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SummaryThe sensitivity of the passive hemagglutination reaction was increased considerably by repeated freezing and thawing of antigen-coated erythrocytes. Cells were stabilized by pyruvic aldehyde followed by formaldehyde and then coated with antigen at low pH. After the desired HA titer was attained, the cells were stored in liquid nitrogen. Antigen-coated cells stored at 20° gradually deteriorated during the course of 18 months.

SummaryThe sensitivity of the passive hemagglutination reaction was increased considerably by subjecting stabilized rabbit erythrocytes to periodate oxidation, repeated freezing and thawing, or to low pH prior to coating with the antigen BSA. Cells were stabilized by pyruvic aldehyde followed by formaldehyde and then coated with antigen at low pH.

Allogeneic antiserums against human lymphocytes were specifically inhibited by M protein from beta hemolytic group A Streptococcus pyogenes, type 1. Analogous M proteins from streptococcus types 3, 4, 5, 6, 12, and 14 had little or no inhibitory activity. The specific inhibition by M protein is not a result of anticomplementary activity or of coating of the lymphocyte surface. Streptococcal polysaccharide and 73 other polysaccharides were inactive. Because all seven HL-A specificities tested were inhibited, it is inferred that M1 protein has a structure common to human histocompatibility antigens.