In Vitro Binding ANTI‐GM 1 IGM To GM 1 Inhibition Pattern By Three Intravenous γ‐Globulin Preparations In Patients With Distal Lower Motor Neuron Syndrome

Aim of the study: To evaluate the in vitro inhibition of different Intravenous γ‐Globulin (IVIgG) preparations and of their F(ab′) 2 fragments on the anti‐GM 1 IgM binding to GM 1 . Methods: Amounts of three commercially available IVIgG preparations (Sandoglobulin, Ig Vena and Flebogamma) were digested by 10 mg/mL pepsin acetate buffer. Dialyzed digests were gel filtrated by a Sephadex G‐150 column and PBS to obtain purified F(ab′) 2 fragments. Two patients with a distal lower motor neuron syndrome (A.B., female with motor conduction blocks at the electrophysiological examination; P.M., male without motor conduction blocks) with high anti‐GM 1 IgM titer (1:84,000 and 1:52,000) were studied. Serum amounts of these patients were mixed with increasing amounts (from 0.25 to 5 times IgG patient molar concentration) of the three IVIgG preparations or their gel filtrated F(ab′) 2 fragments, or with 2% bovine serum albumin. One hundred μL of each mixture was incubated in microtiter wells coated with 500 ng/mL GM 1 methanol solution. Peroxidase conjugated goat anti‐human IgM and O‐phenylenediamine solutions were added according to the ELISA procedure and anti‐GM 1 IgM titer was calculated by absorbance at 490 nm, extrapolating the value from a standard curve. Each mixture percent of inhibition of anti‐GM 1 IgM to GM 1 was expressed as a ratio between the difference of anti‐GM 1 titer before and after IVIgG or F(ab′) 2 incubation and the baseline anti‐GM 1 titer. Results: Intact IVIgGs were able to inhibit binding of anti‐GM 1 IgM to GM 1 in a quite dose‐dependent manner, but at a different extent either between patients than among different IVIgG preparations: in patient A.B. the inhibition ranged from 8% to 71% using Sandoglobulin, 2% to 54% using Ig Vena and 9% to 65% using Flebogamma, while in patient P.M. the inhibition ranged respectively 0% to 35%, 3% to 62% and 8% to 74%. Similar results were reached using F(ab′) 2 fragments: in patient A.B. the inhibition ranged respectively from 7% to 76%, 5% to 68% and 8% to 59%, while in patient P.M. the inhibition ranged respectively from 1% to 40%, 5% to 59% and 10% to 81%. Conclusions: IVIgG preparations inhibit the in‐vitro binding of anti‐GM 1 IgM to GM 1 supplying a possible explanation of IVIgG therapy in‐vivo efficacy. This inhibition is due to F(ab′) 2 fragments and probably involves an idiotypic ‐ anti‐idiotypic interaction, because the same IVIgG or F(ab′) 2 preparations give different percent inhibition of anti‐GM 1 to GM 1 binding according to the treated patient anti‐GM 1 idiotopic pattern.