بسم الله الرحمن الرحيم LYMPHOID TISSUE

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

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

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+

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.

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

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

SMALL LYMPHOCYTES (زيادة عن المقرر)

LEUCOCYTES (زيادة عن المقرر)

DEVELOPMENT OF LYMPHOCYTES (زيادة عن المقرر)

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

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

LYMPHOID TISSUE

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.

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

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

Bronchial-associated lymphoid tissue

LYMPHOID NODULE

LYMPH NODES

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

High endothelial venule (postcapillary venule)

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.

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.

Medulla of lymph node

Medullary Lymph Sinusoids (Sinuses)

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.

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

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

SPLEEN

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

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

Splenic microcirculation

Periarterial lymphatic sheath and the central artery

SPLEEN

Lymphoid nodule with central artery

Lymphoid nodule with central artery

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

SPLEEN

Red pulp: 1) Blood sinusoids 2) Pulp cords

Blood sinusoids of spleen

(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.

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.

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.

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.

Splenic microcirculation

Blood sinusoids of spleen

Tonsils Palatine Tonsils. Pharyngeal Tonsil. Lingual Tonsils.

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

PALATINE TONSILS

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.

PHARYNGEAL TONSIL

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.

FUNCTION OF TONSILS Production of antibodies.

THYMUS

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

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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

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

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

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

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

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

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

Involution of Thymus

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