Nephritogenic antigen for acute poststreptococcal glomerulonephritis.

To the Editor: We read with surprise the recent paper by Batsford et al.1 on the nephritogenic antigen for acute poststreptococcal glomerulonephritis. The authors' data regarding glomerular deposition and serum antibody response to nephritis-associated plasmin receptor (NAPlr) or streptococcal glyceraldehyde-3-phosphate dehydrogenase in acute poststreptococcal glomerulonephritis patients were completely different from ours.2, 3 We detected serum anti-NAPlr antibody at high titer in 92% (46/50) of acute poststreptococcal glomerulonephritis patients, and positive glomerular staining was observed in 100% (25/25) of patients in the early stage by direct immunofluorescence staining with rabbit anti-NAPlr antibody.3 We also showed that distribution of NAPlr deposition and plasmin activity were identical.4 Discrepancy in histologic staining results is easily explained by methodology. Batsford et al.1 used the indirect immunofluorescence staining with the different antibody that they made, whereas we used direct immunofluorescence staining for NAPlr because nonspecific staining increases and specific staining is difficult to assess by indirect methods. We suspect the discrepancy in serum reactivity against glyceraldehyde-3-phosphate dehydrogenase detected by ELISA was mainly because of the use of different antigens. The antigens differed in size (37–39 kDa (theirs) vs 43 kDa (ours)). We suspect the existence of two distinct isoforms of glyceraldehyde-3-phosphate dehydrogenase that would show differential migration by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and different immunologic reactivity. Different isolation procedures may preferentially extract different isoforms, thereby causing the difference in results.