Cells & organs of immune system

This presentation gives you the detailed description of various cells & organs of immune systems that participates (particularly, in combination), make communication between themselves to regulate the whole immune system very precisely.

1. 1 Ce lls & organs of immune system Presented by: PRADDUM KUMAR NAMDEV BSc ( hons ) ZOOLOGY Enrollment NO. 17140007 IGNTU Amarkantak MP

2. Cells of immune system 1 Lymphocytes T-lymphocytes B-Lymphocytes NK cells 2. Phagocytic cells Monocytes Macrophages 3. granulocytes Neutrophils Basophils Eosinophils Mast cells 4. Dendriatic cells Organs of immune system A. primary lymphoid organs Bone marrow Thymus B. secondary lymhoid organs: Lymph nodes Spleen MALT 2 contents

3. WBCs are the principle cells of immune system formed hematopoietic stem cell by the process of hematopoiesis. Hematopoiesis occurs in yolk sac during 1st week of gestation. After 3rd month of gestation, hematopoiesis occurs in liver and spleen of fetus and after birth, it occurs in bone marrow. Cells of immune system 3

4. 1. L ymphocytes T-lymphocytes B- lymphocytes NK cell 2. Phagocytic cells Monocytes Macrophages 3. Granulocytic cells Neutrophils Basophils Eosinophils Mast cells 4. Dendritic cells Cells of immune system are: 4

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7. Lymphocytes are small, round cells found in peripheral blood, lymph, lymph nodes, lymphoid organs and in tissues. Lymphocytes represent 20-45% of total cells in peripheral blood and 99% of total cells in lymph and lymph node. According to side lymphocytes are divided into small (5-8µm), medium (8-12µm) and large (12-15µm). Depending on life span lymphocytes are classified into short lived (2 weeks) and long lived (3 years or more or even lifelong). Broadly lymphocytes are divided into three sub-populations, on the basis of function and cell membrane components . T-lymphocytes B-lymphocytes Natural killer cell I. LYMPHOCYTES 7

8. Monocytes and macrophages are mononuclear phagocytic cells. Granulocyte-monocyte progenitor cell differentiates into promonocytes and neutrophil. Promonocytes leaves the bone marrow and enter into blood stream where they differentiate into mature monocytes. Monocytes circulates in blood for about 8 hours, during which they enlarges and then enter into tissues and differentiates into specific macrophages and dendritic cells . II. PHAGOCYTIC CELLS 8

9. Blood monocytes measure 12-15 µm with a single lobed kidney shaped nucleus. It accounts for (2-8%) of blood leucocytes . Immunological Functions of monocytes: Helps in antigen processing and presentation Releases cytokines Specialized function in tissues Cytotoxicity 1. Monocytes 9

10. Monocyte migrates to tissue and differentiates into macrophages. Differentiation of monocytes into macrophages involves following changes: Cell enlarges 5-10 folds Intracellular granules increases in number and complexity Increase phagocytic ability Produces higher level of hydrolytic enzymes and cytokines Macrophages serve different functions in different tissues. Alveolar macrophages : in lungs Histiocyte : connective tissue Kuffer cell: liver Messangial cell: kidney Microglial cell: brain Osteoclast: bone 2. M acrophages: 10

11. Immunological functions of macrophages : Phagocytosis Antigen presentation to T-cell Secretion of lymphokines IL-1, IL-6. IL-12. TNF- α etc. to activates inflammatory response Secretion of granulocyte monocyte colony (GMC) stimulating factors. 11

12. NEUTROPHIL: Neutrophils are (11-14µm) in diameter with multilobed nucleus with granules in cytoplasm . It constitutes 50-70 % of total circulating WBC and remains for 7-8 hours in blood and then migrates to tissues Life span is 3-4 days . Also known as polymorph nuclear (PMN) leucocyte . Neutrophils is stained by both acidic and basic dye. III. GRANULOCYTIC CELLS 12

