- ● Acquired immunity is the function of lymphocytes. If a person is born with a lack of lymphocytes for whatever reason, then death usually occurs within days due to massive bacterial infections confirming that lymphocytes are essential
- for survival.
are found primarily in bone marrow, lymph nodes and lymphoid tissues
throughout the body. Lymph nodes
filter the lymph
, while the spleen, thymus, bone marrow and liver
filter the blood
(like the innate response).
● The two principal types of lymphocytes (B's and T's
) are derived as for all blood cells from pluripotent hematopoietic stem cells
(as are all blood cells). Nearly all lymphocytes reside in lymphoid tissues throughout the body, but prior to this they must go through an essential maturation or programming
● Potential T-lymphocytes
first migrate to the thymus
(hence the “T?”) for processing while B-lymphocytes
are processed in the liver
prior to birth and then bone marrow
(hence the “B?”) after and throughout life.
● After migrating to the thymus, T-lymphocytes divide rapidly and diversify extensively
in preparation to respond to a huge array of potential antigenic
substances. Each T-lymphocyte
develops specific reactivity to one antigen
- ● T-lymphocytes then migrate throughout the body to the various lymphoid tissues where they attack
- antigenic material directly (cell-mediated immunity).
- ● While in the thymus, T-lymphocytes are “checked” to ensure that they do not respond to any of the body’s own tissues or “self-antigens” which
- can prove disastrous (by causing an autoimmune
- response). The lymphocytes are exposed to virtually all self-antigens and any that react are destroyed and/or phagocytized (can be >90% of lymphocytes formed!).
● This vital processing occurs principally just prior to and after birth
. After this, the thymus can actually be removed if necessary because after that, it doesn't do much.
- ● B-lymphocytes function differently from T-lymphocytes in two ways (much less is known about B-lymphocyte processing in the liver and bone marrow than for T-lymphocytes):
- 1) B-lymphocytes secrete antibodies that interact specifically with antigens (humoral immunity)
- 2) B-lymphocytes exhibit even greater diversity than the processed T-lymphocytes.
● After processing, B-lymphocytes
migrate throughout the body similarly to T-lymphocytes to similar but not identical locations in lymphoid tissues