The bone marrow compartment is modified in the absence of galectin-3.

Galectin-3 (gal-3) is a ß-galactoside binding protein present in multivalent complexes with an extracellular matrix and with cell surface glycoconjugates. In this context, it can deliver a variety of intracellular signals to modulate cell activation, differentiation and survival. In the hematopoietic system, it was demonstrated that gal-3 is expressed in myeloid cells and surrounding stromal cells. Furthermore, exogenous and surface gal-3 drive the proliferation of myeloblasts in a granulocyte-macrophage colony-stimulating factor (GM-CSF)-dependent manner. Here, we investigated whether gal-3 regulates the formation of myeloid bone marrow compartments by studying galectin-3(-/-) mice (gal-3(-/-)) in the C57BL/6 background. The bone marrow histology of gal-3(-/-) mice was significantly modified and the myeloid compartments drastically disturbed, in comparison with wild-type (WT) animals. In the absence of gal-3, we found reduced cell density and diaphyseal disorders containing increased trabecular projections into the marrow cavity. Moreover, myeloid cells presented limited capacity to differentiate into mature myeloid cell populations in gal-3(-/-) mice and the number of hematopoietic multipotent progenitors was increased relative to WT animals. In addition, bone marrow stromal cells of these mice had reduced levels of GM-CSF gene expression. Taken together, our data suggest that gal-3 interferes with hematopoiesis, controlling both precursors and stromal cells and favors terminal differentiation of myeloid progenitors rather than proliferation.

Kinetics of mobilization and differentiation of lymphohematopoietic cells during experimental murine schistosomiasis in galectin-3 -/- mice.

Galectin-3 (gal-3), a beta-galactoside-binding animal lectin, plays a role in cell-cell and cell-extracellular matrix interactions. Extracellular gal-3 modulates cell migration and adhesion in several physiological and pathological processes. Gal-3 is highly expressed in activated macrophages. Schistosoma mansoni eggs display a large amount of gal-3 ligands on their surface and elicit a well-characterized, macrophage-dependent, granulomatous, inflammatory reaction. Here, we have investigated the acute and chronic phases of S. mansoni infection in wild-type and gal-3(-/-) mice. In the absence of gal-3, chronic-phase granulomas were smaller in diameter, displaying thinner collagen fibers with a loose orientation. Schistosoma-infected gal-3(-/-) mice had remarkable changes in the monocyte/macrophage, eosinophil, and B lymphocyte subpopulations as compared with the infected wild-type mice. We observed a reduction of macrophage number, an increase in eosinophil absolute number, and a decrease in B lymphocyte subpopulation (B220(+/high) cells) in the periphery during the evolution of the disease in gal-3(-/-) mice. B lymphopenia was followed by an increase of plasma cell number in bone marrow, spleen, and mesenteric lymph nodes of the infected gal-3(-/-) mice. The plasma IgG and IgE levels also increased in these mice. Gal-3 plays a role in the organization, collagen distribution, and mobilization of inflammatory cells to chronic-phase granulomas, niches for extramedullary myelopoiesis, besides interfering with monocyte-to-macrophage and B cell-to-plasma cell differentiation.