Analyses of B cells in the bone marrow and secondary lymphoid tissues have revealed a broad range of cell surface markers defining B cell subpopulations, but only a few of these have been used to analyze B cell subpopulations in peripheral blood (PB). We report here the delineation of circulating PB B cell subpopulations by staining for CD19, CD38, and IgD in combination with CD10, CD44, CD77, CD95, CD23, IgM, and the B cell memory marker CD27. The utility of this approach is shown by the demonstration of disturbances of circulating B cell subpopulations in patients with autoimmune disease. Five mature B cell (Bm) subpopulations were identified in normal PB that were comparable with the tonsillar Bm1, Bm2, early Bm5, Bm5 subpopulations and, surprisingly, to the germinal center (GC) founder cell subpopulation (Bm2′ and Bm3δ–4δ), suggesting that some GC founder cells are circulating. No PB B cells resembled the Bm3 and Bm4 GC cells. Remarkably, some cells with the CD38−IgD+ phenotype, previously known as naive Bm1 cells, expressed CD27. The CD38−IgD+ subpopulation therefore includes both naive Bm1 cells and IgD+ memory B cells. This new classification of B cell developmental stages reveals disturbances in the proportions of B cell subpopulations in primary Sjögren’s syndrome (pSS) patients compared with healthy donors and rheumatoid arthritis patients. Patients with pSS contained a significantly higher percentage of B cells in two activated stages, which might reflect a disturbance in B cell trafficking and/or alteration in B cell differentiation. These findings could be of diagnostic significance for pSS.

Intracellular rheumatoid factor activity is found mostly in IgM plasma cells of rheumatoid synovial membranes from seropositive patients, while tissues from seronegative patients nearly always lack free rheumatoid factor. However, rheumatoid factor activity can be revealed in a considerable number of IgG plasma cells by pepsin digestion of tissues both from seropositive and seronegative patients. This activity has been further characterized by sequential double immunofluorescence staining. It was demonstrated in plasma cells representing each of the four IgG subclasses. The proportion of rheumatoid plasma cells with this activity varied in tissues from different individuals, but in some seronegative cases about 50% or more of the IgG plasma cells contained such‘hidden’ rheumatoid factor. Most of the IgG rheumatoid factors in plasma cells possessed the ability to react with several IgG subclass proteins, and were thus often directed against antigens common to two or more subclasses. The results gave evidence of intracellular blocking of rheumatoid factor activity, due to IgG‐IgG rheumatoid factor complexes. Additional evidence of such plasma cell complexes was obtained by observing an in vitro fixation of the complement components Clq and C3 to such cells. The fixation of aggregated IgG to extracellular deposits and to inclusions in synovial lining cells and joint fluid leukocytes was due to Clq as well as to rheumatoid factor.

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We document here the identification of germinal centres with dark and light zones, a follicular dendritic cell network and clonal expansion in the synovium of rheumatoid arthritis patients. Synovial tissue from 24 patients suffering from rheumatoid arthritis or the polyarticular form of juvenile rheumatoid arthritis were screened for the presence of lymphoid follicles. The synovial tissues of 14 patients contained follicles and four of these had germinal centres and a follicular dendritic cell network. There was a statistically significant association between follicles in the synovium and the presence of rheumatoid factor autoantibodies in the patients' serum indicating a link between local germinal centre formation and the presence of pathological rheumatoid factors. Nucleotide sequencing of monoclonal rheumatoid factors from one of the patients' synovial tissue which contained germinal centres clearly supports the possibility that these rheumatoid factors have gone through a germinal centre reaction. While rheumatoid factors from healthy immunized donors are regulated through a tolerization mechanism which selects against replacement mutations and does not allow affinity maturation, synovial rheumatoid factors seem to lack this tolerization mechanism. The formation of germinal centres where B cells affinity mature and expand at the central site of disease in rheumatoid arthritis may explain why rheumatoid factors in rheumatoid arthritis develop into auto-aggressive antibodies.

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