Objective

Evaluate how and why intravenous gamma globulin (IVIg) affects IdeS-cleavage of IgG.

Introduction

IgG degrading enzyme of Streptococcus pyogenes (IdeS) cleaves human IgG in two steps, first cleaving one of the heavy chains resulting in a single-cleaved IgG (scIgG) and then cleaving the second heavy chain into a F(ab')₂ and an Fc-fragment. As IdeS is of bacterial origin, most people have been exposed to IdeS during their life-time, through common streptococcal infections, and as a consequence developed antibodies against IdeS. Thus, anti-IdeS antibodies are present in most individuals, and importantly, also in IVIg.

Method

A serum pool generated from 100 individuals (50 men and 50 women, IgG concentration 12 mg/mL) and human IVIg (Privigen, IgG concentration 10 mg/mL) were subjected to IdeS treatment in the presence or absence of different amounts of additional IVIg. IdeS treatment was performed for 2 h at 37[deg]C. Inactive IdeS was used as a decoy to block anti-IdeS antibodies in some experiments. Cleavage of IgG was analyzed by SDS-PAGE.

Results

IdeS treatment of the human serum pool showed that 3.8 [micro]g/mL of IdeS partially cleaved IgG into scIgG and that 7.5 [micro]g/mL IdeS fully cleaved IgG into F(ab')₂ and Fc-fragments. Lower concentrations of IdeS than 3.8 [micro]g/mL had no effect. IdeS treatment of human IVIg showed a pattern similar to the serum pool with partial cleavage at 1.9-3.8 [micro]g/mL IdeS and full cleavage at 7.5 [micro]g/mL. When increasing the amount of IVIg it was clear that higher concentrations of IVIg required higher IdeS-concentrations to accomplish the same effect on IgG.

By applying a decoy-approach (inactive IdeS addition) it was demonstrated that IVIg contains neutralizing anti-IdeS antibodies that explains the inhibitory effect seen when increasing the concentration of IgG (IVIg). When these neutralizing antibodies were blocked, IdeS generated scIgG at very low IdeS-concentrations (0.47 [micro]g/mL) and fully cleaved IgG as effectively as it cleaved the serum pool (at 7.5 [micro]g/mL). Furthermore, it was demonstrated that addition of IVIg to IdeS treated serum neutralized remaining IdeS-activity.

Conclusion

Based on the data presented it can be concluded that the concentration of IdeS required to cleave IgG in serum as well as IVIg depends on the amount of neutralizing anti-IdeS antibodies present. Furthermore, it was shown that a high dose of IVIg may serve as an antidote to IdeS.

CITATION INFORMATION: Runström A., Järnum S., Jordan S., Winstedt L., Kjellman C. Anti-IdeS Antibodies in IVIg and Its Effect on IdeS Activity Am J Transplant. 2017;17 (suppl 3).

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