GROUP-A STREPTOCOCCUS-LIPOSOME ELISA ANTIBODY-TITERS TO GROUP-A POLYSACCHARIDE AND OPSONOPHAGOCYTIC CAPABILITIES OF THE ANTIBODIES

Antibodies reactive with group A streptococci (GAS) carbohydrate were studied by ELISA and in an indirect bactericidal assay. The ELISA used GAS carbohydrate covalently bound to phosphatidylethanolamine incorpo rated into liposomes so that both precipitating and nonprecipitating a ntibodies were measured. Sera from children from different geographic areas exhibited marked differences in levels of anti-GAS carbohydrate antibody, which increased with age. The antibodies were predominantly of IgG. In bactericidal assays, most of these sera promoted phagocytos is of several type-specific M-positive strains. Opsonization was also related to serum levels of anti-GAS carbohydrate antibodies. These ops onizing antibodies were depleted from the serum by absorption of the s era on an N-acetyl-D-glucosamine affinity column. Antibody eluted from this column could partially restore opsonization of GAS. Anti-GAS car bohydrate antibodies play a major role in these opsonophagocytosis ass ays.