Ruth I. Brezinschek

Comparable impact of mutational and selective influences in shaping the expressed repertoire of peripheral IgM+/CD5- and IgM+/CD5+ B cells.

Somatic hypermutation and subsequent selection play a significant role in shaping the peripheral B cell repertoire. This repertoire is composed of CD5+ (5 %) and CD5− B cells (95 %) which are known to traffic through different lymphoid compartments. Previous studies have shown that VH gene usage by CD5+ and CD5− B cells is similar, although mutations are more frequent in the latter. However, the effect of mutation and subsequent selection on the expressed VH repertoire of CD5+ and CD5− B cells has not been delineated in detail. This study, therefore, analyzed the mutational pattern of individual IgM+/CD5+ and IgM+/CD5− B cells. In both populations, mutations can occur without heavy chain isotype switching. Despite the differences in mutational frequency, the patterns of mutation and subsequent selection were comparable in CD5+ and CD5− B cells. These results imply that although mutations are more frequent in CD5− B cells, the overall mechanisms governing somatic hypermutation and subsequent positive and negative selection are similar in CD5+ and CD5− B cells.

Inflammation, immune reactivity, and angiogenesis in a severe combined immunodeficiency model of rheumatoid arthritis

Severe combined immunodeficiency (SCID) mice were engrafted with rheumatoid arthritis (RA) synovium and evaluated to determine whether RA synovial morphology and function were maintained in the RA-SCID grafts. The four major components of RA synovitis, inflammation, immune reactivity, angiogenesis, and synovial hyperplasia persisted in RA-SCID grafts for 12 weeks. Retention of chronic inflammatory infiltrates was demonstrated by histological evaluation and by immunohistology for CD3, CD20, and CD68. Staining for CD68 also revealed that the grafts had undergone reorganization of the tissue, possibly as a result of fibroblast hyperplasia. Immune and inflammatory components were confirmed by the detection of human immunoglobulins and human interleukin-6 in serum samples obtained from grafted animals. Human blood vessels were detected by dense expression of CD31. Small vessels persistently expressed the vitronectin receptor, alpha v beta 3, a marker of angiogenesis. All vessels expressed VAP-1, a marker of activated endothelial cells. Finally, the grafts retained the ability to support immigration by human leukocytes, as demonstrated by the functional capacity to recruit adoptively transferred 5- (and -6)-carboxyfluorescein diacetate succinimidyl ester-labeled T cells. T cells entering the RA-SCID grafts became activated and produced interferon-gamma, as detected by reverse transcriptase-polymerase chain reaction analysis. These studies demonstrate that the RA-SCID model maintains many of the phenotypic and functional features of the inflamed RA synovium.

Similar characteristics of the CDR3 of VH1‐69/DP‐10 rearrangements in normal human peripheral blood and chronic lymphocytic leukaemia B cells

The variable heavy chain (VH) gene segment VH1‐69/DP‐10 has been shown to be over‐represented in B‐cell chronic lymphocytic leukaemia (CLL). Because of certain similar characteristics of their complementarity determining region 3 (CDR3), including preferential utilization of JH6 elements and an extended length, it has been suggested that antigenic stimulation might be involved in leukaemogenesis. Utilizing single‐cell PCR to amplify and sequence genomic DNA from individual normal human peripheral blood B cells, we have obtained 7/421 productively and 1/69 nonproductively rearranged VH genes that used VH1‐69/DP‐10. All productive rearrangements were unmutated, used JH6 and had an average CDR3 length similar to that previously found in VH1‐69/DP‐10‐expressing CLL cells. These results suggest that CLL may arise from B cells commonly found in the peripheral B‐cell repertoire and do not represent expansion of a unique subset of specific antigen‐reactive B cells.