B lymphocytes express and lose syndecan at specific stages of differentiation.

TLDR

Lymphopoietic cells depend on bone marrow stroma interactions and alter matrix adhesion during differentiation, with syndecan acting as a heparan sulfate proteoglycan that mediates binding to collagens, fibronectin, and thrombospondin. We asked whether syndecan is present on the surface of lymphopoietic cells. Syndecan is expressed exclusively on precursor B cells and is lost before B lymphocytes enter circulation, absent on peripheral B cells, and reappears upon differentiation into plasma cells, indicating that syndecan mediates stage‑specific adhesion to extracellular matrix during B‑cell maturation.

Abstract

Lymphopoietic cells require interactions with bone marrow stroma for normal maturation and show changes in adhesion to matrix during their differentiation. Syndecan, a heparan sulfate-rich integral membrane proteoglycan, functions as a matrix receptor by binding cells to interstitial collagens, fibronectin, and thrombospondin. Therefore, we asked whether syndecan was present on the surface of lymphopoietic cells. In bone marrow, we find syndecan only on precursor B cells. Expression changes with pre-B cell maturation in the marrow and with B-lymphocyte differentiation to plasma cells in interstitial matrices. Syndecan on B cell precursors is more heterogeneous and slightly larger than on plasma cells. Syndecan 1) is lost immediately before maturation and release of B lymphocytes into the circulation, 2) is absent on circulating and peripheral B lymphocytes, and 3) is reexpressed upon their differentiation into immobilized plasma cells. Thus, syndecan is expressed only when and where B lymphocytes associate with extracellular matrix. These results indicate that B cells differentiating in vivo alter their matrix receptor expression and suggest a role for syndecan in B cell stage-specific adhesion.