Antibody to streptococcal zymogen in the serum of patients with acute glomerulonephritis: a multicentric study.
BACKGROUND
Cationic streptococcal proteinase (erythrotoxin B) and its precursor, zymogen, are putative nephritogenic antigens. The present study was designed to test whether serum titers to these antigens were good markers of streptococcal infection associated with glomerulonephritis.


METHODS
We studied 153 patients (male/female = 104/49, age range, 2 to 23 years old) with acute poststreptococcal glomerulonephritis (APSGN) from three countries (Venezuela, Chile and Argentina). The site of the initial infection was the skin in 84 patients, the throat in 55 patients and was unknown in 14 patients. In addition, we studied 23 patients (1 to 24 years old) with streptococcal infection not associated with glomerulonephritis (14 patients with impetigo and 9 patients with pharyngitis). As control group, 93 healthy individuals (54 males, 2 to 19 years old) were studied. Anti-zymogen and anti-proteinase titers were determined in a single laboratory by ELISA, and the intra- and interassay coefficients of variation were 5.3% and 8.5%, respectively. ASO titers and anti-DNAse B titers were also done.


RESULTS
Anti-zymogen titers of 1:800 to 1:3200 had likelihood ratios (sensitivity/1-specificity) for detection of streptococcal infection in APSGN patients ranging from 2.00 to 44.2 in Argentina, Chile and Venezuela. Anti-zymogen titers decreased one to two months after APSGN and they were 1 to 3 log2 dilutions higher that anti-proteinase titers. Receiver operating characteristic (ROC) curves showed that anti-zymogen titers were consistently superior to anti-streptolysin O and anti-DNAse B titers as markers for streptococcal infection in APSGN.


CONCLUSIONS
These results suggest that increased anti-zymogen antibody titers are the best available marker for streptococcal infection associated with acute glomerulonephritis.
Parra
G
G
Renal Service and Laboratory Hospital Universitario de Maracaibo, Venezuela.
Rodríguez-Iturbe
B
B
Batsford
S
S
Vogt
A
A
Mezzano
S
S
Olavarría
F
F
Exeni
R
R
Laso
M
M
Orta
N
N
D000208:Acute Disease; D000293:Adolescent; D000328:Adult; D000907:Antibodies, Bacterial / Q000097:blood*; D001426:Bacterial Proteins; D002648:Child; D002675:Child, Preschool; D003546:Cysteine Endopeptidases / Q000276:immunology*; D004792:Enzyme Precursors / Q000276:immunology*; D005098:Exotoxins / Q000276:immunology*; D005260:Female; D005921:Glomerulonephritis / Q000382:microbiology*; D006801:Humans; D007169:Impetigo / Q000382:microbiology; D008297:Male; D008565:Membrane Proteins; D012680:Sensitivity and Specificity; D013297:Streptococcus pyogenes / Q000276:immunology*
D000907:Antibodies, Bacterial; D001426:Bacterial Proteins; D004792:Enzyme Precursors; D005098:Exotoxins; D008565:Membrane Proteins; C117980:SpeA protein, Streptococcus pyogenes; C027951:erythrogenic toxin; D003546:Cysteine Endopeptidases