BMOL30090 L4 cellular components of innate IS

neutrophil function

bacteria killing, phagocytosis and cytokine production

eosinophil function

bacteria and parasite killers

macrophage function

cytokine production, antigen presentation and phagocytosis

mast cell function

vasoactive peptide production, microbe killing

natural killer cell function

bactericidal and cancer cell killing

dendritic cell function

antigen presentation

monocyte function

bactericidal and parasite killers

immune cell migration

how IICs arrive to site of infection

• makes immune cells differ from other body cells

• can migrate from blood into tissues, be homed to these tissues, and recirculate into blood/lymph

• immune responses: combo of systemic and local events

immune cell infiltration

process occurs due to a succession of tightly coordinated phases. Many molecule types contrib to this process

vasodilation: histamines

• histamine is a biogenic amine synthesised from L-histidine by L-histidine decarboxylase

• mainly found in mast cells

• induces vasodilation

vasodilation: prostaglandins (PGs)

• PGs are made locally after injury, from arachidonic acid (cell memb. lipids) by COX

• PGE2 can be produced from a myriad of cells, immune and non-immune (incl. endothelial cells)

• have similar effects to histamine

• ibuprofen inhibits COX and inhibits prod of PGs (pain)

chemotaxis

movement of cell in response to chemical signal/gradient

how IICs move to where they are needed

what does chemokine stand for?

chemokine - chemotactic cytokine

chemokines and rolling

• released during inflam, injury and infection

• engage chemokine receptors on surface of immune cells

• in IICs, chemokine binding to their receptors promotes:

  • movement towards area of high gradient

  • increased binding affinity of integrins for their adhesion molecule

sources of chemokines

• can be prod by immune cells themselves, epithelium and stroma

• prod in response to PRR engagement or to cytokine stimulation

• some receptors can bind to more than one chemokine - only from corresponding type (some CCs bind to different CCRs, some CXCs to different CXCRs) - COMPLEXITY

chemokine roles

• CXCL1-CXCR2, CXCL8-CXCR1, CXCR2 - attract neutrophils

• CCL2-CCR2 - attract monocytes

• CCR7-CCL21/CCL19 - key for DC migration to LNs

selectins

carbohydrate-binding transmembrane proteins in the surface of immune and endothelial cells

mediate relatively low binding in the initial phase of migration

expression/conformation is increased in response to cytokines and vasoactive peptides

capture and rolling: selectins image

integrins and adhesion molecules

• integrins are proteins expressed in surface of immune cells, which interact with adhesion molecules on the surface of endothelial and stromal cells

• integrins are dimers formed by alpha and beta chains

• transmembrane with intracellular end anchored to the cytoskeleton of the cell

• interaction betw. integrins and adhesion molecules = anchor circulating immune cells to blood vessel wall, allowing rolling and crawling

integrins and adhesion molecules: ligands

ICAM-1 - neutrophils ligand

neutrophils need to be stuck to blood vessel in order to go to site of inflammation

reg. of integrins/adhesion molecules by inflam, factors: image

Step 1.

reg. of integrins/adhesion molecules by inflam, factors

vasoactive substances - blood vessel dilation —> blood flow slows

Step 2.

reg. of integrins/adhesion molecules by inflam, factors

large leukocytes move away from the centre of blood vessels, closer to vessel walls

Step 3.

reg. of integrins/adhesion molecules by inflam, factors

selectin expression —> initial binding

selectins just recognise carbohydrates in cell surface initially

Step 4.

reg. of integrins/adhesion molecules by inflam, factors

cytokine/chemokine promote expression and conformational changes in adhesion molecules/integrins

Step 5.

reg. of integrins/adhesion molecules by inflam, factors

leukocytes crawl on endothelial cells where they find abundant expression of adhesion molecules to tether

Step 6.

reg. of integrins/adhesion molecules by inflam, factors

these abundanrt connections initiate processes inside the endothelial cells that reduce paracellular connections

• rearrangement of endothelial cell cytoskeleton, possible favours their contraction

• phosphorylation of VE-cadherin and destabilisation of cadherin-dependent junctions (triggered by abundant ICAM-1/VCAM-1-integrin connections

Step 7.

