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The role of carbohydrate in the structure and function of nephritic factor
Insights
Nephritic factors (NeFs) from patients with proliferative lupus nephritis and membranoproliferative glomerulonephritis showed abnormal heavy and light chains. These structural abnormalities in NeFs are linked to their pathogenic activity.
Area of Science:
- Immunology
- Nephrology
- Protein Chemistry
Background:
- Nephritic factors (NeFs) are autoantibodies implicated in glomerular diseases like proliferative lupus nephritis (PLN) and membranoproliferative glomerulonephritis (MPGN).
- Understanding the structural basis of NeF activity is crucial for elucidating disease pathogenesis.
Purpose of the Study:
- To purify and characterize nephritic factors (NeFs) from patients with proliferative lupus nephritis (PLN) and/or membranoproliferative glomerulonephritis (MPGN).
- To investigate the structural abnormalities of NeFs and their correlation with pathogenic activity.
Main Methods:
- Purification of NeFs from IgG fractions using EA C43bBb elution.
- Analysis of heavy (H) and light (L) chain components using PAGE-SDS.
- Enzymatic (neuraminidase) and chemical (periodate oxidation, reduction, alkylation) treatments to assess structural integrity and activity.
Main Results:
- Six NeFs were purified, all exhibiting abnormal H chains with varying molecular weights (55,000–65,000 Da) compared to normal (53,500 Da).
- Two NeFs possessed enlarged L chains (26,500 Da vs. 23,500 Da).
- NeF activity and structural abnormalities were localized to the F(ab')2 and Fd fragments; carbohydrate moieties appeared essential for activity.
Conclusions:
- NeFs associated with PLN and MPGN exhibit distinct structural abnormalities in their H and L chains.
- These structural alterations, particularly involving H chains and potentially carbohydrate components, are critical for NeF pathogenic function.
Abstract:
Six nephritic factors (NeFs) were purified from the IgG fraction of sera of patients with PLD and/or MPGN by elution from EA C43bBb. All had at least one abnormal H chain component when examined by PAGE-SDS and two additionally had a large L chain. Four different H chains were found. Their apparent molecular weights and the frequency with which they occurred were: 65,000 (one NeF), 61,500 (four NeFs), 57,000 (two NeFs) and 55,000 (one NeF) compared with 53,500 daltons for normal H chain. The molecular weight of the large L chains was 26,500 daltons (cf. 23,500 for normal L chain). Both the NeF activity and the large components were located in the F(ab')2 fragment of the molecule and after reduction the large component was found in the Fd fragment of the H chain. Neuraminidase treatment of purified NeF caused a 1-2% decrease in apparent molecular weight of the large H chain on PAGE-SDS. Mild periodate oxidation, sufficient to cause primarily loss of carbohydrate, caused a marked loss of activity. Reduction and alkylation of NeF under neutral conditions caused only a small loss of activity but after acid dissociation the H and L chains were completely inactive.