Abstract
The cell-adhesion molecule L1 was originally described in the nervous system. It has recently been detected in CD4+ T lymphocytes, peripheral B lymphocytes, and granulocytes in the human immune system and in similar leucocyte types in the murine immune system. L mediates neural recognition by Ca+2, Mg+2-independent homophilic binding. In the human and murine immune systems, L1 binds to the “classical” vitronectin receptor, αVβ3, and fibronectin receptor, α5β1, respectively, and abstains from homophilic binding. Homophilic L1 binding probably involves antiparallel alignment of several interactive domains. Integrin binding is mediated by a short segment of immunoglobulinlike domain 6, which includes two RGD repeats in rodent L1 and one RGD motif in human L1. L1 is modulated in activated leucocytes in vitro in parallel to L-selectin, and diverse cell types release intact L in vivo and in vitro. Released L1 can bind to laminin and adheres to the extracellular matrix of sciatic nerve, M21 melanoma, and possibly spleen and other tissues. It can support integrin-dependent cell migration and preliminary data implicate it in tumor development and transnodal lymphocyte migration.
Highlights
The development of a functional cellular immune system and effective immune response depends on selective leucocyte trafficking to, from, and within organs of the immune system as well as to variable but specific addresses such as inflammatory sites.Correct leucocyte trafficking is mediated by contactdependent interactions between leucocytes and postcapillary endothelial cells, glandular stroma cells, and extracellular matrices
L1 is primarily expressed by neural and blood cells involved in targeted migration and is at present the only known cell-adhesion molecule that is abundant in both nervous and immune systems
Its function(s) in the immune system is not certain, but preliminary studies using tumor lines, T and B lymphoblasts suggest that L1 may be involved in both leucocyte-leucocyte and leucocyte-endothelial cell interactions
Summary
The development of a functional cellular immune system and effective immune response depends on selective leucocyte trafficking to, from, and within organs of the immune system as well as to variable but specific addresses such as inflammatory sites. Correct leucocyte trafficking is mediated by contactdependent interactions between leucocytes and postcapillary endothelial cells, glandular stroma cells, and extracellular matrices These interactions require multiple-adhesion mechanisms that can recognize appropriate targets and be modulated by the cell during recognition events. L1 is primarily expressed by neural and blood cells involved in targeted migration and is at present the only known cell-adhesion molecule that is abundant in both nervous and immune systems. L1 is predominantly expressed by neuronal subsets and Schwann cells It mediates neuronal adhesion, axonal navigation and fasciculation, axon-Schwann cell recognition, and possibly granule-cell migration. Its function(s) in the immune system is not certain, but preliminary studies using tumor lines, T and B lymphoblasts suggest that L1 may be involved in both leucocyte-leucocyte and leucocyte-endothelial cell interactions.
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