The molecular basis of autoimmunity remains largely unknown. One hypothesis is that molecular abnormalities in the means by which the B cell immunoglobulin receptor is assembled or subsequently selected play a role in the tendency to develop autoantibodies. To examine this possibility, a technique has been developed to analyze the B cell receptor expressed by individual B cells without bias. Using this technique, the B cell repertoire expressed by normal individuals has been analyzed in detail. This normal data base has been employed for comparison to determine abnormalities in patients with autoimmune disease. The objective of the current study is to use single cell analysis to delineate the nature of abnormalities in the B cell immunoglobulin repertoire that might underlie autoimmune disease. The characteristics of B cells of patients with systemic lupus erythematosus (SLE) and Sjogrens's syndrome (SS) have been analyzed. The lupus repertoire shows distinct abnormalities, including evidence of enhanced mutational activity, increased receptor editing/revision and clonal expansion, consistent with intense T cell dependent stimulation. By contrast, the B cell repertoire of Sjogren's syndrome patients showed different abnormalities, including restriction of the repertoire, no enhanced mutational activity and limited receptor editing, as well as a pattern of mutations consistent with intense T cell independent stimulation. In neither disease was evidence of molecular abnormalities in receptor assembly obtained. Rather, the data are most consistent with distinct abnormalities in peripheral B cell stimulation, resulting in autoimmunity in these two autoimmune diseases. The capacity to analyze the B cell repertoire without bias has provided new insights into the nature of the abnormalities that predispose to autoimmunity. In systemic and organ-specific autoimmune diseases the B cells of interest circulate between primary and secondary lymphoid tissue and sites of inflammation. In SS, the B cells accumulating in inflamed parotid glands are polyclonal and the repertoire resembles that of the B cells in circulation. However, there is an influx or preferential homing of mutated memory B cells to the inflamed glands, which become sites of B cell proliferation and VH clonal expansion. Representative members of at least one glandular VH clone were among the circulating B cells. Circulating mutated B cells express CD27, which has become a convenient marker for identifying the memory B cell subset. In SLE patients in highly active states of disease, the number and frequency of circulating CD27 high plasma cells was greater than in SLE patients with inactive disease. The proportion of CD27+ B cells related to the duration of disease and therapeutic regiment more than the humoral levels of anti-ds DNA antibodies and circulating immune complexes, suggesting that analysis of this B cell subset may be useful to evaluate and monitor autoimmune disease activity. Ongoing Projects: 1. Homing receptor expression on T & B cell subsets 2. B cell repertoire and mutation analysis of HED-ID, xHIM, CD40def, AID & XP 3. Peripheral & tonsillar B cell subset mutation analysis 4. Absence of memory B cells in ALPS 5. B cell repertoire and mutation analysis in post-transplantation RA 6. Repertoire & mutation analysis of human splenic B cells 7. Repertoire & mutation analysis of anergic B cells in SLE 8. Role of T-regulatory suppressor cells in SLE 9. Synergy of NIK & RAF in NFkB activation 10. B cell repertoire & mutation analysis of SpA superantigen treated macaque 11. B cell repertoire & mutation analysis of ProtL & SpA superantigen treated transgenic huIg murine model 12. B cell repertoire & mutation analysis human stem cell reconstituted SCID/NOD