13. Phagocytic role in acute inflammatory response. It is the first immune cell to responds in inflammation . Immunological functions of neutrophils: 13

14. Eosinophil's are (11-15µm) in diameter, heavily granulated with bilobed nucleus It is stained by acidic dye i.e. Eosin They are phagocytic and motile (migrate from cell into tissue space). Comprise 2-5% of WBCs. Imp. Role in defense against protozoan and helminth parasite by releasing cationic peptides & reactive oxygen intermediates into extracellular fluids. 2. Eosinophils : 14

15. Granules contain various hydrolytic enzymes that kill parasites which are too large to be phagocytosed by neutrophils. Provide allergic inflammation. 15 Immunological functions of eosiniphils :

16. Basophils are non-phagocytic cell found in small number in blood and tissue Cytoplasm contains large number of prominent basophilic granules containing histamine, heparin, serotonin, and other hydrolytic enzymes Stained by basic dyes Immunological functions: Provide anaphylactic and atopic allergic reaction 16 3. Basophils:

17. Precursures are formed in bone marrow and released into the blood in an undifferentiated state, until they rach the tissues. They have ;large numbers of cytoplasmic granules containing histamine. Mast cells and basophils play role in allergic reactions. 17 4. Mast cells

18. Dendritic cells have long cytoplasmic externsions that resembles to dendrites of nerve cell. They have highly pleomorphic with a small central body and many long needle like processes. Dendritic cells are antigen presenting cell (APC) because they possess MHC class . Immunological functions: Involved in antigen presentation to T-cells during primary immune response. Very little role in phagocytosis. 18 IV. DENDRIATIC CELLS

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20. Two main types of organs present in immune system of humans: 1. Primary Lymphoid Organs Bone marrow Bursa of fabricius (in birds) Thymus 2. Secondary Lymphoid Organs. Lymph nodes Spleen Mucosa associated lymphoid tissue (MALT) 20 ORGANS OF IMMUNE SYSTEM

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22. Primary lymphoid organs (PLO) are the major sites of lymphocyte development i.e. lympho­poiesis . Lymphocytes differentiate from lymphoid stem cells, proliferate and mature into functional cells called immuno -competent cells. In mammals, B-cell maturation occurs in the bone marrow and T-cell maturation occurs in the thymus. 22 A. Primary lymphoid organs

23. A . location: It is found in the cavities of most bones in the body including the skull, ribs, sternum, femur and spine . In birds, no bone marrow is found to be present, instead a lymphoid organ named Bursa identified by Fabricius called Bursa of Fabricius , is present and per­forms the same duty of bone marrow of mammals. 23 1. Bone marrow:

24. 2. Structure Bone marrow of different bones mainly consists of a sponge like reticular framework located between long trabe­culae . The spaces in this framework are filled with fat cells, stromal fibroblasts and precursors of blood cells 24 Contd …

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26. 3. Functions: The bone marrow is the main site of generation of all types of circulating blood cells in adult and is the principal site of B-cell maturation and proliferation . During foetal development, the generation of all blood cells, called haematopoiesis , occurs initially in blood island of yolk sac and para -aortic mesenchyme and later in the liver and spleen . Gradually, these func­tions are shifted to bone marrow. All blood cells originate from haematopoietic stem cell and become committed to differentiate along particular lineages ( erythroid , megakaryocyte granulocytic, monocyte and lymphocytic). 26

27. Bone marrow is not only the source of all blood cells but also provides the microenviron­ment for the antigen independent differentiation of B-cell. Besides this, bone marrow serves as a secondary lymphoid organ where mature, virgin, antigen reactive lymphocytes (T & B cell) may respond to antigen, trapped by antigen presenting cells, such as macrophages. Thus , like spleen, bone marrow may provide an antigen processing environment. 27 Contd …

