1. بسم الله الرحمن الرحيم
LYMPHOID TISSUE

2. CELLS OF IMMUNE SYSTEM 1- Lymphocytes: B cells
T cells: memory, TH1, TH2, TC, TS
Natural Killer Cells.
2- Plasma cells
3- Mast cells
4- Neutrophils
5- Eosinophils
6- Antigen presenting cells

3. T-LYMPHOCYTES (زيادة عن المقرر)
Their plasmalemma has:
1- T cell receptors (TCRs).
2- CD molecules or markers
( cluster of differentiation proteins).

4. T-LYMPHOCYTES (زيادة عن المقرر)
SUBTYPES:
1- Memory cells.
2- T helper cells:
Are CD4+
TH1 & TH2 cells
3- T cytotoxic cells (Tc cells) (T killer cells)
4- T suppressor cells ( Ts cells).
N.B. Both Tc & Ts cells are CD8+

5. NULL CELLS (زيادة عن المقرر)
1- Natural killer (NK) cells:
are cytotoxic cells.
antibody-dependent cell-mediated cytotoxicity.
are non-B, non-T cells.
are formed in red B.M.
no need for maturation in thymus.
Kill virally altered cells & tumor cells in non-specific manner.
2- Stem cells.

6. ANTIGEN PRESENTING CELLS (المطلوب فقط ما تحته خط)
1- B lymphocytes.
2- Macrophages.
3- Dendritic cells:
e.g. Follicular dendritic cells,
Interdigitating dendritic cells
Langerhans cells.
4- Epithelial reticular cells of the thymus.
N.B. APCs have class II MHC molecules
(MHC II) but other cells have only MHC I

7. (زيادة عن المقرر) LYMPHOKINES
Are released by:
1- T helper lymphocytes.
2- Antigen presenting cells.

8. SMALL LYMPHOCYTES (زيادة عن المقرر)

9. LEUCOCYTES (زيادة عن المقرر)

10. DEVELOPMENT OF LYMPHOCYTES (زيادة عن المقرر)

11. TYPES OF IMMUNE RESPONSE (زيادة عن المقرر)
Innate Response:(Fast, non-specific, no memory cells)
By: Neutrophils,
Macrophages,
Mast cells,
NK Cells.
(2) Adaptive response:
a- Humoral immune response
b- Cell-mediated immune response

12. TYPES OF IMMUNE RESPONSE (زيادة عن المقرر)
DC: Dendritic cells

13. LYMPHOID TISSUE

14. LYMPHOID TISSUE A) Diffuse lymphoid tissue
B) Encapsulated lymphoid organs:
1- Lymph nodes.
2- Spleen.
3- Tonsils (are incompletely encapsulated)
4- Thymus.
N.B. Both red bone marrow & Thymus are
considered 1ry. Lymphoid organs.

15. DIFFUSE LYMPHOID TISSUE
MALT: lymphocyte infiltration,
solitary lymphoid nodules &
aggregated lymphoid nodules.
- Under the wet epithelial membranes.
Loose C.T is infiltrated with lymphoid cells
(lymphocytes, plasma cells, macrophages,
reticular cells).
- Lymphoid Nodules

16. LYMPHOID NODULE (LYMPHOID FOLLICLE)
1ry. : without germinal center
2ry. : with germinal center

17. Bronchial-associated lymphoid tissue

18. LYMPHOID NODULE

19. LYMPH NODES

20. LYMPH NODE (L.N.) (A) 1- Capsule 2- Trabeculae (septa)
3- Reticular C.T.
Parenchyma: (lymphoid tissue + lymph sinuses)
1- Cortex
2- Paracortex
3- Medulla

25. High endothelial venule (postcapillary venule)

26. CORTEX OF L.N. 1- Lymphatic nodules (follicles):
a- 1ry: without germinal center
b- 2ry: is formed of:
Corona (mantle): Dark, Mostly B-lymphocytes.
Germinal center: Lighter, mostly
activated B-lymphoblasts with macrophages &
dendritic reticular cells.
2- Subcapsular & Cortical (paratrabecular) lymph
sinuses.

27. PARACORTEX Of L.N. It is the thymus-dependent zone of L.N.
It is composed mostly of T-lymphocytes.
It contains high endothelial vessels
(postcapillary venules):
- PCV are lined with cuboidal endothelium.
- PCV are the site of entry of lymphocytes
to L.N.

28. Medulla of lymph node

29. Medullary Lymph Sinusoids (Sinuses)

30. MEDULLA OF L.N. (1) Medullary cords:
are formed mainly of lymphoid cells
( B & T lymphocytes, plasma cells,
macrophages).
(2) Medullary sinusoids ( or medullary sinuses).
N.B. Efferent lymphatic vessels drain lymph with
B & T lymphocytes.

31. MAIN CELLS OF L.N.
1- B & T lymphocytes.
2- Plasma cells.
3- Macrophages
4- Dendritic reticular cells

32. FUNCTIONS OF L.N. 1- Production of immunocompetent cells.
2- Filtration of lymph.

33. SPLEEN

34. STROMA OF SPLEEN
1- Capsule: is covered by visceral layer of peritoneum;
mesothelium.
occasionally contains SMCs
2- Trabeculae.
3- Reticular C.T.

