<prompt> B cells are processed inBone marrowLiverSpleenLymph nodes  <response>: Ans. a Bone marrow. Ref: Ananthnarayan, Microbiology6th ed., 116 B lymphocytes precursors, pro-B cells develop in the fetal liver during embryonic life and in bone marrow afterwards continuously throughout life. Rearrangement of Ig genes takes place on their becoming preB cell, which synthesize cytoplasmic IgM. T-cell precursors from yolk sac, fetal liver, BM, migrates to thymus during embryonic and post- natal stages. Earliest identifiable cells of T-lineage and CD7 pro T cells, on entering thymus became preT cells immature. These cells mature in extrathymic tissue and become helperinducer T-cells, cytotoxic supressor cells. 