Characterization of an antibody directed against a surface component of normal and pleomorphic cells of Streptococcus sanguis.

Whole cells of Streptococcus sanguis were utilized as an immunoadsorbent to purify large quantities of an antibody (S1) directed against a cell surface component. The S-1 antibody was isolated from antisera to normal (N) and pleomorphic (O) cells by a similar adsorption-elution procedure. The S-1 antibody isolated from antisera to N cells reacted in gel diffusion in identify with the S-1 antibody to O cells, indicating that the antigen which binds S-1 antibody (Ag-1) may not be radically altered when cells become pleomorphic. The S-1 antibodies directed against both N and O cells had restricted heterogeneity, indicating that for both types of cell Ag-1 may have a simple repeating structure. However, N cells were agglutinated to a greater extent by S-1 antibody than O cells. In addition the distribution of the bound S-1 antibody became altered as the cells became pleomorphic. Utilizing the technique of indirect immunofluorescence we observed that the S-1 antibody was distributed evenly on the surface of N cells. As the cells became pleomorphic, the antibody appeared to bind preferentially at the cell poles (capping). Later, as the cells became more grossly deformed, additional bands of immunofluorescence appeared to bisect the cells. Electron microscopic analysis indicated that the bound antibody was not associated with septal notches. The results suggest that the arrangement rather than the immunological properties of Ag-1 became altered as cells became pleomorphic.