The main cell of the specific immune response is the small lymphocyte.
LIMPHOCYT RECIRCULATION
1) B and T lymphocytes constantly enter the blood stream from the peripheral lymphatic tissue via the lymphatics and the thoracic duct and circulate around the body. '
2) They reenter the lymphoid tissue at another site.
3) Lymphocytes form 20 - 40% of the circulating white blood cell Circulating lymphocytes are mainly T cells with a few B cells.
Immune response & elimination of antigen
1) Antigens can enter the body through the mucosa or skin.
2) Meeting the mucosa associated lymphoid tissue or the cutaneous lymphoid tissue.
3) The antigens are carried to the regional lymph nodes via lymphatics
4) If the antigen enters the blood stream it will be filtered by the spleen.
5) Lymphocyte recirculation ensures that B and T lymphocytes are constantly patrolling the body looking for antigen.
6) Antigen will meet the corresponding lymphocytes specific for the antigen →immune response (activation, proliferation and differentiation of lymphocytes)
7) The immune response takes place in the PERIPHERAL LYMPHOID TISSUE(rich in macrophages and dendritic cells).
* At the mucosal or skin surface immune response takes place in the MALT or cutaneous immune system.
* o The immune response to tissue antigens takes place in the lymph node.
* o The immune response to circulating antigens takes place in the spleen.
8) Antibodies from B cells or effector T cells go to the site of infection and eliminate the antigen.
9) The memory cells remain in the lymphoid tissue.
10) The second time the antigen enters there are a large number of antigen specific lymphocytes (memory cells) in the lymphoid organs so the secondary response is faster and greater than the primary response.
CYTOKINES
1) Cytokines are small soluble proteins that act as multipurpose chemical messengers,secreted by a cell, and act on itself or another cell to change the activity of that cell.
2) They play an important role in both non-specific and specific immunity.
3) cytokines Can be produced by a wide variety of cells such as endothelial cells etc.
4) Some cytokines act on the bone marrow to increase cell proliferation and differentiation.
* eg. colony stimulating factors include GM-CSF, G-CSF, M-CSF.
Feature of cytokines
1) ONE cytokine can ACT on many different cells.
* e.g. TNF acts on the liver to produce acute phase proteins and on the Neutrophils to activate it.
2) DIFFERENT cytokines can have the SAME action.
* e.g. TNF from macrophages and lymphotoxin from T cells have the same actions.
3) Cytokines can act on the same cell that produced it (AUTOCRINE ACTION), on nearby cells (PARACRINE ACTION) or on distant cells (ENDOCRINE ACTION).
