Quantitative character of fibrinogen uptake by M+ and M- variants of Streptococcus pyogenes.

Fibrinogen was labelled with 125Iodine by mild chemical oxidation and its binding to Streptococcus pyogenes was subjected to quantitative analysis, inhibition and desorption studies. Fibrinogen was bound both by virulent and avirulent (M protein-positive and M protein-negative) matched strains of several serotypes. In all pairs of strains fibrinogen uptake was much higher by the M-positive variants. The ratio of bound fibrinogen to total fibrinogen was highly dependent both on the concentration of fibrinogen and the concentration of cocci. Equilibrium binding studies showed that the binding was a multifactorial process. Probably not only receptor fibrinogen interactions but also interactions between bound and unbound fibrinogen molecules took place. The uptake of fibrinogen was highly depressed in avirulent strains and practically uninfluenced in virulent strains by the presence of albumin or immunoglobulin. The bond between fibrinogen and streptococci is therefore different in virulent and avirulent variants. The fibrinogen receptors on the cell surface are specific.