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290 ParT TwO Host Defense Mechanisms and Inflammation

Naïve T and B cells Memory T and B cells
CD45RA + CD45RO +
L-Selectin + L-Selectin -
+ +++
α 4 β 7 α 4 β 7
LFA-1 + LFA-1 ++

HEV MLV TD Blood stream
Effector sites
GALT High endothelial venule
Lymphocyte receptor HEV ligand Steps in homing
+
α 4 β 7 MAdCAM-1 A. Rolling
L-Selectin + L-Selectin-
LFA-1 + ICAMs MAdCAM-1
SLC (6 C-kine, Exodus-2) CCR7 B. Binding/activation
α 4 β 7 -MAdCAM-1
SLC-CCR7
C. Arrest
α 4 β 7 -MAdCAM-1
LFA-1-ICAMS
Cuboidal endothelial cells
A D. Diapedesis
Inductive sites

Memory T and B cells
CD45RO +
L-Selectin -
+++
α 4β 7
LFA-1 ++
LEV: Lamina propria endothelial venule
Lymphocyte receptor Lamina propria ligand Steps in homing
+++
α 4 β 7 MAdCAM-1 A. Rolling
LFA-1 ++ ICAMs α 4 β 7 -MAdCAM-1
G protein-coupled TECK B. Binding/activation
receptor-9-6 (CCR-9) α 4 β 7 -MAdCAM-1
CCR9-TECK
C. Arrest
α 4 β 7 -MAdCAM-1
LFA-1-ICAMS
B Cuboidal endothelial cells D. Diapedesis
FIG 20.5 Structural Features and Lymphocyte Homing to Gut-Associated Lymphoreticular
Tissues (GALTs). (A) High endothelial venules (HEVs) occur in T-cell areas and express the
ligands mucosal addressin cell adhesion molecule-1 (MAdCAM-1), intercellular adhesion molecule
+
+
1 (ICAM-1), and CCR7. Naïve T and B cells, which are L-selectin , α 4β 7 , and leukocyte function–
+
associated antigen-1 (LFA-1) , all participate in rolling, binding activation, arrest, and diapedesis
in the HEV. Memory B and T cells express α 4β 7 and LFA-1 at a higher level. (B) Lymphocyte
receptors and addressin ligands involved in homing to mucosal effector sites of the gastrointestinal
(GI) tract. The majority of B and T cells exhibit a memory phenotype with coexpression of high
levels of α 4β 7 and LFA-1. The expression of the G-protein–coupled receptor CCR9 allows the
homing steps that occur on lamina propria venules.

further refinement, with evidence that migration of cells into cell adhesion molecule-1 (MAdCAM-1) is the most important
and from NALTs follows rules different from those for GALTs addressin expressed by PP HEVs or lamina propria venules (LPVs).
and the GI tract. PNAd and vascular cell adhesion molecule 1 (VCAM-1) are the
principal addressins expressed by peripheral lymph node and
Lymphocyte Homing in the GI Tract skin HEVs, respectively (Chapter 11).
Naïve lymphocytes enter mucosal or systemic lymphoid tissues Integrins are a large class of homing receptors character-
from blood through specialized HEVs (Fig. 20.5A) (Chapter 11). ized by heterodimeric α and β chains (Chapter 11). In general,
14
In GALTs, HEVs are present in the interfollicular T-cell zones. the β 1 integrin characterizes the homing receptor for skin,
In effector sites, such as the lamina propria of the gut, the HEVs whereas the β 7 integrin characterizes the receptor for the gut.
tend to occur near villi crypts (see Fig. 20.5B). Mucosal addressin The pairing of α 4 with β 7 is thus responsible for lymphocyte