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Unformatted text preview: Immunology 3 The cells of the immune system derive from precursors in the bone marrow Both innate and adaptive immune responses depend upon activation of WBCs (leukocytes) Leukocytes originate in the BONE MARROW many also develop and mature there Immune cells are found in: blood, lymph, central lymphoid organs, periperhal lymphoid organs, MOST tissues (some exceptions) Bone marrow= spongy material found in LONG BONES=contains developing immune cells and erythrocytes, connective tissues and fat Once mature: migrate to guard the peripheral tissues: some of them reside within tissues, while others circulate in the bloodstream and in the lymphatic system (drains extracellular fluid and free cells from tissues, transports them through the body as lymph, and eventually empties back into the blood system All cellular elements of blood (RBCs, platelets-clotting, WBCs)= derive from hematopoietic stem cells of the bone marrow=pluripotent Hematopoiesis= process which generates blood cells; occurs in: adults=bond barrow; fetus=egg sackliverbone marrow (starts in early embryonic development) Also give rise to cells of more limited developmental potential=immediate progenitors of RBCs, platelets and the 2 main categories of WBCs (lymphoid and myeloid lineages) Immune cells=WBCs: 1. Lymphocytes (smaller) 2. Myeloid cells (larger) Pluripotent stem cell= capable of infinite proliferation (reproduction)=capable of differentiating into erythrocytes and all immune cells of the myeloid and lymphoid lineages Platelets and Erythrocytes Platelets: stem cell differentiates into a megakaryocyte= fragments into small cells without nucleusplatelets=aid in the clotting of blood Erythrocytes: stem cell differentiates into a erythroblast= ejects nucleus, forming an erythrocyte=carries O2 and CO2 **start off with pluripotent stem cell NO nucleus no DNA Erythrocytes (RBCs)-no nucleus Most common cell in our blood=long lived (half life of 100-120days)=circulate every 20secs Transport O2 and CO2 No apparent immune function NO NUCLEUS in mammals nucleation is an indication of hematopoietic disorders or anemia**exception=llamas and camels Platelets-clotting Small (2-3 micrometers) Stop bleeding by forming a thrombus=platelets glued together with clotting factors Platelets release: pro-inflammatory (immune stimulating) signals and pro-healing growth factors Dont engage directly in immune response Lymphoid Cells B, T and NK cells B and T cells respond to antigens=cells of adaptive immune system: Upon encountering cognate antigen, these cells proliferate and differentiate into mature (active cells) Active B cells(plasma cells) secrete large quantities of antibodies CD4+ T-cells regulate immune responses CD8+ T cells=cytotoxic lymphocytes=kill host cells displaying the T-cells cognate antigen:MCH complex Relatively large nucleus compared to cytoplasm NK cells detect missing self=part of INNATE immune system:...
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- Spring '11