Immunogenicity of rituximab in patients with severe pemphigus.

Pemphigus is a life-threatening autoimmune bullous disease associated with autoantibodies to desmoglein 1 and/or 3. The anti-CD20 chimeric mouse monoclonal antibody rituximab has previously been successfully applied in more than 130 reported pemphigus patients with severe and/or refractory disease. Since antibodies against other therapeutics such as IFNalpha and beta, erythropoietin, and TNFalpha antagonists had led to decreased efficacy of these drugs, we determined anti-rituximab antibodies in 11 patients with pemphigus before rituximab administration as well as 3, 9, and 15 months thereafter. For this purpose, a novel, affinity capture elution assay was established using rabbit IgG against the F(ab)2 fragment of rituximab. In addition, serum levels of rituximab were determined by a competition ELISA. In 2 of 11 pemphigus patients, antibodies to rituximab were detected. In both patients, only a partial remission was observed under treatment. In addition, when followed over a longer period of time, the occurrence of anti-rituximab antibodies paralleled an increase in disease activity. Of the 9 patients without development of antiantibodies to rituximab, in 5, all lesions healed and in 4, partial remissions were seen. These observations show that antibodies to rituximab are generated in some patients during rituximab treatment and may be associated with a less favourable response to treatment.

Comparison of different test systems for simultaneous autoantibody detection in connective tissue diseases.

The serological diagnosis of connective tissue diseases (CTDs) is based on the analysis of circulating autoantibodies to cytoplasmic and nuclear proteins (extractable nuclear antigens [ENAs]). The determination of autoantibody specificities supports the clinical diagnosis of the type of CTD and also often the prognosis of the disease. The former indirect immunofluorescence (IIF) technique still provides a useful screening method that currently is supplemented by a range of different techniques allowing the exact determination of single autoantibody specificities. These ENA profiling techniques include ELISA, immunoblotting, line-blot assays, and flow cytometric bead-based multiplex assays. The novel line immunoassay (LIA) from Mikrogen has been introduced in a recent study as a suitable technique for the simultaneous detection of autoantibodies in a routine clinical laboratory, providing comparable results as ELISA and ELiA (both from Pharmacia Diagnostics) (see Damoiseaux et al., this volume). In this study, LIAs from three different manufacturers were performed in 30 serum samples from patients with dermatological manifestations and 27 samples from SLE patients with renal involvement. The line assays from Mikrogen (recomLine ANA/ENA), Innogenetics (Inno-Lia ANA Update), and Imtec (ANA-LIA) were compared for antigen composition, handling, and statistical analysis including sensitivity and concordance. Autoantibody frequencies detected by the Mikrogen, Innogenetics, and Imtec line assays were 14.0%, 19.3%, and 15.8% for RNP; 14.0%, 22.8%, and 14.0% for Sm; 26.3%, 31.6%, and 40.3% for SSA; 3.5%, 12.3%, and 14.0% for SSB; and 3.5%, 14.0%, and 10.5% for histones. Our studies show that the line assay format is an easy-to-use, sensitive, and specific method for ENA antibody detection in human sera.