STUDIES ON THE BINDING BETWEEN STREPTOCOCCAL M PROTEIN AND ANTIBODY

Abstract

A streptococcal antigen was prepared which was soluble in 40% saturated ammonium sulfate (SAS) but became precipitable in 40% SAS when bound to specific antibody globulin. An acid extract of type 12 streptococci was labelled with I131 and most of the non-type specific antigen removed by precipitation with 40% SAS in the presence of heterologous antiserum directed against 6 other types of streptococci. This partially purified supernatant (l*M12) was approximately 10% insoluble in 40% SAS in the presence of normal rabbit serum, 60% insoluble in the presence of homologous-type 12 antiserum, and 20% insoluble in the presence of hyperimmune heterologous-type antiserum. An increased precipitation of I*M12 was still observed when the homologous-type 12 antiserum was diluted as much as 17000, whereas the effect was absent when the heterologous-type antiserum was diluted 1:270. In addition to measuring the I M12 binding capacity of a given antiserum, diversity of antisera directed against type 12 streptococci could be demonstrated by means of I*M12-antibody dissociation curves and the effect of antigen dilution on binding capacity. It was shown that antibody present early during immunization was more readily dissociated from I M12 than was antibody present later in the course of immunization.