Neutralization of staphylococcal exotoxins in vitro by human-origin intravenous immunoglobulin

Human-origin intravenous immunoglobulin (IVIG) collected from healthy individuals was tested for its neutralizing activity against the hemolysin, toxic shock syndrome toxin-1 (TSST-1), and enterotoxins, produced by laboratory strains of methicillin-resistant Staphylococcus aureus (MRSA). The hemolytic activity of the culture supernatant against sheep red blood cells was reduced from 100% to 5.5% relative hemolysis in the presence of 0.156 mg protein/ml of IVIG. The maximum dilution endpoint of the culture supernatant for TSST-1-mediated latex aggregation was 32-fold. This level of TSST-1 activity was reduced to eightfold dilution by 0.78 mg protein/ml of IVIG, and the latex aggregation activity of undiluted TSST-1 in the culture supernatant was inhibited by 1.56 mg protein/ml of IVIG. Similarly, the enterotoxin A-mediated latex aggregation titer appeared to be a 320-fold dilution. This toxin activity was reduced to an 80-fold dilution and below a tenfold dilution by 0.049 through 0.78 and 1.56 mg protein/ml, respectively, of IVIG. These results show that IVIG has powerful neutralizing activity against hemolysin, TSST-1, and enterotoxin A. Therefore, IVIG may be useful for passive immunization therapy in patients suffering from diseases caused by MRSA exotoxins.