In what tissue do B and T-lymphocytes originate? What are the two steps involved in lymphocyte “maturation"?
1 Answer
Both B and T-lymphocytes originate in the bone marrow; however, T-lymphocytes maturate in the thymus (a gland in the mediastinum, superior to the heart and sternum, inferior to clavicula).
Explanation:
B-lymphocytes develop and maturate in the bone marrow and they pass through the two-step process in order to enter the blood. The first step is positive selection in which antigens of B-lymphocytes have to bind to a ligand. If not the development is stopped. The second step is negative selection in which B-lymphocytes mustn't bind to self-antigens in order to enter the blood. If they do, there are some mechanisms by which this problem is solved.
T-lymphocytes have several stages of maturation. First, they are negative cells, neither CD8+ or CD4+. Then, in their development, they become double positive CD8+ and CD4+. And, finally, they become either CD8+ or CD4+. In addition to that, there are also positive and negative selections which are pretty much similar to those of B-lymphocytes; however now is either MHC I or MHC II antigen that they areinteracting. Depending whether they interact storngly to either of them - they are being killed - however if they interact neither strongly or weakly - they survive.
