Autoantibodies to malondialdehyde-modified epitope in connective tissue diseases and vasculitides.

Malondialdehyde (MDA), a peroxidative end-product released during polyunsaturated fatty acid degradation, reacts strongly with lysine residues of cellular proteins. MDA-modified proteins become immunogenic and may elicit specific autoantibody formation. We hypothesized that systemic diseases in which inflammatory events occur, could be an interesting model for studying oxidative stress. A few studies have suggested that MDA-modified proteins may exist in systemic diseases, and that autoantibodies to MDA-modified structures might reflect this oxidative process. Autoantibodies to MDA-modified epitope(s) were therefore assayed in sera of patients with systemic lupus erythematosus (SLE, n = 29), scleroderma (SCL, n = 11), giant cell arteritis (GCA, n = 11), periarteritis nodosa (PAN, n = 10), rheumatoid arthritis (RA, n = 9), and healthy subjects (HS, n = 32). Significantly increased anti-MDA-modified epitope(s) autoantibodies were found in patients with SLE and also in other systemic diseases such as PAN and SCL. Autoantibodies to MDA-modified epitope(s) were predominantly of IgM isotype, with low levels of IgG and no IgA activity. In SLE, anti-MDA-modified epitope(s) autoantibody titres correlated strongly with systemic lupus activity measure (SLAM, r = 0.702, P = 0.0001), anti-nuclear antigen autoantibodies (ANA, r = 0.4, P = 0.029), IgG anti-cardiolipin (r = 0.558, P = 0.03) and the steroid drug regimen (r = 0.52, P = 0.004). Autoantibodies to MDA-modified epitope(s) may reflect oxidative modifications occurring in systemic diseases, and might be useful as clinical markers of SLE activity if further investigated.

Circulating antibodies directed against tryptophan-like epitopes in sera of patients with human African trypanosomiasis.

Human African trypanosomiasis is often associated with an intense proliferation of B lymphocytes, leading to polyclonal antibody synthesis. Using a modified enzyme-linked immunosorbent assay method, we have found highly significant levels of circulating anti-conjugated tryptophan-like epitope antibodies in sera of patients with sleeping sickness. These antibodies were immunoglobulins (Ig) of the M isotype. There was no correlation between immunologic binding and the Ig levels found in sera of patients with human African trypanosomiasis. Higher antibody levels in stage II of the disease than in stage I may be related to damage to the central nervous system. The specificity of this immunologic binding was evaluated by 1) comparison with that obtained with other related conjugates and 2) serum titration. Anti-conjugated tryptophan-like epitope antibodies were not found in other neurologic diseases tested. Their involvement in this pathology remains unknown.

Circulating autoantibodies directed against conjugated fatty acids in sera of HIV-1-infected patients.

Several reports have demonstrated that major changes occur in the fatty acid content of HIV-infected cells. In order to evaluate if these changes are recognized by the immune system, we have attempted to assay the possible presence of autoantibodies (autoAb) directed against conjugated fatty acids (CFA). Using an adapted ELISA, anti-CFA autoAb were assayed in sera of 150 HIV-1-infected patients and 116 controls (healthy donors and patients suffering from other diseases). Significantly increased anti-CFA autoAb of IgG class were found in HIV-1-infected patients (alpha < 0.001). Using our ELISA method and CFA differing in their length and their degree of unsaturation (lauric, myristic, palmitic, palmitoleic, stearic, oleic, linolenic, linoleic, lignoceric, arachidonic, eicosapentaenoic and docosahexaenoic acids), it was demonstrated that the acyl chain of CFA is the immunodominant part recognized by these autoAb. Anti-CFA autoAb were present in 15/52 asymptomatic carriers, 14/36 symptomatic carriers, 16/39 ARC patients, but only 3/23 AIDS patients. Anti-CFA activity seemed to be linked with the CD4+ T cell count, and was not related to the total IgG amounts. Anti-CFA autoAb could result from self-antigen presentation to immunological cells, and may reflect lipid membrane modifications occurring in HIV-infected cells.