Cells and lymphoid organs

Isolation of immune cells form blood

Centrifuge anticoagulated blood

Isolation of leukocytes iwth density gradient

Cells of the immune system

Innate system comprises

Monocytes (macrophages)

granulocytes

Platelets

Dendritic cells

Natural killer cells

Cells of the immune system

Specific system comprises

T Cells or T lymphocytes

B cells or B lymphocytes

Sites of haematopoiesis

Before birth in the yolk sac, up to 2 months in humans

Liver and splee, 6-9 months

Bone marrow in vertebrate species, primary site of haematopoiesis and lymphopoeisis in adult life

Haemmatopoiesis of white blood cells

Hematopoietic stem cell

• myeloid progenitor cell

  • Mast cell

  • Megakaryocyte -→ platelets

  • Easoinophil

  • Basophil

  • Erythocytes

  • monotye → dendritic cell, macrophige

  • neutrophil

• lymphoid progenitor cell

  • T cell

  • B cell → plasma cell

  • NK cell

Myeloid lineage

Granulocytes

• nuetrophils (also konwn as polymorphonucelar cells (PMN;s)

• eosinophils

• basophils

Monocytes

• macrophages

  • dendritic cells

Granulocytes: neutrophils

Major phaocytic cell

First cells that infiltrate an area of infection (bacterial infections)

Induce acute inflammation

MIlk white blood cell count in mastitis mainly due to neutrophils

Granules contain anitbacterial substances (e.g. lysozyme and proteases
granulocyte colony stimulating facto (G-CSF)

Pus contains many dead neutrophils

Granulocytes: eosinophils

Phagocytic cell

Target mainly helminth parasites, but plays also a role in allergic disease (asthma)

granules contain acid hydrolases (azurophilic granules)
degranulation stimulates also degranulation of other immune cells

located in blood, lungs, stomach, gut, skin

granulocytes: basophils

present in blood

least common granulocyte, around 1% of circulating white blood cells

involved in inflammatory immune responses and in acute and chornic allergic diseases

cells contain basophilic granules

granules contain histamin, heparin and serotonin

mast cells

look like basophils, but form a differen heamopoietic lineage

tissue resident cells (brain, blood brain barrier) intestines

contain granules with large amounts of histamin

involved in pathogen protection, allergy, angiogenesis, nut also involved in tissue repair

high affinity receptor fo immunoglobulin E (IgE)

Monocytes

found in blood

can diffferentiate into macrophages or dendritic cellsMa

macorphages

tissue resident cells

show a range of phenotypes from pro-inflammatory to anti-inflammatory

M1 and M2 paradigm

ANtigen presenting cells

dendritic cells

antigen presenting cells

monoctes respond via chemotaxis to

dead cell material (apoptotic cells)

microbes

complement deposition (C5a)

immune complexes

recruitment factors from T cells

M1 phenotype

bactericidal activity

inflammation

immunostimulation

anti-tumoral activity

LPS TNFA, IFNY

M2 phenotype

tissue repair

matrix remodeling

angiogenesis

immunosuppression

pro-tumoral activity

IL4/IL13, IL10, TGFB

Toll like receptors

innate cells, able to sense for conserved structres of pathogens

Opsonisation

Coating of a micorbe with either complement C3b, fibronectin, specific, or natural anitbodies to facilitate phagocytosis

Mechanisms of opsonization

Opsonization: by complement factor C3b and immunoglobulines

Mac proteins, produced by streptococcus pyogenes, block attachment of C3b and immunoglobulins to receprors on macrophages

Phagocytosis process

1. Atttachemtn of the phagocyte to the pathogen

2. Ingestion of the pathogen

3. Fomration of phagosome

4. FOmration of phagolysozome

5. Destruction of pathogen and formation of residual body

   1. Elimination of waste materials

content phagolysozyme

about 50 different degraditve enzymes + other molecules, e.g.

catalase, O2, H2O2, OH-, NOX, myeloperoxidase, lactoferrin, colalgenase, elastase, lysozyme

Macrophages in tissues can be either derived from

blood monocytes or tissue resident macrophages are developed from the embryonic yolk sac and fetal liver