28. I. location Thymus is located in the thora­cic cavity (in the mediastinum), just above the heart and beneath the breast bone. Location of the Thymus in the Chest of Child. II. Origin: In mammals thymus develops from the endoderm of the third and fourth pharyngeal pouch. 28 2. Thymus

29. III . Structure The thymus is flat, bilobed , grey­ish lympho -epithelial organ. Each lobe is made of lobules separated from each other by strands of connective-tissue trabeculae and covered by a capsule. Each lobule con­sists of two compartments the outer com­partment (cortex) is densely packed with immature T-cells ( thymocytes ) And, the inner compartment (medulla) is sparsely populated with mature thymocytes which express CD44 (not found in the cortical thymocytes ). 29 Contd..

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31. There are basically four types of cells found in thymus— Thymocytes dendritic cells epithelial cells M acrophages Both the cortex and medulla of the thymus are criss­crossed by a three dimensional stromal-cell network. 31 Cell types of thymus

32. Out of four cell types, dendritic cells, epithelial cells and macrophages act in a combine manner, as a frame­work to assist in thymocyte matura­tion. Some thymic epithelial cells in the outer cortex, called nurse cells, have long membrane processes which surround as many as 50 thy­mocytes forming large multicellular complexes. Other cortical epithelial cells have long inter-connecting cytoplasmic processes that form a network . The thymocytes are differentiated and matured into different types of T-cells under hormonal influence. Lymphoid progenitor cells formed in the bone marrow migrate to the thymus under the influence of specia­lized thymic environment. 32 Functions of thymus

33. Besides the primary lymphoid organs, there are some other lymphoid organs which are referred to as secondary lymphoid organs. Lymph nodes and spleen are the most impor­tant and highly organized secondary lymphoid organs . Besides these, less organized lymphoid tissue collectively called mucosal-associated lymphoid tissue (MALT) which includes Peyer’s patches in the small intestine, the tonsils, the appendix, as well as numerous lymphoid follicles within the lamina propria of the intestines and in the mucous membranes lining the upper airways, bronchi and genital tract. 33 B. Secondary lymphoid organs:

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35. In case of closed blood vascular system, blood remain always confined within the blood vessels . Lymph and lymphatic system bathe the tissue, tissue fluid and cells. As because lymphatic sys­tem represents an accessory route through which fluids or lymph can flow from interstitial spaces into the blood, which is comprised by tiny lym­phatic vessels . There are different organized lymphoid tis­sues which are located all along the lymphatic vessels, remain as diffuse collections of lympho­cytes and the macrophages and some other are organized into structures called as the lymphoid follicles . 35 Importance of secondary lymphoid organs

36. These two remain as aggregates of vari­ous cells surrounded by a network of draining lymphatic capillaries. These are designated as secondary lymphoid tissues. The secondary lymphoid organs are rich in macrophages and dendritic cells that trap and process antigens in T & B lymphocytes, which mediate the immune responses. The anatomical structure of these organs is designed to facilitate antigen trapping and its maximize opportunities for processed antigen are to be presented to antigen-sensitive cells. 36 Contd …

37. 1. Location: Lymph nodes are located at major junctions of the network of lymph flow through lymphatic channels (lym­phatic vessels. 2. structure: The lymph nodes of man are round or bean shaped structures placed on lymphatic vessels so that they can filter out any foreign material carried in the lymph. Lymph nodes consist of a fibrous reticular network filled with lym­phocytes, macrophages and dendritic cells. Lymphatic sinuses penetrate the node. A sub-capsular sinus is located immediately under the connective tissue capsule of the node; other sinuses pass through the node but are most prominent in a medulla . Afferent lymphatic vessels (those flowing into the node) enter the lymphatics node around its circumference, and efferent lym­phatic vessels (those flowing out of the node) leave from depression (or hilus ) on one side. The blood vessels supplying a lymph node also enter and leave via hilus . 37 I. Lymph node

