The rabbit is an excellent model for studying the decline ofB lymphopoiesis with age. The long bones of rabbits fill up with adipocytes startingat 2 months of age, resembling the bone marrow of humans over the age of 60. Workin our lab has shown that factors secreted by adipocytes arrest B celllymphopoiesis beyond the pre B cell stage. The identification of the factorsand their mechanisms is an ongoing process in our lab.

Adipocytes, osteoblasts and chondrocytes arise from a commonprecursor, the mesenchymal stromal cell, also called mesenchymal stem cell(MSC). We are characterizing MSCs isolated from rabbits of various ages toassess which mechanisms within the cells lead to preferred differentiation intoadipocytes to the expense of osteoblasts. We propose that an underlyingepigenetic shift occurs with age or hormonal maturity leading to theaccumulation of adipocytes and decline of B cell lymphopoiesis.