Streptolysin O inhibition by serum gamma G-globulin and beta-lipoprotein after blocking of nonesterified cholesterol by digitonin.

Abstract

Abstract Physicochemical blocking of serum nonesterified cholesterol by digitonin and removal of the uncombined digitonin by transdehydroandrosterone eliminate the cholesterol molecules accessible to streptolysin O. In the presence of digitonin, denatured or pathological β-lipoproteins lose their streptolysin-inhibiting activity while inhibition by pure γ-globulin is not affected. Twenty normal and 198 pathological sera with high titers were studied. After digitonin fixation, they show a drop in the inhibition titer often greater than the one after β-lipoprotein precipitation by dextran sulphate. The difference was statistically significant at P=0.05, and it is assumed that β-lipoprotein precipitation does not totally suppress the non-specific inhibition of streptolysin while the digitonin method does. In normal subjects and in 89 cases with streptococcal diseases, both methods gave average titers corresponding to 30 to 50 per cent of the preliminary titers; "specific" and serum titers were more or less parallel. On the contrary, the specific titers were low in patients with unexplained high titers. In these cases there was no correlation between specific and serum titers. Therefore, the classic Todd procedure for antistreptolysin (ASL) determination can be considered as valuable in streptococcal disease but uncertain in some other conditions. In 3 cases with extremely high serum inhibition capacity related to the gamma globulin (which was monoclonal in 2 cases), the digitonin treatment did not change the titers after removal of the β-lipoprotein. Cholesterol blocking prior to titration of streptolysin inhibition allows a very specific determination of antistreptolysin.