This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Immunology, Subject name: Microbiology
B cells are processed in 
Select and explain. 
A. Bone marrow, B. Liver, C. Spleen, D. Lymph nodes
A: Bone marrow
Answer: A: Bone marrow 
Explanation: Ans. a (Bone marrow). (Ref: Ananthnarayan, Microbiology/6th 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 helper/inducer T-cells, cytotoxic supressor cells.