Adsorption of 3H-fatty acid esters of streptococcal groups A and E cell wall polysaccharide antigens by red blood cells and their effect on hemagglutination.

The streptococcal group A and E cell wall polysaccharide (PS) antigens were esterified under identical conditions with four fatty acid chlorides (lauroyl, myristoyl, palmitoyl, and stearoyl), varying from 12 to 18 carbon atoms. With group A PS, it was shown that the four resulting esters varied in their ability to sensitize red blood cells (RBC) to agglutination in the presence of specific antiserum. The most active was palmitoyl (16C) followed by myristoyl (14C). The least active was the lauroyl ester (12C). One-tenth as much palmitoyl ester was required as stearoyl group A PS ester. Such variation in the ability to sensitize RBC was not demonstrated with the group E esters, with the exception of the lauroyl ester which was the least active. Removal of N-acetylglucosamine from the esterified and the nonesterified group A PS by enzyme action resulted in a significant loss of serological activity of both antigens. No appreciable difference in the rate or total loss of activity was found in either case. It was demonstrated that both tritium-labeled stearic and palmitic acids and their respective PS esters were adsorbed in significant amounts to RBC. The results indicate that the esterified antigens were adsorbed to the RBC because of the presence of the fatty acid in the PS ester. Attempts to block the receptor sites on the red cell by presensitizing the cells with fatty acid were negative. Likewise, the adsorbed ester did not prevent the uptake of fatty acid at the levels tested. Tritium-labeled esterified group A PS and group E PS were used to show that the amount of antigen required to produce maximal agglutination was the same when cells from the same individual were used, whereas this was not the case when cells from different individuals were used. The amount of antigen required to produce maximal agglutination varied from one batch of sheep RBC to another. Once the optimal concentration of antigen was reached, any additional adsorption did not increase the titer of agglutination.