Several transplant patients maintain stable kidney graft function in the absence of immunosuppression. Here we compared the characteristics of their peripheral B cells to that of others who had stable graft function but were under pharmacologic immunosuppression, to patients with chronic rejection and to healthy volunteers. In drug-free long-term graft function (DF) there was a significant increase in both absolute cell number and frequency of total B cells; particularly activated, memory and early memory B cells. These increased B-cell numbers were associated with a significantly enriched transcriptional B-cell profile. Costimulatory/migratory molecules (B7-2/CD80, CD40, and CD62L) were upregulated in B cells; particularly in memory CD19(+)IgD(-)CD38(+/-)CD27(+) B cells in these patients. Their purified B cells, however, responded normally to a polyclonal stimulation and did not have cytokine polarization. This phenotype was associated with the following specific characteristics which include an inhibitory signal (decreased FcgammaRIIA/FcgammaRIIB ratio); a preventive signal of hyperactive B-cell response (an increase in BANK1, which negatively modulates CD40-mediated AKT activation); an increased number of B cells expressing CD1d and CD5; an increased BAFF-R/BAFF ratio that could explain why these patients have more peripheral B cells; and a specific autoantibody profile. Thus, our findings show that patients with DF have a particular blood B-cell phenotype that may contribute to the maintenance of long-term graft function.

This study provides evidence for the existence of different transitional B-cell subsets, each displaying unique phenotypic and regulatory functional profiles. Furthermore, the study indicates that altered distribution of transitional B-cell subsets highlights different regulatory defects in patients with different autoimmune diseases.

No abstract

IntroductionAlthough intravenous immunoglobulin (IVIg) is widely used to treat idiopathic thrombocytopenic purpura, Kawasaki disease, systemic lupus erythrematosus and Guillain-Barré syndrome, 1 the mechanisms by which immune functions are influenced by such preparations remain to be delineated. 2 Because B lymphocytes play a central role in the immunopathologic processes that cause these diseases, several studies have suggested that B cells are the target cells for the beneficial effect of IVIg. For this hypothesis to apply, IVIg would modulate a broad range of B lymphocyte functions including activation, proliferation, 3 and survival. 4 In other words, IVIg would interfere with the expression of genes and, potentially, the functions of proteins involved in cell growth and death.The interaction between IVIg and B lymphocytes could thus modulate intracellular signaling resulting from the engagement of the B-cell antigen (Ag) receptor (BCR). The earliest signaling events of the ensuing cascade involves activation of the Src-family protein-tyrosine kinase (PTK) Lyn. 5 Activated Lyn phosphorylates immunoreceptor tyrosine-based activation motifs (ITAMs) on the cytoplasmic domain of the membrane ␣ and ␤ proteins (CD79␣ and CD79␤). Once phosphorylated, CD79␣ and CD79␤ recruit another PTK protein, Syk. Syk associates with phospho-ITAMs via its tandem Src-homology 2 (SH2) domains, is phosphorylated, and in turn, phosphorylates the adaptor protein B-cell linker protein (BLNK). The adaptor thus acquires the capacity to bind to and activate Bruton's tyrosine kinase (Btk). This sequence of signaling events leads to the activation of phospholipase C␥2 (PLC␥2), hydrolysis of phosphatidylinisitol-4,5-bisphosphate and the production of inositol-1,4,5-trisphosphate.As a result, released intracellular calcium synergizes with other signals to induce gene transcription. 6 This promotion implies the recruitment of several transcription factors (TFs) that influence B-cell proliferation, differentiation, cytokine production, and apoptosis. 7,8 The outcome of BCR engagement is variable, depending on the status of the B cell and commitment of coreceptors. The latter dictate the ultimate response and associate positive regulators (such as CD19 and CD21) and negative regulators (such as CD22 and CD32) and these ultimately determine the outcome of B-cell responses. Under normal conditions, both groups of proteins are expressed at varying levels on the surface of all B lymphocytes and their engagement contributes to setting the threshold of B-cell activation. This is often achieved by increasing or decreasing tyrosine phosphorylation, thereby enhancing or reducing signal transduction. 9 CD22 conveys the SH2 domain-containing phosphatase 1 (SHP-1) over to the BCR through the immunoreceptor tyrosinebased inhibition motifs (ITIMs) located in its cytoplasmic domain. 10 This membrane protein belongs to the sialic acid (SA)-binding Ig-like lectin (Siglec) superfamily, with 7 Ig-like extracellular domains and an amino-terminal Ig domain. CD22 is u...

No abstract

B lymphocytes from chronic lymphocytic leukemia (CLL) display some CD5 transcripts for CD5 containing the known exon 1 (E1A) and other CD5 transcripts containing the new exon 1 (E1B). These malignant B cells, as well as B cell lines transfected with cDNA for E1A-cd5 or with cDNA for E1B-cd5 produce IL-10, raising the possibility that CD5 participates in the secretion of IL-10. We identified transcription factors involved in this production in CD5+ B lymphocytes from CLL patients and in E1A-cd5–transfected or E1B-cd5–transfected Jok cells. STAT3 is activated via phosphorylation of serine 727 but also NFAT2 through its translocation into the nucleus. Chromatin immunoprecipitation experiments confirmed the role of STAT3 and allowed the discovery of a role for NFAT2 in IL-10 production. Both transcription factors bind not only to the enhancer of the Il-10 gene but also to the promoter of the Il-5 and Il-13 genes. Furthermore, transfection of B cell lines with E1A-cd5 or E1B-cd5 established that activation of STAT3 and NFAT2 is regulated by CD5. The same holds true for the production of IL-10, IL-5, and IL-13 and the expression of the receptors for these cytokines. This interpretation was confirmed by two experiments. In the first, downregulation of CD5 by small interfering RNAs lowered the production of IL-10. In the second experiment, transfection of the GFP-NFAT2 gene into B lymphocytes induced nuclear translocation of NFAT2 in CD5+ but not in CD5− B cells. Thus, CD5 expression is associated with NFAT2 activity (and mildly STAT3 activity), indicating that CD5 controls IL-10 secretion.

T lymphocytes and a subpopulation of B lymphocytes express the CD5 coreceptor. Its functional importance is evident from the multiple levels and developmental stages of the regulation of its expression. We here report the discovery of a novel regulatory exon upstream of the noncoding region of the CD5 gene in humans. This alternate exon 1 is designated E1B (with the conventional exon 1 renamed E1A) and was shown to regulate the expression of CD5. E1B-containing transcripts existed exclusively in B lymphocytes and encoded a protein that was truncated and retained intracellularly. As a consequence, the amount of E1A-containing transcripts was down-regulated and the membrane CD5 expression was diminished in the presence of E1B-containing transcripts. High levels of E1A transcripts were found in chronic lymphocytic leukemia, and there were no E1A transcripts in

Previous studies have indicated that mature B cells reactivate secondary V(D)J recombination inside and outside the germinal center (GC) of peripheral lymphoid organs. The nature of the B cells undergoing Ig rearrangement before they enter GC is unknown. In this study, we present evidence that activated mature CD5-positive human tonsil B cells coexpress both RAG1 and RAG2 mRNA and protein, and display DNA cleavage resulting from their recombinase activity. Furthermore, in vitro activation of CD5-negative naive mature B cells by IgR and CD40 cross-linking induces expression of CD5 on a subset of cells, and leads to the up-regulation of RAG1 and RAG2 only in cells turned positive for CD5. Thus, RAG gene expression is closely related to CD5 expression outside GCs. These data suggest that CD5 is associated with receptor revision in activated mature B cells and likely to promote expression of suitable IgR capable of initiating the GC reaction.