An appropriate balance between numbers of lymphocytes and myeloid cells is essential for a healthy immune system. In a recent article published in Nature Immunology (August 2017), Dr. Mari Shinohara and colleagues showed that the protein osteopontin plays important roles in regulating this balance. Expression of an intracellular form of osteopontin in myeloid precursor cells in the bone marrow is regulated by cell density and functions as a switch to control myeloid cell development, with high osteopontin inhibiting and low osteopontin promoting the production of myeloid cells. Interestingly, an extracellular, secreted form of osteopontin has a different effect, as it promotes lymphocyte survival. Regulation of myeloid and lymphoid populations by osteopontin is shown to impact immune responses during infection and autoimmune disease.
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