Binding of aggregated human beta2-microglobulin to surface protein structure in group A, C, and G streptococci.

A novel mammalian-microbial "short circuit" has been demonstrated between aggregated human beta2-microglobulin and group A, C, and G streptococci. Bacteria belonging to nine gram-positive and three gram-negative species were tested for binding of radiolabeled beta2-microglobulin. All 10 individual strains of group A streptococci showed a high degree of reactivity with aggregated human beta2-microglobulin. Among 27 group C and 28 group G streptococci, 9 and 6 strains, respectively, were highly reactive, whereas the remaining strains showed a lower, but definite level of beta2-microglobulin binding. Of 11 group B streptococci, 4 were slightly positive. All strains among the other eight species were completely negative. Simultaneous testing of A, C, and G streptococci for immunoglobulin binding showed a lack of correlation between type II and III Fc reactivity and beta2-microglobulin binding. There was no inhibition of uptake of aggregated beta2-microglobulin to reactive strains when excess amounts of human immunoglobulin were added. The beta2-microglobulin-binding surface structure was found to be markedly sensitive to trypsin digestion. The relative trypsin resistance of the immunoglobulin-binding protein in the digestion experiments further demonstrated the dissociation between these two reactivities.