MEDSCI 708

Cell Adhesion and leukocyte trafficking - Geoff Krissansen

For additional detail please refer to lecture notes handout.Partly taken from http://hsc.virginia.edu/medicine/basic-sci/biomed/ley/index.html, R&D Systems, Springer TA Annu Rev Physiol 57: 827-872, 1995, Bochner BS J Allergy Clin Immunol 106: 817-828, 2000,and and Salmi M and Jalkanen S Nature Rev Immunol 5: 760771, 2005; http://www.cbr.med.harvard.edu/labs/springer/lab_goodies/lab_goodies.html

Cells

Extracellular matrix

Glycosaminoglycans form proteoglycans hydrated gel-like substance

Fibrous proteins: Structural eg collagen and elastinAdhesive eg fibronectin and laminin

The extracellular matrix provides connective tissue and a roadway

Ligand subunit subunit

-propeller

EGF-like cysteine-rich repeats

Transmembrane domain

Ca++Ca++

Ca++

MIDAS

I-domain

MIDAS

Ligand subunit subunit

-propeller

EGF-like cysteine-rich repeats

Post-translational cleavage

Transmembrane

domain

Ca++Ca++

Ca++

*MIDAS

Ca++

Integrins

Inactive Active From Cell, 110, Takagi J, Petre BM, Walz T, Springer TA

Table 1. Leukocyte integrins and their ligands

L2

Leukocytes

ICAM-1, ICAM-2, ICAM-3

Telencephalin, Type I collagen

Landsteiner-Wiener (LW) blood

group glycoprotein

M2 Leukocytes ICAM-1, iC3b, factor X, galectin-3, Cfibrinogen

complement factor H, CD23,

neutrophil inhibitory factor,

oligodeoxynucleotides,

heparin, elastase, -glucans,

high molecular weight kininogen,

myeloperoxidase, azurocidin,

haptoglobin, denatured proteins,

Landsteiner-Wiener (LW) blood

group glycoprotein, fibrinogen,

Lipopolysaccarides, pertussis toxin

X2 Leukocytes iC3b, fibrinogen, CD23, ICAM-1

lipopolysaccarides

D2 Macrophages, eosinophils (esp tissue cells eg foam cells)

ICAM-3, VCAM-1

41 Leukocyte, muscle,

VCAM-1, FN, MAdCAM-1

stimulated neutrophils,

TSP, osteopontin, chondroitin

neural crest cells,

sulfate glycosaminoglycan

fibroblasts

Propolypeptide of von Willebrand factor

casein, denatured albumin, 4 subunit

47 Leukocytes MAdCAM-1 (eg on HEV),VCAM-1, FN

E7 Activated leukocytes, IEL E-cadherin, RGD proteins?

2

On villi

7Deficiencyimpaired mucosal immunity

Deficiency LAD-1

Deficiency Reduced mast cells in peritoneum and skin

Integrin ligands- Ig CAMs

ICAM-3CD50

LFA-1

Leukocytes activated resting activated HEV endothelium endothelium endothelium activated leuk resting lymph/mono macrophage

L-selectin

P-selectin

E-selectin

Mucins

Selectins

On tips of villi

Selectin KO micereveal individual roles

On tips of villi

endomucinpodocalyxin

The multistep process of leukocyte extravasation

Margination

Luster et al. Nature Immunology 6: 1182-1190, 2005

Ectoenzymes help control leukocyte traffic

Ectoenzymes include proteases, nucleotidases, and oxidases

Nucleotidases:

ATP is proinfammatory: ATP binds purinergic receptors of the P2X abd P2Y families, and induces proliferation by inducing cytokine expression, and activating dendritic cells.

Adenosine is anti-infammatory: Adenosine prevents leukocyte activation- inhibits L-selectin shedding and expression of CD18 integrins, and down-regulates VCAM-1 and cytokine expression by endothelial cells.

CD73: is a cell surface molecule expressed by vascular endothelial cells and up to 15% of lymphocytes (but not by granulocytes and monocytes). It catalyses the dephosphorylation of AMP to adenosine. Mice deficient in CD73 show increased leukocyte attachment to the endothelium, and leukocyte migration.

CD39: converts extracellular ATP to AMP, and is expressed by many different types of leukocytes, and by vascular endothelial cells. Mice deficient in CD39 display exacerbated skin inflammation by irritants.

The balance of ATP-generating and ATP-consuming pathways on the surfaces of leukocytes and endothelial cells influences the local inflammatory environment.