Lymphocyte-dendrite interaction

Dendritic cells activate lymphocytes in the secondary lymphoid organs

Antigen presenting cells

Dendrites, macrohpages, B-cellsA

Antigen presentation

Phagocytosis of microbe or macromolecule

partial degradation

presentation of parts via MHC class II molecules

To fitting TCR from T cellsL

Lymphoid lineage

B cells, T cells, NK cells

Lymphocytes, B and T cells can not be distinguished by light microscopy

B cells differentiate into plasma cells, which are the factoreis of antibodies

B cells mature in bone marrow or in Bursa of Fabricius in birds

T cells mature in the thymus

How ot distinguish between T cells and B lymphocytes

Using serological methods and monoclonal antibodies

• monoclonal antibodies, recognize cell specific differentiation molecules: cluster of desingation CD

• immunochemistry on cells or tissues

cytokine producton

cytokine mRNA

Lymphoid system

All are connected via blood and lymph vessels

Spleen, thymus, bone marrow, lymph nodes, peyers path, adenodis and appendix

drain tissues

Primary lymphoid organs

Production, maturation and education of lymphocytes

bone marrow, thymus, fetal liver, fetal yolk sac, bursa of fabricius(birds), kdiney (fish) peyers patches (in the intestines in sheep)

Secondary lymphoid organs

spleen

lumph nodes

mesenteric lymph node

intestines

tonsils

Secondary lymphoid organs are the sites where immune responses are initiated. Their main function is to facilitate the interaction between lymphocytes (B and T cells) and antigens — allowing the body to recognize and respond to pathogens effectively.

Head kidney in fish

priamry organ for haematopoiesis

Bone marrow (hallow bones)

haematopoiesis and lymphopoeisis and maturation (B cells)

filtratoino f blood, by macrophages, dendrites

containes mature T and B cells, antigen presenting cells (APC) and plasma cells

Bursa of Fabricius

primary lymphoid organ in birds

Proliferation and maturation of B - cells

contains follicles

degrades after a while

bursectomy results in

an impaired humoral immune ssytem

less circulating B cells

fewer specific antibodies

no formation of memory B cells

vulnerable for infectious diseases

Maternal IgG repertoire acts as

memory of infection history

Induction of specific IgM in offspring

early life protection

Specific serum IgM levels are decreased by bursal duct ligation at 2 weeks post hatch

Athymic mice and dogs

nude mice, lack T cell immunity 

Mexican hairless dog, involution of thymus at veyr young age, no impaired immunity

human thymus with lobular structure

medulla and cortex

Histology of the thumus

Hassal’s bodies

concentrically arranged epithelial cells. probably play a role in producing regulatory T cells (Treg), may be also production of growth factors for T cells

Positive and negative selection

Positive selection precedes neg selection, no correct order in figure

pos selection in corte

neg selection in medulla

AIRE

autoimmune regulator

expression of every self antigen by epithelial cells

Bone marrow: pre T cells (thymocyte) migrates towards thymus

proliferation >90% apoptosis

10% enter periphery

Migration of T cells from cortex to medulla

positive selection: TCR fits MHC

if not: death by apoptosis

negative selection: TCR fits MHC plus self-antigen: death by apoptosis

result: TCR fits MHC plus non-self: migration to periphery

Immunology thumsu

no access of foreign antigens into thymus

otherwise, induction of tolerance

so, there is no immune response int he thumus

or inducing holes in the repertoire by depletion of T cells

Peyers patches in lambs are

primary lympod organs

Function and anaotymy of the spleen

antigen filter for the blood (blood-borne pathogens)

therefore, no afferent lymphatic vessels, in contrast ot lymph nodes

encapsulated and compartmentalized viseral organ

trabaecula, connective tissue: framework for splenic structure

red pulp: resrvoir of erythrocytes and platelets

white pulp: lumphoid tissue

drains and filters blood

consists of white and red pupa regions

degradation old erythoryctes and thrombocytes (red pulpa)

no drainage by lymphatic vessels

Spleen - overview picture

white pulpa

rreservoir for red blood cells and platelets

contains periarteriolar lymphatic sheaths (PALS) - T cellr egion close to arteriolar blood vessels

Red pulp

reservoir for red blood cells and platelets

Lymph nodes

encapsulated

strategically located aruond the body

conected - network

filters atnigens in lymph fluid

lymph fluid contains also antigen presenting cells (dendritic cells)

cortex contains primary and secondary follicles and is surrounded by paracortex

germinal centers: secondary follicles with activated and maturing B cells

Migration of dendritic cells

Homing of lymphocytes

Model for homing of lymphocytes

HOming receptors deterine migration pattern

type of homing receptors depends on developmental stage of the lymphocyte

lymphocyte recirculation

HEV’S high endotelial venules

exhcange between bloodstream and lymphatic system

allows immune surveillance, naive lymphocytes enter the secondary lympod organs via HEV’S