CD2 and the integrin LFA-1 are cell-adhesion molecules on the surfaces of T cells that bind, respectively, to LFA-3 and ICAMs (intracellular cell-adhesion molecules) on antigen-presenting cells and various target cells (see Figure 9-13). The level of LFA-1 and CD2 is twofold to fourfold higher on effector T cells than on naive T cells, enabling the effector T cells to bind more effectively to antigen-presenting cells and to various target cells that express low levels of ICAMs or LFA-3.
As Chapter 9 showed, the initial interaction of an effector T cell with an antigen-presenting cell or target cell is weak, allowing the TCR to scan the membrane for specific peptides
Comparison of naive and effector T cells
Naive T cells
Effector T cells
Co-stimulatory signal (CD28-B7 interaction) CD45 isoform
Cell-adhesion molecules (CD2 and LFA-1) Trafficking patterns
Required for activation
HEVs* in secondary lymphoid tissue
Not required for activation
Tertiary lymphoid tissues; inflammatory sites
Effector molecules produced by effector T cells
Cytotoxins (perforins and granzymes), IFN-7, TNF-p IL-2, IL-3, TNF-p, IFN-7, GM-CSF (high) IL-3, IL-4, IL-5, IL-6, IL-10, IL-13, GM-CSF (low)
Fas ligand (FASL)
CD40 ligand presented by self-MHC molecules. If no peptide-MHC complex is recognized by the effector cell, it will disengage from the APC or target cell. Recognition of a peptide-MHC complex by the TCR, however, produces a signal that increases the affinity of LFA-1 for ICAMs on the APC or target-cell membrane, prolonging the interaction between the cells. For example, TH1 effector cells remain bound to macrophages that display peptide-class II MHC complexes; TH2 effector cells remain bound to B cells that display peptide-class II MHC complexes; and CTL effector cells bind tightly to virus-infected target cells that display peptide-class I MHC complexes.
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.