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NBME 20 Answers

nbme20/Block 3/Question#46

Removal of the thymus at birth results in severely ...

Thymic lymphocytes produced before thymectomy are long-lived

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submitted by hayayah(376),

By age 75, the thymus is little more than fatty tissue. Fortunately, the thymus produces all of your T cells by the time you reach puberty. They are long-lived and that's why you can lose your thymus without impairment of your immune system.

sweetmed  Memory T cells live for six months or less in healthy humans (Westera et al., 2013), whereas naive T cells can live for up to nine years +1  
whossayin  so the bone marrow does not take the role of the thymus? +  
dr_jan_itor  @sweetmed, does that mean that if someone loses their thymus, they would develop imunodeficiencies appx 9 years later as the naive T cells have died off? +2  
hpsbwz  @dr_jan_itor no, because once all of the thymocytes become T-lymphocytes, they are stored in lymphoid organs until they're needed. this is why removal of the thymus in MG does not cause any immune system deficiency. +1