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Terminal deoxynucleotidyl transferase-positive B cell precursors in fetal lymph nodes and extrahemopoietic tissues
G Cattoretti1, C Parravicini, A Bonati
1Division of Anatomic Pathology, Istituto Nazionale per lo Studio e la Cura dei Tumori, Milan, Italy.
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.
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.