Chapter10 Immune system Lyu Zhengmei Department of Histology and Embryology, Anhui Medical University
Ⅰ.General Introduction Function ------ Defense The human body immune system has the ability to distinguish self from non-self, to fight against foreign molecules, and destroy microorganisms, abnormal cells or even cancer cells in own body. Abnormally, the immune system of individual reacts with its own normal body tissues or molecules, causing autoimmune disease.
Components of immune system 1. immune cells 2. lymphoid tissue 3. lymphoid organs
1. immune cells lymphocytes Macrophage and MPS antigen presenting cells (APCs) MPS: Mononuclear phagocytic system
Lymphocytes T : Thymus dependent lymphocytes B: Bone marrow dependent lymphocytes NK: Natural killer cells
Mononuclear phagocytic system (MPS) MPS has intense phagocytic activity, involving in immune response. The cells of MPS originate from monocyte and distribute throughout the body. Function: phagocytosis
Name Cells of MPS Distribution Monocyte Macrophage Kupffer cell Dust cell Osteoclast Microglia Blood C.T., lymph node Liver Lung Bone CNS
Antigen presenting cells(apcs) APCs have the capacity to capture the antigens, and digest the protein. The lymphocytes can only recognize the small peptides presented by APCs. In this way, APCs present the antigens to lymphocytes and elicit the immune response. includes macrophages, dendritic cells and B lymphocytes.
Dendritic cells Dendritic cells include Langerhans cells in epidermis Interdigitating cells in spleen and lymph nodes Follicular dendritic cells in lymphoid nodules Langerhans cell in skin Dendritic cells in vitro
2. lymphoid tissue Formed by reticular tissue immune cells
Lymphoid nodule spherical or ovoid; have a clear boundary; mainly composed of B cells; primary and secondary ~ secondary lymphoid nodule Cap Germinal center
diffuse L.T. and lymphoid nodule
2. lymphoid tissue diffused lymphoid tissue lymphoid nodule/ lymphoid follicle
Diffuse lymphoid tissue Irregular in shape, no clear boundary mainly consists of T cells
3. lymphoid organs Central lymphoid organs Thymus: the developing site of T cell Bone marrow: the developing site of B cell Peripheral lymphoid organs Lymph node Spleen Tonsil
Features of central lymphoid organs: develop earlier (fetal period ) place for stem cells to proliferate and differentiate send lymphocytes to peripheral lymphoid organs two weeks before born
Features of Peripheral lymphoid organs: Develop later (after birth) lymphocytes come from central lymphoid organs cell proliferation need antigen stimulating ( antigen dependent) site of immune reactions take place
Ⅱ. Thymus At birth the thymus weighs 10~15g. increases to 30~40g at puberty, then undergoes involution after puberty. much of the organ is gradually replaced by fat tissue in elderly one. However, the thymus is believed to produce T-lymphocytes throughout life.
Thymus of the elderly
Structure of thymus: Capsule ( C.T.) interlobular septa Cortex Epithelial reticular cell (ERC) Lymphocyte: thymocyte Macrophage: secrete IL-1 ERC Medulla thymocyte: a few Macrophage: secrete IL-1 Thymic corpuscles
Capsule Thymus Cortex Medulla
Cortex Medulla The Lobule of Thymus
1. Cortex Epithelial reticular cell star-like with processes, forming a framework. Function secreting thymosin and thymopoietin supporting and nursing
The cortex of thymus
Thymocytes densely packed in various stages of differentiation and maturation. Negative selected and positive selected 95% of thymocytes in cortex are destroyed by epithelial reticular cells and macrophages. Only 5% of thymocytes become T cell. These T cells are essential for normal adaptive immune reactions.
