THE J CHAIN GENE IS TRANSCRIBED DURING B-LYMPHOPOIESIS AND T-LYMPHOPOIESIS IN HUMANS

In mice and chickens, J chain appears to be expressed only in activate d B cells and plasma cells, In humans, studies based mainly on transfo rmed cells suggest that J chain expression may initiate during earlier stages in B lineage differentiation, In the present study, we isolate d a series of hematopoietic subpopulations from human fetal and adult tissues by immunofluorescence cell sorting and examined each subpopula tion for J chain expression by reverse transcriptase-PCR. In fetal and adult bone marrow, J chain transcripts were detected at all stages of B lineage differentiation, including the progenitor (CD34(+)/CD19(-)) and pro-B (CD34(+)/CD19(+)) cell subpopulations, J chain mRNA was als o detected during fetal thymocyte development: double negative (CD4(-) /CD8(-)) through single positive (CD4(+) or CD8(+)) cell subpopulation s. The J chain message was not detected in peripheral CD3(+) T cells, CD14(+) monocytes, and CD56(+) NK cells from either fetal or adult sam ples, The nucleotide sequence of J chain PCR products from CD34(+)/CD1 9(-) bone marrow progenitors and CD4(+)/CD8(-) thymocytes proved ident ical to the previously reported sequence of functionally spliced J cha in mRNA, These results suggest that the J chain gene is transcriptiona lly active during early stages of both B cell and T cell differentiati on, before the expression of their respective Ag receptors.