Absorption of human alpha 2-macroglobulin with selected strains of streptococci

A new interaction was observed between human alpha 2-macroglobulin (alpha 2M) and selected strains of streptococci. The streptococci bound alpha 2M. After its elution from the bacteria, alpha 2M was demonstrated by immunoelectrophoresis against anti-human alpha 2M. The binding of alpha 2M to one streptococcal strain of serological group C and two of group G was confirmed by radial immunodiffusion. Treating the streptococci with trypsin reduced their reactivity with alpha 2M. On the other hand, prolonged treatment with 6 M guanidine-HCl had no effect on the alpha 2M binding. Binding sites for alpha 2M were most likely protein structures on the streptococcal surface.