1. Jeanne A Pawitan Histology of the immune (lymphoid, lymphatic) system Jeanne Adiwinata Pawitan Dept. of Histology FMUI

2. Jeanne A Pawitan Immune system Cells of the immune system Bone marrow (myeloid tissue) Diffuse lymphoid system °Diffuse lymphoid tissue °Lymph (lymphoid) nodules Lymphoid organs - capsule

3. Jeanne A Pawitan Immune system – defense mechanism Function: protection >< foreign elements °Foreign macromolecules °Invasive microorganisms Viruses Bacteria Others °Transformed cells

4. Jeanne A Pawitan 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 >< animal disease, except AIDS) °Acquired

5. Jeanne A Pawitan Immune response Specific recognition system (specific immune system) °Recognize self >< non self °Component Cellular (lymphocytes B, T) Soluble (Ig) Nonspecific (innate) effector system (non specific immune system) °Amplifies – function – specific system

6. Jeanne A Pawitan 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, Kupffer’s cells, synovial cells – joint cavities, perivascular microglial cells – CNS)

7. Jeanne A Pawitan 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 – 5 th month prenatal LM: °vascular compartment (A., V., sinusoids) °Intervening spaces hemopoietic compartments – meshwork - islands of hemopoietic cells Adventitial reticular cells, reticular fibers

8. Jeanne A Pawitan 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

9. Jeanne A Pawitan Diffuse lymphoid system Non-encapsulated Location: °Lymphoid organs °Mucosa (lamina propria) – mucosa associated lymphoid tissue (MALT) Digestive system (Gut ALT): Peyer’s patches Respiratory system (Bronchus ALT) Urinary system Occur as °Diffuse lymphoid tissue = localized lymphocyte infiltration °Lymphoid nodules (lymphonodulus)

10. Jeanne A Pawitan 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

11. Jeanne A Pawitan Reticular cells Shape: elongate – stellate Nucleus: ovoid – euchromatic Cytoplasm: °Scanty °Acidophilic °Contains RER – few Golgi complex – moderate-well developed Fine filaments – bundles – at periphery

12. Jeanne A Pawitan 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): Peyer’s patches, etc.

13. Jeanne A Pawitan Lymph nodule = primary nodule Consists of °Germinal center = secondary nodule = ovoid area – contains: larger, pale-staining cells Less densely populated pole – light region/zone Densely populated pole – dark region/zone °‘cap’ = corona, cortex, mantle – small lymphocytes – densely packed – facing less dense pole - directed toward Marginal sinus Red pulp Epithelium (MALT)

14. Jeanne A Pawitan Germinal center – diff. B limphocytes- IgG Dendritic (stellate) cells, dendritic macrophages °Silver method °Cellular framework °Radiating processes – desmosomes °Non phagocytic, bind Ag – Ag presenting – activate T lymphocytes Flattened reticular cells – desmosomes: outer boundary Lymphoblast – actively proliferating Lymphocytes: large, medium, small - esp.dark region Transition to plasma cells Plasma cells (scarce, except in tonsils) Macrophages – ↓toward dark region

15. Jeanne A Pawitan Gut-associated lymphoid tissue Isolated lymphoid follicles Peyer’s 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 Peyer’s patches have homing receptors – specific for HEVs of GALT

16. Jeanne A Pawitan Bronchus-associated lymphoid tissue ≈ Peyer’s 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

17. Jeanne A Pawitan Lymphoid organs Thymus (primary lymphoid organ) Lymph nodes (lymphonodus) Spleen (lien) Tonsils (tonsila)

18. Jeanne A Pawitan 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

19. Jeanne A Pawitan Thymus - lobules Cortex – darker °Epithelial reticular cells – endodermally derived – type I, II, III °T lymphocytes (thymocytes): immunologically incompetent  competent °Macrophages Medulla – confluent – lighter °Epithelial reticular cells – endothelially derived- type IV, V, VI °Lymphocytes – less than in cortex

20. Jeanne A Pawitan Thymus – vascular supply Small arteries – capsule – trabecula  corticomedullary junction – capillary beds  cortex - continuous capillary °Thick basal lamina °Sheath – epithelial reticular cells type I (occluding junction) – blood-thymus barrier  medulla – small venules – veins - out

21. Jeanne A Pawitan Thymus – histophysiology Cortex: °T cells proliferate – surface markers – maturation  capable to recognize Self MHC molecules incapable - detroyed Self epitopes °Epithelial reticular cells type I, II Test the ability of T cells:  have  MHC molecules  Epitopes Produce hormones  maturation of T cells  Thymosin  Thymopoietin  Thymulin  Thymic humoral factor

22. Jeanne A Pawitan Maturation of T cells Role of extrathymic hormones °Suprarenal, gonads – adrenocorticosteroids  T cell number in thymic cortex↓ °Thyroid – thyroxin  stimulate epithelial reticular cells - thymulin↑ °Pituitary – somatotropin  promotes T cell development in thymic cortex

