Biomedical subjects

Jonathan Barratt

Publications and source records attributed to Jonathan Barratt.

5 recordsLinked to original sources

PubMed2006

O-glycosylation of serum IgA1 antibodies against mucosal and systemic antigens in IgA nephropathy.

In IgA nephropathy (IgAN), serum IgA1 with abnormal O-glycosylation deposits in the glomerular mesangium. The underlying mechanism of this IgA1 O-glycosylation abnormality is poorly understood, but recent evidence argues against a generic defect in B cell glycosyltransferases, suggesting that only a subpopulation of IgA1-committed B cells are affected. For investigation of whether the site of antigen encounter influences IgA1 O-glycosylation, the O-glycosylation of serum IgA1 antibodies against a systemic antigen, tetanus toxoid (TT), and a mucosal antigen, Helicobacter pylori (HP), was studied in patients with IgAN and control subjects. Serum IgA1 was purified from cohorts of patients with IgAN and control subjects with HP infection and after systemic TT immunization. The IgA1 samples were applied to HP- and TT-coated immunoplates to immobilize specific antibodies, and IgA1 O-glycosylation profiles were assessed by binding of the O-glycan-specific lectin Vicia villosa using a modified ELISA technique. Although total serum IgA1 had raised lectin binding in IgAN, the O-glycosylation of the specific IgA1 antibodies to TT and HP did not differ between patients and control subjects. In both groups, IgA1 anti-HP had higher lectin binding than IgA1 anti-TT. This study demonstrates that IgA1 O-glycosylation normally varies in different immune responses and that patients produce the full spectrum of IgA1 O-glycoforms. IgA1 with high lectin binding was produced in response to mucosal HP infection in all subjects. The raised circulating level of this type of IgA1 in IgAN is likely to be a consequence of abnormal systemic responses to mucosally encountered antigens rather than a fundamental defect in B cell O-glycosylation pathways.

Adult↗

PubMed2006

O-glycosylation of serum IgD in IgA nephropathy.

In IgA nephropathy (IgAN), serum IgA1 with abnormal O-glycosylation preferentially deposits in the glomerular mesangium. The control of O-glycosylation is poorly understood. Among Ig isotypes, only IgD, produced early in B cell development, and IgA1, produced by mature B cells, are O-glycosylated. For investigation of the stage of B cell maturation at which the defect seen in IgAN arises, the O-glycosylation of serum IgA1 and IgD was studied in IgAN and controls. Serum was obtained from 20 patients with IgAN and 20 control subjects. The O-glycosylation profiles of native and desialylated IgA1 and IgD were measured in an ELISA-type system using the lectins Helix aspersa and peanut agglutinin, which bind to alternative forms of O-glycan moieties. The lectin-binding patterns of the two immunoglobulins differed in all participants, with that of IgD suggesting that it is more heavily galactosylated than IgA1. Defective O-glycosylation of IgA1, probably taking the form of reduced galactosylation, was confirmed in IgAN in this study. This undergalactosylation was not shared by IgD; in contrast, IgD carried more galactosylated O-glycans in IgAN than controls. The contrasting lectin-binding patterns of IgA1 and IgD shows that Ig O-glycosylation is differentially controlled during B cell maturation. Compared with controls, O-glycosylation in IgAN is incomplete in IgA1 but more complete in IgD. These observations show that abnormal IgA1 O-glycosylation in IgAN is not due to an inherent defect in glycosylation mechanisms but arises only at a later stage in B cell development and may be secondary to aberrant immunoregulation.

Adult↗

PubMed2005

IgA nephropathy.

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Glomerulonephritis, IGA↗

PubMed2004

Pathogenesis of IgA nephropathy.

In IgA nephropathy (IgAN), there is dysregulation of the IgA response to a wide range of antigens. The dysregulation promotes synthesis of polymeric IgA1 (pIgA1) with physicochemical characteristics that favor mesangial deposition, including altered O-glycosylation of the hinge region. This may be the synthesis of IgA in the systemic compartment, which has the phenotype of mucosal IgA. There is not a change in IgA1 structure to an entirely abnormal form; rather, there is a shift that results in a proportional increase in forms of IgA1 also found in healthy individuals. Altered O-glycosylation could favor pIgA1 deposition by promoting formation of macromolecular IgA and immune complexes. Mesangial injury follows through interactions of pIgA1 with the cells and extracellular matrix proteins of the mesangium and the activation of complement. The final clinical expression of IgAN also depends on generic factors, including hypertension and proteinuria, and a fibrotic renal response. No single "IgAN gene" has been identified, and it is likely that multiple interacting genes will eventually prove to underlie susceptibility to IgAN and the risk of progressive renal disease. These new pathogenic insights have not yet led to new therapeutic opportunities.

Animals↗

PubMed2004

Inhibitors directed towards caspase-1 and -3 are less effective than pan caspase inhibition in preventing renal proximal tubular cell apoptosis.

BACKGROUND: Uncontrolled apoptosis contributes to tubular cell deletion in renal scarring. Caspase-3 has a central role in the execution of apoptosis and may provide a target for regulating cell death. Here we evaluate three caspase inhibitors: B-D-FMK (pan caspase inhibitor), Z-DEVDFMK (predominantly Caspase-3 inhibitor) and Z-VAD-FMK (predominantly Caspase-1 and -3 inhibitor) to ameliorate apoptosis induced by cisplatin in rat proximal tubular (RPT) cells. METHODS: Caspase-3 activity (substrate cleavage assay) and protein (immunocytochemistry and Western blotting), apoptosis (Annexin V flow cytometry, in situend labelling of fragmented DNA, light/electron microscopy and DNA laddering) and cell survival (trypan blue exclusion and propidium iodide flow cytometry) were determined in RPT cells exposed to cisplatin with and without caspase inhibitors. RESULTS: Cisplatin induced a dose-dependent increase in Caspase-3 activity and 8-fold of increase in apoptosis (p < 0.01) when applied for 24 h at 100 microM. B-D-FMK (40 microM), Z-DEVD-FMK (15 microM) and Z-VAD-FMK (22 microM) almost completely inhibited the 25-fold increase in Caspase-3 activity and decreased apoptosis from 15.9 +/- 4.4 to 2.0 +/- 0.6% (p < 0.01), 15.0 +/- 2.2 and 15.0 +/- 2.2% respectively. DNA ladders were visible in cisplatin-treated cells, which disappeared following addition of B-D-FMK and decreased with Z-VAD-FMK and Z-DEVD-FMK. Cisplatin reduced cell survival to 61% by trypan blue exclusion. B-D-FMK and Z-VAD-FMK increased this to 87 and 75%, but Z-DEVD-FMK had no significant effect. CONCLUSIONS: Cisplatin causes an increase in RPT apoptosis that is associated with increased Caspase-3 activity. All caspase inhibitors were equally effective at reducing Caspase-3 activity, however the pan caspase inhibitor B-D-FMK was more effective at preventing apoptosis and increasing cell survival. Therefore, pan caspase inhibition offers the greatest potential for the prevention of renal tubular cell deletion by uncontrolled apoptosis.

Amino Acid Chloromethyl Ketones↗