Tissues and organs of immune system

Lecture, SFST, 184 /2012

Immune/lymphoid systemstructures and cells innitiate and participate

in the immune response

lymphocytes

mononunuclear – phagocyte system (antigen-presenting cells)

Immune system

innate - non-specific(no immunisation required)o physical barriers (skin,

mucosa, cilia)o biological barriers

(symbionts)o chemical barriers (pH,

mucus)o soluble factors (lysozyme,

interferons, proteins ac.ph., complement)

o cells: phagocytes granulocyteso (rapid answer, restrictive

flexibility, non-specific reaction, no memory)

adaptive – specific(immunisation required)o cells: T - lymfocytes(directly kill cells/ virus-

infected, foreign cells, microorganisms)

o B – lymfocytes (produce)o antibodies(delayed answer, high

flexibility, high specifity, memory and immunity)

Cells of immune system (effect)

non-specific intracelullar killing

macrophages (mononuclear phagocyte system)

produce cytokines APC! neutrophils extracellular killing NK-cells (CD16, CD56), “large, granular lymfocytes“ (perforins, apoptosis), not

MHC restricted eosinophils (granules with

cytotoxic proteins)

specific B-lymphocytes receptor: Igo T-lymphocytes receptor:TCR in complex with

CD, Ag split in peptide fragments in complex with MHC presented by APC

(Tc) MHC I+Ag

(TH) Ag +MHC II presenting by APC

Cells and their functions in immune response

Periods of B and T lymphocytes differentiation in primary/central lymphoid organs

(lymphopoiesis) 1.lymphopoiesis in fetal liver

2.progenitor B and T in bone marrow

3. T-cells precursors transport to the thymus

4.,5. imunocompetent, but virgin/naive B and T-lymphocytes to the periphery (blood, secondary lymphoid organs)

Origin of the cells from pluripotent stem cell - hemocytoblast

dendritic cell

Antigen presenting cells (APC)

heterogenous group of cells monocyte derived dendritic cells (its own progenitor) Langerhan´s cells (skin) M-cells (GIT, intestine) macrophages B-lymphocytes

process Antigen and present epitope with MHC II molecule to T-lymphocytes

Dendritic cells

principal APC originate in bone marrow from its progenitor stem cell

precursors transported by blood to secondary lymphoid organs (T-zone) and non lymphoid organs (Langerhans cells in skin)

endocytosis, processing and antigen presentation to T cells in closest lymphoid tissue (satelite node) – immune response

X folicular dendritic cells – origin in situ, in the stroma of lymph nodes

complex of antigen/antibody in membrane for long time immunological memory

Tissues and organs of immune system

cells: blood, lymph, lymphoid tissue lymphoid tissue: lymphoid nodules, MALT primary or central lymphoid organs: thymus bone marrow secondary or peripheral: capsulated: lymph nodes spleen non-capsulated: diffuse lymphoid system Peyer´s patches appendix tonsils

Lymphoid follicle/ nodule – B-zone

primary and secondary lymphoid nodule

germinal centre – imunoblasts (centroblasts, centrocytes), folicular dendritic cells, macrophages

mantle zone - memory cells marginal zone - non activated B-cells

T- zone

T-lymphocytes dendritic cells (APC for CD4+ a CD8+ T-

lymphocytes) high endothelial venules for homing effect

Lymph node

organs of lymphoid tissue in the course of lymphatics

filter of Ag (microorganisms, tumor cells) coming in the lymph before its return to blood circulation

Lymph node - histology

1. lymphoid tissue structure cortex (lymphatic nodules, B-zone paracortex (T- zone, high endothelial venules) medulla (B-lymphocytes, plasma cells)

2. lymph vessels arrangement (affererent lymphatic vessels – subcapsular sinus – cortical sinuses – medullary sinuses – efferent lymphatics)

3. reticular connective tissue stroma

Lymph node HE (x 30) retikulin (x 30)

Spleen

largest lymphoid tissue accumulation filter of Ag (microorganisms, tumor cells) that penetrate

blood, producing antibodies and activated lymphocytes

Spleen - histology

red pulp white pulp , PALS (T-lymph) + lymhatic nodule (B-lymph) marginal zone (between red and white pulp, active

macrophages)

vascular supply – splenic artery – trabecular arteries – central artery – penicillar artery – sinusoids – trabecular veins – splenic vein

reticular connective tissue stroma

White pulp – lymphoid tissue

lymphoid nodules (B- zone) Malpighian bodies

lymphoid tissue sheath surrounding central arteriole – periarteriolar lymphoid sheath – PALS ( T-zone) T-lymfocyty

marginal zone – 100 um surronds white pulp marginal sinuses and lymphoid tissue macrophages, plasma cells, dendritic cells

Red pulp

specialised vascularised connective tissue arterioles - terminal penicillar arterioles – capillaries –

sinusoids – open circulation splenic cord, of Billroth - lymphocytes, macrophages,

granulocytes, monocytes, erytrocytes, reticular cells

Spleen (x 42)

Thymus - histology

terminal differentiation and proliferation of T- lymphocytes

elimination 95% (apoptosis), negative selection and positive selection

cortex (blood-thymus barries) x medulla (postcapillary venules – mature lymphocytes leave thymus to T-regions in peripheral organs)

reticular epithelial stroma, reticular cells

Dual embryonic origin - endoderm (3rd pair of pharyngeal pouches) + mesenchym (lymphocytes),

Intensive growth till puberty Inborn defect: di George syndrom- thymus aplasia

Thymus HE (x 15)

terminal differentiation and proliferation of T- lymphocytes

elimination 95% (apoptosis), negative selection and positive selection

cortex medulla

Thymus - structure

reticular epithelium epithelial reticular cells, desmosomes paracrine secretion – thymic hormones - maturation of T

cells cortex T - lymphocytes - differentiation, proliferation, selection in

98%, macrophages macrophages blood-thymus barrier – reticular cells medulla reticular epithelial cells, veins

Diffuse lymphoid system

tonsils – aggregates of lymphoid nodules in entrance to the oral pharynx, partly capsulated and covering with epithelium – palatine tonsil, pharyngeal tonsil, lingual tonsil

mucosa associated lymphoid tissue – MALT- lymphoid nodules – aggregates – Peyer´s patches in intestine (ileum)

Lymphocyte distribution

organ T-lymf % B-lymf %

thymus 100 0

bone marrow 10 90

spleeen 45 55

lymph nodes 60 40

blood 80 20