are smaller than phagocytes. They have a large nucleus that fills most of the
cell. There are 2 types of lymphocyte, both of which are produced before birth
in bone marrow.
B lymphocytes (B Cells) remain in the bone marrow
until they are mature and then spread throughout the body concentrating in lymph
nodes and the spleen.
T lymphocytes (T cells) leave the bone marrow and
collect in the thymus where they mature (Thymus-Gland that lies in the chest
just beneath the sternum. It doubles in size between birth and puberty, but
lymphocytes can carry out immune responses. During the maturation process many
different types of B and T lymphocyte develop, perhaps many millions.
is specialised to respond to one Antigen, giving the immune system as a whole
the ability to respond to almost any type of pathogen that enters the body.
mature, all these B and T cells circulate between the blood and the lymph. This
ensures that they are distributed throughout the body so that they come into
contact with any pathogens and with each other. Immune responses depend on B and
T cells interacting with each other to give an effective defence.
Certain T cells co-ordinate the immune response, stimulating B cells to divide and then secrete antibodies into the blood; these antibodies destroy the antigenic pathogens.
cells seek out and kill any of the body’s own cells that are infected with
pathogens. To do this they must make direct contact with infected cells.
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