This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Microbiology
Which of the following change is observed following neonatal thymectomy? 
Select and explain. 
A. Decrease in size of germinal center, B. Increased antibody production by B cells, C. Increased bone marrow production of lymphocytes, D. Decrease in size of paracoical areas of lymph nodes
D: Decrease in size of paracoical areas of lymph nodes
Answer: D: Decrease in size of paracoical areas of lymph nodes 
Explanation: T lymphocytes are selectively seeded into ceain sites in the peripheral lymphatic tissues, such as white pulp of the spleen, around the central aerioles and in the paracoical areas of lymph nodes. These regions have been termed as thymus dependent regions as they are depleted after neonatal thymectomy. Secondary to thymectomy, there is a reduction in the size of paracoical regions of the lymph node and periaeriolar tissue in the spleen. In the lymph node the thymus dependent paracoical areas shows depletion of lymphocytes, while there is a loss of lymphoid cells around the small blood vessels in the spleen. Ref: Nutrition, Immunity and Infections By Prakash S. Shetty, Page 44 ; Histology By Ray C. Henrikson, Volume 518, Page 220