Immunological studies of post-streptococcal sequelae: serological studies with an extracellular protein associated with nephritogenic streptococci.

Using the Ouchterlony double diffusion and the crossed-immunoelectrophoresis techniques the reactivity to a purified extracellular product of nephritogenic group A streptococci (NASP) was examined with both acute and convalescent sera obtained from patients with documented post-streptococcal glomerulonephritis and patients with documented acute rheumatic fever. The streptococcal antigen utilized in these studies was first purified on SDS gels and then eluted from the gel, resulting in a single protein band on SDS electrophoresis. Double diffusion studies revealed that only nephritis patients reacted to this extracellular product associated with nephritogenic strains, whereas rheumatic fever sera produced no line of precipitation. An assay of serial bleedings from nephritis patients suggested that the antibody reactive to the NASP was in higher titre in the acute phase of the disease and decreased with convalescence. In confirmation of these findings, crossed-immunoelectrophoresis experiments were conducted with a battery of sera from acute nephritic and non-nephritic patients against the NASP antigen. A striking increase was detected in the reactivity of nephritis patients (96%) compared to non-nephritis sera (15-20%). Comparison between acute and convalescent sera using this technique confirmed the finding of decreasing antibody titre with resolution of disease. These findings of a specific humoral response in patients with acute post-streptococcal nephritis to the NASP of nephritogenic strains further implicates an aetiological function to this protein.