reg. of integrins/adhesion molecules by inflam, factors

paracellular route: immune cells move across endothelial walls using these gaps

e.g. distance between each cell is bigger to neutrophils can cross

image: reg. of integrins/adhesion molecules by inflam, factors

SUMMARY: reg. of integrins/adhesion molecules by inflam, factors

• vasoactive mediators slow down local flow

• leukocytes adhere and roll over the vascular wall:

  • first contact via selectins, rolling via integrins

• circulating leukocytes in local capillaries come near vascular walls and sense chemokines

• cytokines, chemokines and PGs stimulate expression or strengthen binding of adhesion molecules (vascular endothelium) and integrins (immune cells)

• adhered leukocytes crawl over the vascular wall. adherent interactions become tighter

• histamine, PGs and adherent binding relaxes connections between adjacent vascular endothelial cells. Oedema is facilitated

• leukocytes move between vascular endothelial cells and into tissues: diapedesis

summary image

oedema

swelling/build up of fluid in a body tissue

cadherin

cell adhesion molecules important in forming adherens junctions that let cells adhere to each other

depend on Ca ions to function

leukocytes/IICs

leukocytes aka IICs

Q: proteins expressed on the leukocyte are ___

integrins

Q: proteins expressed on endothelium are ____

selectins

Q: this leukocyte stimulates gaps between endothelial cells via ____

tethering to adhesion molecules

Q: the 2 main types of vasoactive mediators are ___

histamine & PGs

Q: the mediators that attract the monocytes are ___

chemokines

recirculation of DCs

• recogn. of PAMPs and exposure to cytokines at sites of infection trigger phagocytosis and Ag processing in DCs

• leads to DC maturation

• mature DCs migrate to nearby lymph nodes where they ‘educate/train’ the AIS

• migration is coordinated by CCL21 released from lymphatic endothelium

• DCs sense this via CCR7 receptor and migrate towards lymph nodes

inflammation

a natural response of our organism against injury or infection that helps clear pathogens and promotes tissue repair

chronic inflammation

a deleterious response whereby excessive or sustained activation of the IS causes tissue destruction or abnormal repair. Self-perpetuatingauto

autoimmune disease

disease where certain components of the IS actively attack host tissues

part 1. physiologic inflammation and tissue repair

• epithelial barrier is breached - PAMPs and DAMPs sensed

• resident ICs release early mediators: chemokines ( circulating ICs attached), histamine and PGs (vasodilation, slower blood flow)

• cytokines/chemokines: induction of selectins/adhesion molecules (vascular endothelium), Ag presentation (local)

• infiltration of monocytes: degranulation and bacterial killing

  • DCs, Ag capture, presentation and recirculation

part 2. physiologic inflammation and tissue repair

• infection is cleared

• granulocytes have mostly been destroyed during bacterial killing

• monocytes and DCs may recirculate

• remaining and resident MPs stimulate healing

• stromal cells, such as fibroblasts are activated to prod extracellular matric to restore the basal membrane

• epithelial cells are regenerated to repair the normal tissue architecture

phase 1 physiological image

phase 2 physiological image

phase 1. pathologic inflammation: tissue destruction or scarring

• persistent activation of IICs. Can be triggered by:

  • genetic defects (e.g. NOD2 muts. in IBD)

  • loss of tolerance towards commensal microbes

  • defective epithelial barriers

  • abnormal adaptive immunity (e.g. autoantibodies)

• continuous or enhanced recruitment of granulocytes: degranulation leads to epithelial damage

• accum. of MPs with enhanced prod. of cytokines causing further activation of other immune and structural cells

• MP prods can also damage epithelium

• AICs also recruited and activated, incr. cytokine prod

phase 2. pathologic inflammation: tissue destruction or scarring

• local structures such as fibroblasts are overactivated

• incr. motility of fibroblasts leads to tissue accum.

• in part due to constant activation fro MP-derived prods (transforming growth factor-beta1)

• overprod. and deposition of ECM may lead to fibrosis and tissue strictures

• or excess damage of epithelial wall can cause ulcerations or fistulas

• in most patients w/ chron. inflam. D this abnorm. tissue remodelling is ultimate cause of severe disease = surgery (often)

phase 1 pathological image

phase 2 pathological image