Figure 1. General Principles of Antigen Recognition by the Adaptive Immune System.
Upon stimulation, B lymphocytes differentiate into plasma cells (left panel) to produce antibodies (immunoglobulins). These can bind to a variety of intact proteins (but also other molecules) that are exposed on the cell surface. The antigen-binding portions of an antibody are composed of variable light (VL) and variable heavy chain (VH) domains (insert). CAR T cells (middle panel) recognize the same types of molecules as do the antibodies. These cells have been modified to express CARs, which are constructed by fusing antibody-derived antigen-binding domains (VH + VL) with intracellular T cell signaling domains (insert). In contrast, conventional T cells (right panel) recognize peptides that are derived from cellular proteins and are displayed on cell surface in complex with MHC molecules. For clarity, only the presentation on MHC class I molecules is depicted, in a simplified manner.