The role of pathogenic B-cell clones in antibody mediated autoimmune disorders

Self-Reactivity in the Dimeric Intravenous Immunoglobulin Fraction

Therapeutic intravenous immunoglobulin (IVIg) preparations contain antibodies reflecting the cumulative antigen experience of the donor population. IVIg contains variable amounts of monomeric and dimeric IgG, but there is little information available on their comparative antibody specificities. We have isolated highly purified fractions of monomeric and dimeric IgG by size-exclusion chromatography. Following treatment of all fractions at pH4, analyses by immunodot and immunocytology on human cell lines showed a preferential recognition of autoantigens in the dimeric IgG fraction. Investigation of the HEp-2 cytoplasmic proteome by 2D-PAGE, Western blot, and subsequent identification of IVIg reactive spots by mass spectrometry (LC-MS/MS) showed that IVIg recognized only a restricted set of the total proteins. Similar experiments showed that more antigens were recognized by the dimeric IgG fraction, especially when the dissociated dimer fraction was used, as compared to its monomeric counterpart. These observations are consistent with idiotype-anti-idiotype masking of auto-specific Abs in the dimeric fraction of IVIg.

Using cDNA microarrays to identify human CD19+ B cell gene products (ESTs) originated from systemic lupus erythematosus susceptibility loci

Systemic lupus erythematosus (SLE) is a prototype of autoimmune disease which arises from interactions between susceptibility genes and environmental factors. Despite the heterogeneous manifestations in this disease, all SLE patients present plasma autoantibodies recognizing nuclear components. Thus, auto reactive B cells represent key effectors to be investigated. Human linkage analysis is providing the localization of susceptibility loci distributed in chromosomes contributing to elucidate the manner in which interactions between these loci mediate SLE pathogenesis. We associate the cDNA microarray technology to investigate the differential gene expression of CD19(+) B cells with genetic linkage data. Bioinformatics programs served to evidentiate the differentially expressed sequences and the design of the microarray allowed hierarchical clustering of patients and controls. Sequencing allowed the identification of 8 new gene products differentially expressed (ESTs) that were co-localized in SLE or other autoimmune diseases susceptibility loci on chromosome 1p21, 2q21, 13q33, 16p12.1 and 16q12.1. These findings strongly suggest that chromosomal regions previously identified as SLE susceptibility loci are in fact transcribed in CD19(+) B cells of patients. In this review, we delineate a new possibility for the use of cDNA microarrays in studies focusing the control of gene expression of disease susceptibility loci identified by genetic linkage.