Properties of circulating IgA molecules in Henoch-Schönlein purpura nephritis with focus on neutrophil cytoplasmic antigen IgA binding (IgA-ANCA): new insight into a debated issue. Italian Group of Renal Immunopathology Collaborative Study on Henoch-Schönlein purpura in adults and in children.
BACKGROUND
The presence and the pathogenetic role of circulating IgA reacting with neutrophil cytoplasmic antigens (IgA-ANCA) in patients with Henoch-Schönlein purpura (HSP) is still debated. This study was aimed to investigate some characteristics of serum IgA and macromolecular IgA in HSP patients, focusing on IgA-ANCA.


METHODS
Eighty-seven HSP patients with biopsy proved renal involvement (51 adults and 36 children) enrolled in a multicentre study of the Italian Group of Immunopathology were investigated.


RESULTS
Significantly high levels of IgA immune complexes were found in both adults (P < 0.05) and children (P < 0.01), while the binding of IgA to jacalin, was significantly low in children with HSP (P < 0.01) only. Two series of ELISA were done for IgA-ANCA, in two different laboratories. Increased binding to PMN crude extracts (P < 0.01) without any modification in IgA binding to proteinase 3 was found by either specific ELISA. Conversely, the binding of IgA to myeloperoxidase (MPO) was found to be significantly (P < 0.05) increased with positive values in 25% of patients by one assay only. Three of four sera with positive IgA-MPO ANCA exhibited binding in Western-blot studies with the MPO preparation used in ELISA to a 28-kDa species. D-galactose and N-acetyl-glucosamine decreased the binding of serum IgA to MPO more in HSP than in controls (P < 0.05).


CONCLUSIONS
The conflicting reports on IgA-ANCA may reflect some atypical characteristics of the reaction which can be detected only by some ELISAs. We suggest that not an antigen-antibody reaction but a lectinic interaction due to abnormal composition of IgA carbohydrate side chains may account for the IgA-ANCA reaction in patients with HSP nephritis.
Coppo
R
R
Nephrology and Dialysis Department, Regina Margherita Children's Hospital, Torino, Italy.
Cirina
P
P
Amore
A
A
Sinico
R A
RA
Radice
A
A
Rollino
C
C
D000328:Adult; D019268:Antibodies, Antineutrophil Cytoplasmic / Q000378:metabolism*; D015153:Blotting, Western; D002648:Child; D004797:Enzyme-Linked Immunosorbent Assay; D006801:Humans; D011695:IgA Vasculitis / Q000276:immunology*; D007070:Immunoglobulin A / Q000097:blood / Q000378:metabolism*; D009393:Nephritis / Q000276:immunology*; D009195:Peroxidase / Q000378:metabolism
D019268:Antibodies, Antineutrophil Cytoplasmic; D007070:Immunoglobulin A; D009195:Peroxidase