23. Jeanne A Pawitan 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

24. Jeanne A Pawitan Lymph node Small, soft, Ø < 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

25. Jeanne A Pawitan 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

26. Jeanne A Pawitan 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

27. Jeanne A Pawitan Lymph node -paracortex Cells °Mostly T cells °APC comes (from outside) – presents epitope-MHC II complex to T helper  Th – is activated – proliferates  width of paracortex ↑ °Activated Th  medullary sinuses  out to area of antigenic activity Postcapillary venules = high endothelial venules (HEVs) - cuboidal °endothelial cells - signaling molecules °Rolling lymphocytes – selectins >< signaling molecules  firmly bound – diapedesis – out to lymph node parenchyma

28. Jeanne A Pawitan Lymph node - medulla Trabeculae – from hilum Medullary cords °Network – reticular fiber – reticular cells °Cells Lymphocytes – migrating from cortex  medullary sinuses Plasma cells Macrophages

29. Jeanne A Pawitan Lymph node - vascularization Artery (hilum)  trabeculae  medulla  medullary cords  °Capillary beds in medulla °Cortex – cortical capillary beds  postcapillary venules (paracortex)  vein - hilum

30. Jeanne A Pawitan Lymph node – histophysiology Lymph - foreign particulate matter  lymph node – macrophages-phagocytosis = filter Site of antigen recognition °APC – antigen (from outside)  lymph node – lymphocytes  presentation of epitope- MHC complex °Ag – trapped by follicular dendritic cells  recognize by lymphocytes

31. Jeanne A Pawitan Lymph node – histophysiology B lymphocytes – recognize Ag  activated  primary lymphoid nodule  proliferates –diff  B memory, plasma cells - secondary lymphoid nodule  °B memory (some)– stay in cortex °B memory, plasma cells leave cortex  medullary cords Plasma cells (10%)– medulla - Ab  medullary sinuses Plasma cells  medullary sinuses  bone marrow – Ab B memory  out to secondary lymphoid organs  2 nd exposure - prompt and potent secondary response

32. Jeanne A Pawitan 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

33. Jeanne A Pawitan 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

34. Jeanne A Pawitan 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)

35. Jeanne A Pawitan 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

36. Jeanne A Pawitan Closed circulation – open circ. Closed circulation °Endothelial lining: terminal arterial capillaries –continuous - sinuses Open circulation °Terminal arterial capillaries – red pulp - sinuses Combination of both

37. Jeanne A Pawitan Spleen (lien) – white pulp Central arteriole PALS: °T lymphocytes °Frequently: lymphoid nodules (B cells) – germinal center = antigenic challenge  central arteriole - periphery

38. Jeanne A Pawitan Spleen (lien) – marginal zone Cells °Plasma cells °T, B lymphocytes °Macrophages °Interdigitating dendritic cells (antigen presenting cells, APC) Marginal sinuses (vascular channels: inter- endothelial spaces 2-3 μm) – esp. surrounding lymphoid nodules  particulate matter – free access to parenchyma

39. Jeanne A Pawitan Spleen (lien) – marginal zone-events APC – search for Ag in blood Macrophages – attack microorganism in blood Circulating B, T lymphocytes in blood stream – enter the white pulp Lymphocytes – contact with interdigitating dendritic cells – if the epitope-MHC complex is recognized  immune respons in white pulp

40. Jeanne A Pawitan 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 > < coagulation Macrophages particularly numerous near sinusoids

41. Jeanne A Pawitan 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

42. Jeanne A Pawitan 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

43. Jeanne A Pawitan 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

44. Jeanne A Pawitan Palatine tonsils Location °Boundary of oral cavity-oral pharynx °Between palatoglossal –palatopharyngeal folds Deep aspect - fibrous capsule Surface – stratified squamous nonkeratinized epithelium  dips into crypts (10-12) - contain °Desquamated epithelial cells °Dead leucocytes, bacteria, other Ag substances °Food debris Inside – tonsilar parenchyma °Lymphoid nodules – many with germinal centers = B cell formation

45. Jeanne A Pawitan Pharyngeal tonsil Location: roof of nasal pharynx Capsule – incomplete, thinner vs palatine Surface: pseudostratified ciliated columnar epithelium – interspersed with patches of stratified squamous epithelium  pleats = shallow longitudinal infoldings °Ducts of seromucous glands  base pleats Inside = palatine tonsil Inflamed  adenoid

46. Jeanne A Pawitan Lingual tonsil (several) Location: dorsal surface of posterior 1/3 of tongue Superficial – stratified squamous nonkeratinized epithelium – single cript °Ducts of seromucous minor salivary glands  base of crypt Capsule – flimsy Inside = palatine tonsil