potential role for IFN-gamma. 763 20

In contrast to antigen-antibody complexes containing native human IgA, solid-phase-deposited IgA activates the alternative complement pathway and binds C3b. To investigate the role of carbohydrate chains in this, various human IgA preparations were treated with neuraminidase alone or together with N-glycanase or O-glycanase, or with mixed glycosidases from the oral bacterium, Streptococcus mitis. Depletion of oligosaccharides was determined by carbohydrate analysis. Removal of sialic acid and N-linked glycan chains greatly increased the C3b-fixing properties of normal serum IgA1 and IgA2. Myeloma IgA1 and IgA2 proteins and secretory IgA had higher C3b-binding activity than normal serum IgA, and this was further increased by removal of sialic acid and N-linked glycans. Fc alpha and Fc alpha-SC fragments of myeloma and secretory IgA1, respectively, but not Fab alpha fragments, obtained by cleavage with bacterial IgA1 proteases and also free secretory component, fixed C3b by the alternative pathway.
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PMID:The role of the carbohydrate chains in complement (C3) fixation by solid-phase-bound human IgA. 792 4