Histology of the immune (lymphoid, lymphatic) system Jeanne

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Histology of the immune (lymphoid, lymphatic)
system

• Jeanne Adiwinata Pawitan
• Dept. of Histology
• FMUI

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Immune system

• Cells of the immune system
• Bone marrow (myeloid tissue)
• Diffuse lymphoid system
• Diffuse lymphoid tissue
• Lymph (lymphoid) nodules
• Lymphoid organs - capsule

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Immune system defense mechanism

• Function protection gtlt foreign elements
• Foreign macromolecules
• Invasive microorganisms
• Viruses
• Bacteria
• Others
• Transformed cells

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Defence mechanism (Martini)

• Non specific defenses
• Physical barriers
• Phagocytes (M, neutro, eosinophils, monocytes)
• Immunological surveillance NK cells
• Interferons, complement system
• Inflammatory responses, fever
• Specific defenses specific immunity specific
  immune response
• Innate (human gtlt animal disease, except AIDS)
• Acquired

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Immune response

• Specific recognition system (specific immune
  system)
• Recognize self gtlt non self
• Component
• Cellular (lymphocytes B, T)
• Soluble (Ig)
• Nonspecific (innate) effector system (non
  specific immune system)
• Amplifies function specific system

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Nonspecific immune system

• Soluble component
• Complement proteins (cytokines)
  lymphokines-monokines interleukines (ILs),
  interferons (IFNs), tumor necrosis factors
  (TNFs), transforming growth factors (TGFs),
  hematopoietic colony-stimulating factors (CSFs)
• Cellular component phagocytes
• Blood neutrophils, eosinophils, monocytes
• Tissue macrophages (alveolar macrophages,
  Kupffers cells, synovial cells joint cavities,
  perivascular microglial cells CNS)

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Bone marrow (red) myeloid tissue

• Location
• central (marrow, medullary) cavity long bones
• Interstices (trabeculae) spongy/cancelous bones
• Soft, gelatinous, highly vascular cellular
  tissue
• Function hemopoiesis 5th month prenatal
• LM
• vascular compartment (A., V., sinusoids)
• Intervening spaces
• hemopoietic compartments meshwork - islands of
  hemopoietic cells
• Adventitial reticular cells, reticular fibers

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Bone marrow cells

• Hemopoietic cells
• Blood cells various stages
• Macrophages destroyed
• Nuclei erythrocytes precursors
• Malformed cells
• Excess cytoplasm
• Adventitial reticular cells
• By age 20 adult cytoplasm - accumulate fat
• adipose cells large reduce hemopoietic
  compartment
• ? yellow marrow

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Diffuse lymphoid system

• Non-encapsulated
• Location
• Lymphoid organs
• Mucosa (lamina propria) mucosa associated
  lymphoid tissue (MALT)
• Digestive system (Gut ALT) Peyers patches
• Respiratory system (Bronchus ALT)
• Urinary system
• Occur as
• Diffuse lymphoid tissue localized lymphocyte
  infiltration
• Lymphoid nodules (lymphonodulus)

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Diffuse lymphoid tissue

• Consists of
• Stroma
• Reticular fibers silver impregnation
• Reticular cells of mesenchymal origin some are
  phagocytic fixed macrophages
• Lymphocytes
• Free macrophages
• Plasma cells

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Reticular cells

• Shape elongate stellate
• Nucleus ovoid euchromatic
• Cytoplasm
• Scanty
• Acidophilic
• Contains
• RER few
• Golgi complex moderate-well developed
• Fine filaments bundles at periphery

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Lymph (lymphoid, lymphatic) nodule, lymphonodulus
lymphoid follicles

• circumscribed-spherical/ovoid-closely
  packed-lymphocytes
• In diffuse lymphoid tissue
• Location
• Lymph node cortex
• Spleen white pulp
• Tonsils
• Lamina propria (MALT) Peyers patches, etc.

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Gut-associated lymphoid tissue

• Isolated lymphoid follicles
• Peyers patches aggregates ileum
• Lymphoid follicles
• B cells
• T cells looser surrounding B Cells
• Numerous APC surrounding B cells
• Simple columnar epithelium ? M (microfold) cells
  capture Ag ? present their epitopes to
  lymphocytes
• Afferent lymph vessels (-),
• Efferent lymph drainage ()
• Received small arterioles ? capillary bed ? high
  endothelial lined venules (HEVs)
• Lymphocytes entering Peyers patches have homing
  receptors specific for HEVs of GALT

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Bronchus-associated lymphoid tissue

• Peyers patches walls bronchus esp.
  bronchi-bronchiole bifurcate
• Epithelial cover pseudostratified ciliated
  columnar epithelium with goblet cells ? M cells
• Afferent lymph vessels (-)
• Efferent lymph drainage ()
• Rich vascular supply ? HEVs
• Possible systemic and localized role in immune
  response
• Lymphocytes entering BALT have homing receptors
  for HEVs of BALT
• Cells mostly B cells, also APC, T cells

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Lymphoid organs

• Thymus (primary lymphoid organ)
• Lymph nodes (lymphonodus)
• Spleen (lien)
• Tonsils (tonsila)

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Thymus

• Location superior mediatinum anterior of great
  vessels (aorta)
• After puberty involution (atrophy) ? adult
  adipose cells
• 2 lobes
• Encapsulated dense-irregular-collagenous
  connective tissue ?septa (trabecula) lobes ?
  incomplete lobules

