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The beneficial effect of intravenous immunoglobulin (IVIg) therapy in patients with autoimmune diseases is at least partially dependent on the content in IVIg of antibodies capable of interacting with variable regions (idiotypes) of autoantibodies. In the present study, we have evaluated the antibody activity to a panel of self and environmental antigens of IVIg preparations and their dimer-enriched fractions. Dimers were either obtained by affinity chromatography of IVIg on Sepharose-bound F(ab′)2fragments of IVIg or by size exclusion gel filtration chromatography of IVIg. Enrichment of IVIg in dimers was found to be associated with an increase in the antibody activity against self-antigens as compared with unchromatographed IVIg. Our findings extend previous observations on enhanced autoantibody content of the affinity chromatography-separated ‘connected’ fraction of IVIg and suggest that therapeutic preparations of IVIg enriched in dimers may be obtained by size exclusion chromatography. Separation by size increases the feasibility of industrial-scale preparation of IVIg with high dimer content that are endowed with high potential immunomodulatory activityin vivo.

The present study demonstrates that normal human immunoglobulins for therapeutic use (IVIg) contain anti-idiotypes that recognize an antigen-binding site-related idiotope of anti-Factor VIII autoantibodies defined by a mouse monoclonal antibody (MoAb). MoAb 20F2 was obtained by immunizing a mouse with affinity-purified anti-Factor VIII F(ab′) 2 fragments prepared from the IgG fraction of a patient with anti-Factor VIII autoantibodies. The monoclonal antibody was directed against an overlapping epitope on the antigen-binding site of the patient's anti-Factor VIII autoantibodies and the CH1 domain of human IgG1. The anti-Factor VIII activity of the patients' autoantibodies was neutralized by MoAb 20F2 in a dose-dependent manner. A fraction of the patient's anti-Factor VIII autoantibodies was specifically retained on affinity columns of Sepharosebound MoAb 20F2; anti-Factor VIII activity of antibodies in this fraction was totally inhibited by MoAb 20F2, indicating an idiotopic homogeneity of retained anti-Factor VIII autoantibodies. IVIg inhibited the anti-Factor VIII activity of 20F2 idiotope-positive F(ab′) 2 antibodies, thus indicating that the IVIg recognize the 20F2 idiotope on patient's autoantibodies. These observations further support the concept of the presence in IVIg of anti-idiotypes against autoantibodies associated with human autoimmune diseases.

We have analysed the epitopic and idiotypic specificity of thyroglobulin antibodies in infants, young adults, aged subjects and pregnant women in order to evaluate the changes that occur in the autoantibody repertoire with age in physiological situations. No increase in IgG anti-Tg auto-reactivity in whole serum and purified IgG from serum was observed with aging. However, IgG from elderly individuals exhibited increased reactivity, as compared to other groups of donors, against particular epitopes commonly recognized by both natural and disease-associated Tg-autoantibodies. The acquisition of a distinct epitopic reactivity in aged individuals suggests that qualitative rather than quantitative criteria could characterize alteration in regulation of the autoreactive B-cell repertoire that occurs with aging. No correlation was observed between the age of the donors and expression of a thyroid disease-associated idiotype (T44 Id) by hTg-autoantibodies. The expression of T44 Id on IgG obtained from serum of a small number of pregnant women may be an effect of the modifications of immune system function in pregnancy, which could lead to increased incidence of autoimmunity during pregnancy or in the post-partum period.