Tonsils and spleen begin to develop.
Duration: 4 weeks
West LJ. 2002 Sep-Oct. Defining critical windows in the development of the human immune system. Hum Exp Toxicol 21(9-10):499-505.
Thymus divides into cortex and medulla.
Duration: 2 weeks
West LJ. 2002 Sep-Oct. Defining critical windows in the development of the human immune system. Hum Exp Toxicol 21(9-10):499-505.
Mature T cells (thymus) and B cells (bone marrow) migrate to secondary lymphoid tissue, the lymph nodes, mucous-membrane-associated lymphoid tissue and spleen.
Duration: 2 weeks
Williams CB. 2003. Development of the immune system. In Rudolph’s Pediatrics 21st Edition, Rudolph CD & Rudolph AM, Editors. New York: McGraw-Hill.