Antigen Presentation and Lymphocyte Activation

Antigen Presentation and Lymphocyte Activation

The peripheral lymphoid organs are the primary meeting place between cells of the innate immune system (APCs) and cells of the adaptive immune system (T-cells and B-cells). Upon interaction with APCs, pathogen-specific T-cells and B-cells will be activated, provided that they acquire the appropriate signals from the APCs. Besides require co-stimulatory signals via interaction of accessory and co-stimulatory molecules between lymphocytes and APCs. This cell-cell interaction is essential for proper stimulation of lymphocytes and without those accessory signals, antigen-specific T-cells may become anergic. Lymphocytes receiving the appropriate signals for activation will clonally expand and generate multiple progenitors all recog-nizing the same antigen. Clonalexpansion is a typical feature of the adaptive immune system, which will be discussed in more detail below.