بسم الله الرحمن الرحيم

1. بسم الله الرحمن الرحيم

3. Cells of the immune system -monocytes/macrophages -granulocytes/polymorphonuclear cells -(PMN) -mast cells -interdigitating dendritic cells (DC) -follicular dendritic cells -Lymphocytes NK cells B cells CD4+ and CD8+ T cells

8. Lymphocyte

12. Macrophage

13. Macrophage

20. Lymphoid System Basics • Cells, tissues and organs that function to protect body from invasion and damage by foreign cells, microbes, viruses and parasites • Also known as the immune system • Two types of lymphoid tissues: • Encapsulated: connective tissue capsule • spleen, thymus, lymph nodes • Unencapsulated (or partly encapsulated) • tonsils, Peyer’s patches, lymphoid nodules in GI tract, respiratory tract, urinary & reproductive tracts

21. 2 Types of Lymphoid Organs • Central lymphoid organ: where lymphoid precursor cells undergo antigen dependent proliferation and differentiation • T cells in thymus • B cells in bone marrow • Peripheral lymphoid organ: where functional lymphocytes go including lymph nodes, spleen, Peyer’s patches, lymphoid nodules of GI and other tracts

22. Functional categories • Primary lymphoid organs: antigen independent; isolated from outside “world” • Bone marrow • Thymus • Bursa of Fabricius (birds) • Secondary lymphoid organs: antigen dependent; exposed to outside “world” • MALT (BALT, GALT) • Lymph nodes • Spleen

23. Peripheral Lymphoid Tissues • Lymphocytes contact antigens and divide and differentiate into B cells and T cells • Memory cells form that circulate for years to provide extended immunity

28. Thymus 1 • Central lymphoid organ • Thin capsule, lobular organization • Each lobule has cortex (greater cell density) with many T lymphocytes surrounding lighter medulla • Epithelial reticular cells • Hassal’s corpuscles (flattened epithelial reticular cells)

29. Thymus: cortex and medulla

30. Thymus cortex Thymus medulla

31. Thymus 2 • Cortex: many lymphocytes, macrophages, epithelial reticular cells • Medulla: more epithelial reticular cells and fewer lymphocytes • mature T lymphocytes leave from here to go to spleen and lymph nodes • Hassal’s corpuscles: concentric layers of epithelial reticular cells, core degenerated; function/significance unknown • After puberty thymus undergoes involution and increases in connective tissue and adipocytes

35. Lymphatic vessels • Resemble veins (same 3 layers) • Found throughout body except: • Avascular tissues • Central nervous system • Splenic pulp • Bone marrow

37. Lymph Nodes • Number, location and size • 100-200 clustered primarily in neck, thorax, abdomen and pelvis; few in the extremities • Absent from CNS • Usually not located within other organs • Size of watermelon seed to one-third that size • Difficult to palpate

38. Lymph Nodes • Throughout body along lymph vessels • Numerous in axilla, groin, cervical area and thoracic/abdominal mesenteries • Filter lymph before it returns to vasculature • Hilum, concave side, arteries, nerves enter and veins leave • Afferent lymph vessels enter convex surface • Efferent lymph vessels exit hilum

39. Lymph Nodes • Capsule of dense irregular connective tissue with incomplete septa • Reticular fiber network • Cortex: subcapsular sinus, peritrabecular sinuses, several primary and secondary (have germinal centers) lymphoid nodules, venules may have thick endothelium

40. Lymph Nodes • Lymphoid nodule germinal centers have mitotic lymphocytes with surrounding B cells • Outside nodules is paracortical zone where there are many T cells; endothelium may be thickened • Medulla has sinuses which join to form efferent vessels

41. Lymph Node

42. Blood Flow Legend: a:arteriole b: capillary c: post - capillary venule d: muscular venule

44. Lymphatic vessel, lymph node Lymph node

45. Cortex of lymph node with lymphoid nodule Lymph node reticular stain

46. Lymph node medulla Lymph node medulla with sinusoid and medullary cords

47. Spleen 1 • Largest lymphatic organ • Many macrophages; rbc phagocytosis • Capsule of dense irregular connective tissue w/ trabeculae dividing pulp incompletely • White pulp with lymphoid nodules • Red pulp found between sinusoids has reticular fibers, reticular epithelial cells and macrophages

48. White Pulp • Central arteries with encircling lymphoid tissue • T cells form periarterial lymphatic sheaths (PALS) around small arteries • Nodules are mostly B cells • Reticular epithelial cells & macrophages

49. Red Pulp • Reticular cells with cords of cells between sinuses • Cords have macrophages, monocytes, lymphocytes, plasma cells, rbc, granulocytes • Sinuses have irregular lumen, incomplete endothelium and basal lamina

50. Spleen with red pulp and white pulp Spleen red pulp