Determination of antibody to pneumococcal polysaccharides with chromic chloride-treated human red blood cells and indirect hemagglutination.

A method is described for the quantitation of serum antibody to type-specific pneumococcal polysaccharide. The method uses highly purified pneumococcal polysaccharide coated onto human O+ red blood cells by the chromic chloride technique. Each of 14 pneumococcal polysaccharide types was individually coated onto red blood cells and used to determine the antibody response following primary immunization. The method was found to be sensitive, detecting antibody titer increases of several hundred to a thousand-fold. The presence of high preimmunization antibody titers did not obscure the detection of antibody titer increases. The method detected antibody of both the immunoglobulin M and immunoglobulin G class when quantitated after ultracentrifugation and sucrose density gradient separation. By using serum samples obtained from volunteers immunized with a single pneumococcal polysaccharide, the method was standardized resulting in an ability to compare samples taken at different times and obtained from different sources. The method appears to be simple, reproducible, and inexpensive and can be utilized to determine the antibody response following immunization in large population studies.