Binding of aggregated human serum albumin to M12 and some other types of group A streptococci.

In radiobinding tests many group A, C and G streptococci react with IgG and IgA, irrespective of the antigen-combining sites, as well as with various other serum proteins, e.g. human serum albumin (HSA). The present study demonstrated that glutaraldehyde-aggregated, radiolabelled HSA (aHSA), in comparison to monomeric HSA, binds more avidly to streptococci. Of group A streptococci, strains representing types M6, M12, M18, M46, M55 and M57 displayed pronounced binding of aHSA whereas a number of other serotypes were non-reactive. The streptococcal sites involved proved to be relatively heat-resistant and highly sensitive to trypsin treatment. Human fibrinogen counteracted the binding of aHSA. The uptake by M12 was inhibited strongly by rabbit antiserum raised against M12, whereas other antisera were less active. The results suggest that the bacterial structure binding aHSA is a protein and that, in at least one serotype, M12, the binding occurs to the M-protein.