Expert Reviews in Molecular Medicine:
Accession information: (00)001733h.htm (shortcode: fig005hka); 19 April 2000
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Schematic representation of the co-stimulation of CD8+ T cells

Heidi Hörig, Freddy A. Medina, William A. Conkright and Howard L. Kaufman

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Figure 5. Schematic representation of the co-stimulation of CD8+ T cells. (a) The first activating signal (‘signal 1’) is delivered to the T-cell receptor by the complex formed between a major histocompatibility complex (MHC) molecule (MHC class I is shown here) and a peptide derived from an antigen [such as the tumour antigen carcinoembryonic antigen (CEA)]. (b) A second signal is delivered when B7 (CD80) molecules expressed on the (professional) antigen-presenting cell (APC; or tumour cell) bind to CD28 on the T cell. (a) If only the first signal is received, T-cell unresponsiveness occurs (i.e. T cells are not activated sufficiently for tumour cells to be lysed). (b) If both signals are received, the T cell becomes activated and tumours can be targeted and lysed by the CD8+ cytotoxic T cells. However, the expression of B7 molecules is often reduced on tumour cells, and this might be one of the ways by which these cells escape T-cell recognition (fig005hka).

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