Terminal deoxynucleotidyl transferase‐positive B cell precursors in fetal lymph nodes and extrahemopoietic tissues

Abstract

Terminal deoxynucleotidyl transferase (TdT)-positive B cell precursors populate fetal lymph nodes (LN) of mid-term (16th-22th week) fetuses. These cells have a B cell phenotype (HLA-DR, CD45R, CD22, mu) and lack mature differentiation antigens (CD1c, CD20, L26). TdT+ cells are also present in the extranodal mesenteric mesenchyme, pancreas and LN primordia. Extranodal TdT+ cells are found among proliferating (i.e. Ki-67+) B cells and lack leukocyte function-associated antigen (LFA-1) and HLA-DQ; these latter molecules are acquired by nodal TdT+ elements. Adult LN, adult and fetal spleen contain less TdT+ cells than fetal LN. The fetal LN contains the full range of the B cell differentiation compartment, from the TdT+ precursor cell to the mature B lymphocyte.

Transcriptional analysis of the B cell germinal center reaction

“…15 and Fig. 2), suggesting the presence of immature B cells in peripheral lymphoid organs where they are localized outside the GC microenvironment (42)(43)(44). Taken together, our results and these observations indicate that the CD77 marker does not identify the two histologically defined populations of GC B cells.…”

Expression of the recombination-activating genes in extrafollicular lymphocytes but no apparent reinduction in germinal center reactions in human tonsils

“…This conclusion is supported by a previous study reporting the presence of TdT ϩ immature B cells but not T cells in fetal lymph nodes and spleens. 19 However, since the majority of RAG ϩ /TdT ϩ cells did not express lineage-specific markers and since RAG expression in peripheral T-cells has been reported, 20,21 this question requires further examination.…”

“…This conclusion is supported by a previous study reporting the presence of TdT ϩ immature B cells but not T cells in fetal lymph nodes and spleens. 19 However, since the majority of RAG ϩ /TdT ϩ cells did not express lineage-specific markers and since RAG expression in peripheral T-cells has been reported, 20,21 this question requires further examination.The second important observation regards the distribution of RAG ϩ /TdT ϩ cells ( Figure 5). Several recent studies have suggested that expression of the RAGs and other components of the V(D)J recombination machinery may be reinduced in peripheral mature B cells in the context of germinal center reactions, and it has been proposed that this mechanism may rescue B cells producing low avidity antibodies.…”

Stromal cell-derived factor 1 (SDF-1) and antenatal human B cell lymphopoiesis: Expression of SDF-1 by mesothelial cells and biliary ductal plate epithelial cells

“…B cell lymphopoiesis in embryos starts around coelomic cavities: terminal deoxynucleotidyltransferase-positive B cell precursors have been detected in early human fetal mesentery (1), and RAG-1 gene expression in mouse embryos begins in the paraaortic splanchnopleura on day 9 of gestation, 3 days before it starts in the liver (2). Later into gestation, the main site of B cell lymphopoiesis is the liver.…”