Some properties of cross reacting antibody of the ABO blood group system.

I N A PREVIOUS communication we have described applications of the mixed agglutination reaction to studies of the behavior of low-concentration minor cell components of mixed populations of ervthrocytes.’.2 This reaction is well suited to investigation of the behavior of isoagglutinins of the ABO group system since antigen-antibody reactions within this group system may be readily detected when the antigenically specific cell is diluted in “inert” cells to concentrations of the order of 1 part in 500 or less. At this concentration reactions between an isoagglutinin and a specific minor population ervthrocyte may l)e carried out without giving rise to agglutination of the sensitized cell. One of the problems chosen for study by the mixed agglutination technic was the (lefirntion of the so-called “cross reacting antibody” which is found 111 the serum of certain group 0 individuals. This antibody was originally detected by i loss: through the observation that absorption of a group 0 serum with group A cells removed not only a proportion of the anti-A isoagglutinin but also some of the anti-B activity of the serum. It was further sho vn that absorption of a group 0 serum vith group B cells resulted in a reduction of its anti-A titer as well as the expected reduction of anti-B titer. Demonstration of the power of sonic group 0 serums to cross react with group A and B cells was also made by Koeckert,4 who showed that some anti-B activity was Present in diiates lTIa(le froin group A cells which had been exposed to group 0 serum and, also, that anti-A activity could be found in eluates from group B cells treate(l with group 0 serum. The clinical importance of cross reacting antibody has l)een clearly (lemonstrateci liv Rosenfield, who found it to he consistently resent in the serum of group 0 mothers ‘hose infants suffered from ervthroblastosis clue to ABO inccmpatihility. Attempts to provide an adequate theoretical explanation of the cross reacting property of group 0 serum has k’(l to the estal)lisbment of two schools of thought. These are summarized as follows : ( 1 ) That there exists in certain group 0 serums an antibodymolecule with the combined specificity “anti-A