? Where do the thymocytes develop and differentiate in the thymus? The cortex in the thymus. So, how to ensure a stable environment for lymphocytes development in the cortex? Blood-thymus barrier
Blood-thymus barrier Prevents circular antigens from reaching the thymic cortex where T cells are being formed endothelial cell of continuous capillary very thick basement membrane perivascular space with macrophage in it basement membrane of ERC ERC or their processes with desmosome
thymocyte Epithelial reticular cell (ERC) basement membrane of ERC basement membrane perivascular space endothelial cell of continuous capillary macrophage Blood-thymus barrier
2. Medulla Many epithelial reticular cells A few mature thymocytes(t cells) Thymic corpuscles (Hassall corpuscles) Cortex Medulla
Formed by concentric layers of epithelial reticular cells. Acidophilic and regeneration centrally Their function is unknown, but they are characteristic structure of thymus. Thymic corpuscles
Function of thymus the thymic ERC can secrete thymic hormones (thymosin, thymolin, thymopoietin) the site of T lymphocyte development
Ⅲ. Lymph node Situate along the course of the lymphatic vessels structure Capsule---trabecular parenchyma Cortex medulla
Lymph node
1. Cortex lymphoid nodules paracortical zone (thymus dependent zone) cortical sinuses
1) Outer cortex: Lymphoid nodules 2) Paracortical zone diffuse lymphoid tissue B cell mainly, T cells mainly, macrophages, APCs postcapillary venules 3) cortical lymphatic sinuses subcapsular sinuses peritrabecular sinuses
The cortex of lymph node
Paracortical zone----- thymus dependent zone
Lymphocytes can pass this vessel through the endothelia. postcapillary venules High endothelium.
cortical lymphatic sinuses
2. Medulla medullary cords medullary sinuses trabeculae
Medullary cord The lymphoid tissue is arranged in the form of cords which contain B cells, T cells, plasma cells, macrophages and mast cells. Medullary sinuses similar to cortical sinuses, more irregular more macrophages
Medulla of LN
Medullary sinuses
Medulla--- SEM
3. Lymph circulation in lymph node Afferent lymphoid vessels Subcapsular sinuses Peritrabecular sinuses Medullary sinus Efferent lymphoid vessels
4. Functions of lymph node 1 Filter the lymph 99% of antigens and other debris are filtered by lymph node. 2 Give rise to the immune response both T cells and B cells both cellular and humoral immune response
Pathway Recirculation of lymphocytes Lymphoid organs or tissues Postcapillary venules Efferent lymphoid vessel (Lymph circulation) Blood circulation
Diagram illustrating the recirculation of lymphocytes
Recirculation of lymphocytes 1 An efficient surveillance. 2 Promote the communication among immune system. 3 Provide for more rapid and more persistent immune responses.
Ⅳ. Spleen located in the course of blood vessels Capsule----trabecular structure white pulp parenchyma red pulp marginal zone
Spleen Capsule trabeculae White pulp
1. white pulp periarterial lymphatic sheath: T cells thymus dependent zone lymphatic nodules (splenic nodules): B cells marginal zone lies between the white pulp and the red pulp
The white pulp of spleen periarterial lymphatic sheath splenic nodule
2. red pulp splenic sinusoid long rod endothelial cells ; gaps between the adjacent cells; no basement membrane; surrounded by reticular fibers splenic cord the main components are B, M, etc; is the principle place for filtration of blood
long rod endothelial cells
The red pulp of spleen splenic sinusoid
splenic sinusoid
3. Blood supply of spleen splenic A trabecular A central A marginal sinuses penicillar Arterioles splenic sinuses splenic cords pulp venule trabecular vein splenic vein
Blood supply of spleen
Functions of spleen immune responses take place filter blood, destruct aged red blood cells hemopoiesis potence blood storage 50ml
Key points 1. The types of lymphatic tissue 2. The general structure and function of thymus, lymph node and spleen. 3. What areas are thymus dependent zone of lymph node and spleen 4.The components of the blood-thymus barrier. 5. What is thymic corpuscle?
Assignments 1. Describe general structures and functions of thymus, lymph node and spleen. 2. What does blood-thymus barrier consist of?