ATP is dephosphorylated to AMP by CD39 on resting endothelium, and AMP is dephosphorylated to adenosine by CD73, creating an anti-inflammatory setting. The activity of CD73 is inhibited when lymphocytes by the endothelium, which leads to increased leukocyte migration.

ADP-ribosyltransferases:ADP-ribosyltransferases such as ART2 transfer the ADP-ribose moiety from NAD(P) to an acceptor. The ADP-ribose moiety can covalently modify and inactivate several surface proteins including L2.

Ectopeptidases regulate chemokinesCD26 is an ectoenzyme that cleaves N-terminal dipeptides and is expressed de novo on activated T and B cells, NK cells, and endothelial cells. Cleavage of chemokines by CD26 reduces their ability to bind and activate chemokine receptors, whereas their ability to serve as chemoattracts can be enhanced (eg CCL5). Rodents that are deficient in CD26 have increased infiltration of leukocytes into the lung and joints in models of asthma and arthritis, suggesting that CD26 plays a role in inhibiting inflammation.

SheddasesCD156b is a sheddase that cleaves L-selectin from the surface of thymocytes. Other sheddases are also involved. L-selectin is shed from lymphocytes to prevent re-entry of activated T cells to secondary lymphoid organs.

Ectoenzymes in the control of leukocyte traffic

Poorly characterized

Table 1 Receptors on leukocytes that contribute to selective cell recruitment Leukocyte surface structure Ligands Pattern of leukocyte expression

Adhesion molecules

L-selectin PNAd, others All leukocytes, but naive T cells > memory T cells

PSGL-1 P-selectin All leukocytes, but eosinophils > neutrophils

CLA E-selectin Skin-homing memory T cells

Sialyl-dimeric Lex E-selectin All leukocytes, but neutrophils > eosinophils

41 integrin VCAM-1, others All leukocytes except neutrophils

47 integrin MAdCAM-1, others All leukocytes except neutrophils

E7 integrin E-cadherin Intraepithelial lymphocytes

Chemokine receptors

CCR3 Eotaxin 1-3, others Eosinophils, basophils, mast cells; some TH2 cells

CCR4 TARC, MDC Skin-homing memory T cells

CCR5 MIP-1 TH1 cells

CCR6 MIP-3 Memory T cells

CCR7 SLC (CCL21), Naive B and T cells

MIP-3 (CCL19)

CCR8 I-309 TH2 cells

CCR9 TECK Gut-homing memory T cells

CCR10 CTACK Skin-homing memory T cells

CXCR3 Mig, IP-10, I-TAC TH1 cells

CXCR5 BLC (CXCL13) Naive B cells

PNAd, Peripheral lymph node addressin; PSGL-1, P-selectin glycoprotein ligand-1; CLA, cutaneous lymphocyte antigen; Lex, Lewis X; VCAM-1, vascular cell adhesion molecule-1; MAdCAM-1, mucosal addressin adhesion molecule-1; TARC, thymus- and activation-related chemokine; MDC, macrophage-derived chemokine; MIP, macrophage inflammatory protein; SLC, secondary lymphoid tissue chemokine; TECK, thymus-expressed chemokine.

Trafficking of leukocytes to specific organs and tissues

Serves to:

1) Increase the efficiency of regional immune responses.

2) Allows functional immune specialization of particular tissues.

Differences in chemokine receptor, integrin, or selectin expression plays a major role in selective leukocyte recruitment –allows for multiple choices.

Chemokines are key factors in the development and maintenance ofsegregated microenvironments characteristic of secondary lymphoid organs.

Homing of lymphocytes to lymph nodes

Balanced responsiveness to chemokines determines B cell entry into B and T cell zones

From Reif et al. Nature 416: 94-99, 2002

CCL19 = MIP3CCL21 = SLCCXCL13 = BLC

T cell zone B cell zone (follicle)

B cell zone stromal cell

T cell zone stromal cell

CXCR5

CCR7

BLC

MIP3, SLC

Homing of memory T cells and eosinophils to skin

Leukocyte homing to the gut

Key points often overlooked

•Only lymphocytes are capable of recirculating- neutrophils don’t recirculate

• 4 integrins are expressed on the microvillus tips of lymphocytes and assist with lymphocyte tethering

•Chemokines are presented to leukocytes by heparan sulfate on the lumenal surface of the vascular endothelium

•Tissue restricted recirculation of memory and effector lymphocytes serves to increase the efficiency of regional immune responses, and allow functional specialization of particular tissues