35. PARENCHYMA OF SPLEEN (A) White pulp. (B) RED PULP. (C) Marginal zone.
N.B. No cortex, no medulla.
No afferent lymphatic vessel.

36. Splenic microcirculation

37. Periarterial lymphatic sheath and the central artery

38. SPLEEN

39. Lymphoid nodule with central artery

40. Lymphoid nodule with central artery

41. PARENCHYMA OF SPLEEN White pulp: 1- Periarterial lymphatic sheaths:
housing T lymphocytes.
2- Lymphoid nodules ( with germinal centers):
housing B lymphocytes.
N.B. Both 1&2 have the acentrically located central artery

42. SPLEEN

43. Red pulp:
1) Blood sinusoids
2) Pulp cords

44. Blood sinusoids of spleen

45. (B) Red pulp:
1- Pulp (splenic) cords (of Billroth):
Extravasated blood cells, plasma cells,
Macrophages & reticular cells and fibers.
2- Blood sinusoids:
Are lined with elongated fusiform
endothelial cells with large intercellular
spaces & supported by discontinuous,
hoop-like basement membrane.

46. Between white and red pulps.
(C) Marginal zone:
Between white and red pulps.
Rich in vascular channels (marginal sinuses),
especially surrounding the lymphoid nodules
Rich in avidly phagocytic macrophages.
Contains plasma cells, T & B cells, macrophages, interdigitating dendritic cells.
It houses B cells that are specialized to recognize
thymic-independent antigens.
Site of first entry of B & T lymphocytes from
blood stream to parenchyma of spleen.

47. FUNCTIONS OF SPLEEN 1- Filtration of blood.
2- Phagocytosis of old RBCs &
old blood platelets & invading microorganisms.
3- Production & proliferation of immunocompetent B & T lymphocytes.
4- Production of antibodies.

48. SPLENIC MICROCIRCULATION
1- Splenic artery
2- Trabecular artery
3- Enter the parenchyma as CENTRAL ARTERY ( in the white pulp)
4- Enter the red pulp as several straight branches named PENICILLAR ARTERIES
(pulp arterioles→ Sheathed arterioles→
Terminal arterial capillary)
5- Blood sinusoids
6- Pulp veins
7- Trabecular veins
8- Splenic vein.

49. Splenic microcirculation

50. Blood sinusoids of spleen

51. Tonsils
Palatine Tonsils.
Pharyngeal Tonsil.
Lingual Tonsils.

52. PALATINE TONSILS 1- Epithelium 2- Tonsillar crypts: 10-12
3- Lymphatic nodules
4- Capsule

53. PALATINE TONSILS

55. PHARYNGEAL TONSIL 1- Epithelium 2- Pleats:
Longitudinal infoldings (instead of tonsillar crypts).
3- Lymphatic nodules & diffuse lymphoid tissue.
4- Capsule.
5- Ducts of seromucous glands.

56. PHARYNGEAL TONSIL

57. LINGUAL TONSILS 1- Epithelium.
2- Crypt: a single crypt for each lingual tonsil.
3- Lymphatic nodules.
4- Capsule.
5- Glands: ducts of mucous minor salivary glands open into the base of a single crypt of each lingual tonsil.

58. FUNCTION OF TONSILS
Production of antibodies.

59. THYMUS

60. THYMUS Stroma: 1-Capsule 2-Interlobular trabeculae: incomplete
B) Thymic lobules:
1-Cortex
2-Medulla

61. l

64. CORTEX OF THYMIC LOBULE
A) It contains developing (immature) thymocytes.
98% of thymocytes die?
1-Whose TCRs recognize self-proteins OR
2-Whose CD4 or CD8 molecules can not recognize MHC I or MHC II molecules.
B) Epithelial reticular cells
C) Macrophages

65. CORTEX OF THYMIC LOBULE (cont.)
No lymphatic nodules
No plasma cells
N.B. Tingible body macrophages (resident macrophages with apoptotic bodies)

67. MEDULLA OF THYMIC LOBULE
1-Hassall’s (thymic) corpuscles:
-Concentrically arranged epithelial reticular cells in the medulla.
- Whose number increases with aging.
2-Virgin (naive) mature small T lymphocytes
3- Macrophages
4-Epithelial reticular cells
N.B. Medulla of adjacent thymic lobules are interconnected- Why? Incomplete trabeculae

68. BLOOD-THYMUS BARRIER Site: It is found in the cortex Components:
Continuous blood capillaries
( The only blood vessel in the cortex)
2) Thick basal lamina
3) Sheath of the epithelial reticular cells

69. FUNCTION OF THYMUS Formation, Maturation & Destruction of
T lymphocytes.
Maturation:
Immunoincompetent T cells →→→ Immunocompetent T cells.

70. General notes about thymus
No lymphoid nodules
No reticular fibers
No sinuses or sinusoids

71. Development and Involution of the thymus
It attains its greatest development shortly after birth
It involutes after puberty and becomes infiltrated by adipose tissue
Remnants of thymus remain in adult to form T lymphocytes

72. Involution of Thymus

73. BEST WISHES