B lymphopoiesis takes place in the bone marrow (BM) of many species, including humans, mice, and rabbits. In these species, B lymphopoiesis declines as age increases. I am working to elucidate mechanisms responsible for the loss of B lymphopoiesis with increasing age. In rabbits, B lymphopoiesis is arrested at 2 months of age. B lineage precursors are still present, but there is a block between the common lymphoid progenitor and pre-B cell stages of B cell development. Recent work in our lab suggests there are changes in the BM microenvironment between young and aged rabbits. Of note, there is an increase in adipose tissue in the BM of rabbits 2 months of age and older compared to young rabbits. Adipose tissue is known to secrete factors that affect many processes throughout the body, including the immune system. We now know for humans, mice, and rabbits that adipocytes secrete multiple factors that inhibit B lymphopoiesis in vitro. I study the interplay between adipose tissue and B lymphopoiesis, and am working to identify adipocyte-derived factors that inhibit B lymphopoiesis. After identifying these factors, I plan to determine the mechanism by which these factors inhibit (negatively regulate) B lymphopoiesis. My overall goal is to elucidate the mechanism by which adipocytes inhibit B lymphopoiesis in aged BM, with the intention of identifying targets for therapeutics aimed at reinitiating B lymphopoiesis in aged individuals.