Xenbase Image ID: 174570

Fig. 2. Schematic overview of a typical mammalian adaptive immune response. Productive T-cell activation requires two signals from an APC (e.g., dendritic cells, macrophages): the first signal is due to the recognition by the TCR of the MHC molecules complexed with the antigenic peptide (CD4 T cells interact with class II molecules, CD8 T cells with class I molecules), the second signal is provided by costimulatory molecules (e.g., B-7, CD40) that are up-regulated following APC activation by pathogen products or PAMPs binding to PRRs such as TLRs. Activated T cells proliferate and differentiate into cell effectors: CTLs able to kill target expressing the same Ags-class I complex and CD4 T helper cells producing various cytokines that act on the pathogen as well as on other immune cells including CD8 T and B cells. Most T cells die from apoptosis after the response (contraction phase), except a long-lived minor population of memory T cells able to respond faster to a second pathogen exposure. For abbreviations, see list. [APC= antigen presenting cell; Ag =Antigen] Image published in: Robert J and Ohta Y (2009) Copyright © 2009. Image reproduced with permission of the Publisher, John Wiley & Sons. Larger Image Printer Friendly View

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