Blood Cells - Tissue Functioning and Remodeling in the Circulatory and Ventilatory Systems - page 128

Table 3.28. Adhesion molecules and chemokine receptors in peripheral memory T-cell migration
(Source: [ 235 ]; CCL: CC-chemokine ligand; CCR: CC-chemokine receptor; CLA: cutaneous
lymphocyte-associated antigen; ICAM1: intercellular adhesion molecule-1; MADCAM1: mucosal
vascular addressin cell adhesion molecule 1; PNAd: peripheral lymph node addressin; VCAM1:
vascular cell adhesion molecule 1).

Molecule Receptor Tissue tropism

CD44 Hyaluronate and fibrinogen General

CD43 E-selectin General

Integrin- α L β ICAM1 General 2

P- and E-selectin ligands P- and E-selectin General

Integrin- α β VCAM1 and fibronectin General 4 1

Integrin- α β Collagen and laminin Lung airways 1 1

L-selectin PNAd Lymph node

CCR7 CCL19 and CCL21 Lymph node

CLA-modified ligands E-selectin Skin

CCR4 CCL17 Skin

CCR10 CCL27 and CCL28 Skin

Integrin- α 4 β 7 MADCAM1 Gut

CCR9 CCL25 Small bowel

3.10.4.5 Regulatory T Lymphocytes

+

CD4 regulatory T cells (T Reg ) are immunosuppressive lymphocytes that permit

immunological tolerance. They maintain self tissue tolerance to avoid autoimmunity
and allow fetomaternal tolerance. Pregnant women are indeed able to allow the
growth during 9 months of fetuses that are antigenically foreign bodies.
Fetal and adult T cells arise from different populations of hematopoietic stem
cells. The human fetal T-cell compartment begins to develop at approximately
gestational week 10. The majority of fetal T cells at mid-gestation (

∼

16-24
gestational wk) have a surface phenotype comparable to that of conventional naive
T cells in neonates and adults [ 237 ]. In particular, many 18-to-22-wk-old fetal
CD4

+ +

T cells of mesenteric lymph nodes many have a phenotype (PTPRc ,

+ − α − +

CCR7 T cells. The

fetal T-cell lineage is directed toward immune tolerance. Tolerance in the human
fetus is partly mediated by an abundant population of fetal regulatory T cells. The
developing human fetus actually possesses a greater percentage (

, TNFRSF6 ,IL2R ) similar to that of naive adult CD4

∼

15%) of total

+ ∼

peripheral CD4 T cells than that in healthy infants and adults ( 5%) [ 237 ]. Fetal

+

naive CD4 T cells are much more responsive than adult naive T cells to allogeneic

cells [ 237 ]. Unlike adult T cells, fetal T cells have an enhanced proliferation rate
after exposure to maternal alloantigens. This T-cell pool gives rise to T Reg cells
upon stimulation. This process depends on transforming growth factor

β

. Hence, in
humans, fetal exposure to foreign antigens, notably maternal alloantigens, can lead
to the generation of immune tolerance.
T Reg cells also contribute to the maintenance of a balance with commensal
microbial flora. They participate in the regulation of immune responses to pathogens