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Lymph node

• Location interposed in the path of lymph
  vessels-esp.
• Neck, axila, groin
• Along major vessel
• body cavities
• Functions
• Filter remove
• Bacteria
• Foreign substances

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Lymph node

• Small, soft, Ø lt 3 cm
• Capsule fibrous connective tissue (thickened
  at hilum) - trabeculae - adipose tissue
• Convex afferent lymph vessels valves
• Concave hilum A., V., efferent lymph vessels
  valves ? ? medulla

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Lymph node - sinuses

• Sinuses network stellate reticular cells
  macrophages endothelial-like simple squamous
  epithelium migratory lymphoid cells
• Course
• Afferent lymphatic vessels
• Subcapsular sinus
• Cortical (paratrabecular) sinuses
• Medullary sinuses
• Efferent lymphatic vessels

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Lymph node

• Histologically
• Cortex antigen-presenting follicular dendritic
  cells
• Primary lymphoid nodules (virgin B memory B
  cells)
• Secondary nodules (with germinal centers)
  antigenic challenge ?B memory plasma cell
• Paracortex Thymus dependent zone
• Medulla

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Lymph node - medulla

• Trabeculae from hilum
• Medullary cords
• Network reticular fiber reticular cells
• Cells
• Lymphocytes migrating from cortex ? medullary
  sinuses
• Plasma cells
• Macrophages

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Lymph node - vascularization

• Artery (hilum) ? trabeculae ? medulla ?
  medullary cords ?
• Capillary beds in medulla
• Cortex cortical capillary beds ? postcapillary
  venules (paracortex) ? vein - hilum

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Spleen (lien)

• Largest lymphoid organ
• Upper left quadrant abdominal cavity
• Intraperitoneal visceral peritoneum
• Function
• Proliferation B, T cells
• Ab formation blood-borne Ag inactivation
• Elimination of Ag, bacteria, particles, etc.
• Filtering blood destroying old erythrocytes
• Hemopoietic (fetal) adult when needed

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Spleen (lien)

• Convex surface
• Concave surface hilum capsule-thickened
• Arteries nerve fibers (in)
• Veins lymph vessels (out)
• Dense irregular connective tissue capsule -
  occasional smooth muscle cells trabeculae ?
  into the organ

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Spleen (lien)

• Histology
• Network reticular fibers reticular cells
  attached to capsule ? trabeculae blood vessels
• Fresh - cut - parenchyma
• Grey area white pulp
• (Marginal zone 100 µm wide between white
  red pulp)
• Surrounding red area red pulp (splenic cords of
  Billroth)

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Spleen (lien) blood supply

• Splenic artery - hilum ?branching ? trabecular
  arteries (? 0.2mm) ?central arteries
  periarterial lymphatic sheath (PALS) ?
• Radiating - slender blood vessels ? red pulp ?
  (recur) -marginal sinuses marginal zone
• branching ?penicillar arteries red pulp
• Pulp arteriole
• Sheated arteriole Schweigger-Seidel sheath
  macrophages)
• Terminal arterial capillaries splenic sinuses ?
• Veins of the pulp ? splenic vein ?portal vein

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Closed circulation open circ.

• Closed circulation
• Endothelial lining terminal arterial capillaries
  continuous - sinuses
• Open circulation
• Terminal arterial capillaries red pulp -
  sinuses
• Combination of both

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Spleen (lien) white pulp

• Central arteriole
• PALS
• T lymphocytes
• Frequently lymphoid nodules (B cells) germinal
  center antigenic challenge ? central arteriole
  - periphery

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Spleen (lien) red pulp

• ? sponge
• Spaces splenic (venous) sinuses (sinusoids)
• Endothelial lining fusiform ? staves of a
  barrel
• Between endothelial cells - spaces - 2-3 ?m
• Surrounded by reticular fibers (continuous with
  splenic cords) thin strands - longitudinal axis
• Have a discontinuous basal lamina
• Sponge material splenic cords of Billroth
• Reticular fibers (collagen III) loose network
  interstices permeated by extravasated blood
• Stellate reticular cells isolate coll III from
  blood gtlt platelet reaction to coll gtlt coagulation
• Macrophages particularly numerous near sinusoids

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Spleen histophysiology

• Macrophages
• Marginal sinuses macrophage rich
• Periphery of splenic sinuses
• Phagocytosis
• Ag, bacteria, particulate matter, etc
• Old erythrocytes
• Less fkexible (old, malaria) cannot penetrate
  spaces between endothelium
• Surface coat sialic acid residue (-) ? galactose
  moieties exposed induced phagocytosis

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Spleen histophysiology

• Lymphocytes -Ag challenge ? white pulp ?
• B memory cells, plasma cells lymphoid nodules
• T cells (various subcategories) PALS
• ? marginal sinuses ?
• Site of Ag challenge
• Circulating pool of lymphocytes
• Plasma cells
• Some ? stay in marginal zone ? Ab ?marginal
  sinuses
• Most ? bone marrow Ab ? bone marrow sinuses

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Tonsils palatine, pharyngeal, lingual

• Incompletely encapsulated
• Aggregates of lymphoid nodules
• Guard the entrance of oral (oro) pharynx
• Exposed to
• Airborne Ag
• Ingested Ag
• Reaction to Ag
• Forming lymphocytes
• Mounting immune response