The origins of the self-reactive B cells in the autoimmune diseases systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA) are unknown, but clusters of B, T and dendritic cells, which may act as foci for presentation of self-antigens, are seen in rheumatoid synovial membranes and vasculitic lesions of SLE patients. The objectives of this project are to identify the germline Ig V-genes expressed by the B cells in these clusters, to analyse the pattern of somatic hypermutation in the expressed V-genes and from this, the family history of development of self-reactive B cell clones and whether they are driven by antigen selection.
Clusters of lymphocytes will be excised from stained sections of rheumatoid synovia and vasculitic lesions by micromanipulation. Recombined Ig V-genes will be amplified by PCR, cloned, sequenced and the number of B cell clones which have arisen from independent Ig V-gene recombinations determined. Family trees will be constructed showing the relationships between clone members by the pattern of V-region somatic hypermutation. In a normal immune response, competition for antigen results in selection of B cells with a high replacement to silent (R/S) ratio in hypervariable regions. The R/S ratios of the B cell clones from SLE and RA patients will be analysed to determine whether antigen selection is driving B cell proliferation in the cell clusters. Amino acid substitutions which occur repeatedly, indicative of affinity maturation, will be identified.