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41. The interior of a lymph node is divided into three concentric zones—an outer cortex, a para­ -cortex and a central medulla. Each of which pro­vides a distinct micro-environment. The cells in the cortex are predominantly (B-cells) lympho­cytes (arranged in nodules), macrophages and follicular dendritic cells arranged in primary folli­cles. In lymph nodes, these follicles are stimulated by antigen, turned into secondary follicles to expand upto germinal centers where B-cells undergo somatic mutation. 41 Contd …

42. Intense B-cell activation and differentiation into plasma and memory B-cells. It occur in the germinal centers of lymph nodes. Cells that increase their ability to respond to an antigen leave the germinal center to colonize other secon­dary lymphoid organs. Cells with reduced ability undergo apoptosis (programmed cell death) and are removed by macrophages. The para -cortex sometime is referred to as thymus dependant area, in contrast to the cortex, which is thymus inde­pendent area. The para -cortex is largely constitu­ted with T-lymphocytes and dendritic cells. The inter- digitating dendritic cells act as antigen presenting cells (APCS) and thus express class II MHC (Major Histocompatibility Complex) molecules. 42 Contd..

43. The inner most layer of the lymph node is composed of lymphocytes, forming inter connecting strands in the medulla, called the medullary cord. Again these medullary cords surround the medullary sinuses which have plasma cells and some macrophages 43 Contd..

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45. 1. Location Spleen, the secondary lymphoid organ is located high in the left abdominal cavity . The spleen is specially adapted for filtering blood and trapping blood-borne antigens and respond to systemic infec­tions . 2. Structure Spleen is one of the most important lymphoid organ remain sur­rounded by a capsule. From the capsule, a no. of projections called trabeculae remain extended to the interior to form a com­partmentalized structure. 45 2. spleen

46. There are two types of compartments, named red pulp and white pulp . These two pulps are separated by a diffused marginal zone : I. Red pulp: The red pulp of spleen consists of a network of sinusoids. Sinusoids are with huge macrophages and erythrocytes . Function: This splenic zone helps to destroy and remove old and defective red blood cells. Some of the macrophages within the red pulp contain engulfed red blood cells or iron pigments from degra­ded hemoglobin. 46 Contd …

47. II. White pulp This zone is with T-lymphocytes. It surrounds the per arteriolar lym­phoid sheath (PALS). Function : The T-cell-rich-PALS mediate the initial activation of B and T cells. Here , dendritic cells capture antigen and present it with T Helper (TH) cells. In terms these activated T-cells activate B cells. Activated B and TH cells together migrate to primary follicles present in the marginal zone . Primary follicles gradually develop charac­teristic secondary follicles after antigenic challenge and rapidly give rise to B-cells and plasma cells. 47

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49. Besides lymph nodes, spleen, mucosal asso­ciated lymphoid tissue (MALT) is also considered as secondary lymphoid organ. I. Location : The majority of secondary lymphoid tissue in human body is located within the lining of digestive, respiratory and genitourinary tracts. These are collectively called Mucosal Associated Lymphoid Tissue (MALT) There are several types of MALT. Two major MALT includes Bronchial Associated Lymphoid Tissue (BALT) and Gut Associated Lymphoid Tissue (GALT) GALT includes the tonsils, adenoids, and specialised regions in the small intestine called Peyer’s patches. II. Structure: Loose cluster of lymphoid cells are present with little organizations in the lamina propria of intestinal villi to organ­ised structures such as the tonsils, appendix and Peyer’s patches. 49 3. MALT

50. MALTs are meant for the pro­duction of huge antibody-producing plas­ma cells which are very essential for the body defense. 50 Functions:

51. LIFE SCIENCES FUNDAMENTALS AND PRACTICES –I BY: PRANAV KUMAR AND USHA MINA PUBLICATION: PATHFINDER, NEW DELHI WWW.BIOLOGYDISCUSSION.COM WWW.ONLINEBIOLOGYNOTES.COM IMAGE SOURCES SLIDE SHARE GOOGLE IMAGES 51 References

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