Modulation of matrix metalloproteinase-9 (MMP-9) secretion in B lymphopoiesis.

The matrix metalloproteinases (MMPs) are proteolytic enzymes that degrade the extracellular matrix, thus involved in cellular migration. The extent and role of MMPs secretion in primary non-transformed B cells, and specifically during early stages of development in the bone marrow (BM), has been barely unveiled. Herein, we investigated the secretion of MMP-9 during B lymphopoiesis and its modulation in response to different mitogens and cytokines. To do so, we used our BM culture system and well-studied mutated mouse models to isolate the different B cell populations. Our results show that MMP-9 is spontaneously secreted throughout B lymphopoiesis, and that the level of secreted MMP-9 is developmentally regulated. Using reverse transcription-PCR, we found that IFNbetaR is expressed throughout B cell development, while tumor necrosis factor (TNF)-alphaR-p55 and IFNgammaR expressions are initiated only at the pre-B stage. We found that TNFalpha stimulates MMP-9 secretion in transitional cells, whereas IFNs suppress MMP-9 secretion in immature cells. LPS and phorbol 12-myristate 13-acetate suppressed MMP-9 secretion in transitional cells, whereas LPS and concanavalin A stimulated MMP-9 secretion in mature B cells. We conclude that B lymphocyte development is accompanied with MMP-9 secretion and the developing cells are competent to modify this secretion upon different immune stimuli.