Staphylococcus aureus protein A antibody-mediated haemagglutination assay. A study on the interaction between protein...

A method has been described for the enhancement of the sensitivity of the passive haemagglutination (PHA) reaction through intact cells of Staphylococcus aureus (Cowan I) bearing protein A (SAPA) which bind Fc portion of IgG derived from many mammalian species. Interactions between Mycobacterium tuberculosis sonicate antigen-sensitized red cells and antimycobacterial antibodies derived from M. tuberculosis immunized goat, rabbit, guinea pig and mouse sera and sera from human tuberculosis patients have been used as model systems. SAPA cells were allowed to bind antibodies from sera and subsequently cross-react with antigen-sensitized red cells. Co-haemagglutination occurred only when specific antibodies were bound by SAPA cells. The sensitivity of this SAPA antibody-mediated haemagglutination assay (SAPA-AMHA) was found to be higher than that of PHA reaction and it depended upon protein A antibody affinity. The specificity of the interaction between SAPA cell-bound antibodies and red-cell-bound antigens suggests that these two reagents offer a simple and sensitive approach for the study of antigen-antibody reactions.