Studies on the measurement of antibody against an extracellular protein associated with nephritogenic streptococci by using the enzyme-linked immunosorbent assay (ELISA)

Using the enzyme-linked immunosorbent assay technique, the antibody to a purified nephritis-strain associated protein (NSAP) of group A streptococcus, type 12 (A 374 strain) isolated from a patient with acute post-streptococcal glomerulonephritis (APSGN) was measured in the sera obtained from patients with APSGN and Impetigo without APSGN. In addition, the sera from patients with acute rheumatic fever (ARF), scarlet fever (SF) and normal individuals were also tested. The NSAP utilized in the studies was purified by preparative SDS-PAGE from the concentrated culture supernatant fluid of group A streptococcal strain (A 374). The results obtained were as follows : 1) The NSAP was assayed for its purity by analytical SDS-PAGE and double gel diffusion test. SDS-PAGE pattern of the NSAP showed only a single protein band which corresponded to a mol. wt. of 46, 000 daltons and the serum of patient with APSGN gave a line with the NSAP of A 374 strain. 2) The ELISA test was performed using the antigen (NSAP) concentration of 5μg/ml and 1 : 4, 000 or 1 : 8, 000 dilution fluid of the patients' sera. There were no differences in antibody titers against the NSAP between the ARF and normal groups or the SF group and normal group of children. Antibody. titers, however, to the NSAP were significantly higher in the sera of patients with APSGN and Impetigo without APSGN than in the sera of normal individuals. Furthermore, when antibody titers against the NSAP in the sera of patients with APSGN were compared with those in the sera of Impetigo the titers of the former sera were significantly higher than those of the latter sera (p