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. Author manuscript; available in PMC: 2011 Sep 17.
Published in final edited form as: Cell. 2010 Sep 17;142(6):847–856. doi: 10.1016/j.cell.2010.08.031

Figure 1. Evolutionary Origins of Non-autoreactive Activating Receptors.

Figure 1

(A) New activating receptors for natural killer cells are generated by duplication of an inhibitory receptor gene and the subsequent conversion to an activating receptor. This conversion occurs when the codons for the transmembrane (TM) and intracellular domains are exchanged with those of an activating receptor by crossover events. If the new activating receptor is specific for self-major histocompatibility complex (MHC) class I, it might cause autoimmunity and be selected against. (B) Inhibitory receptors that are specific for both MHC class I and pathogen-encoded ligands have also been converted to activating receptors. Subsequent mutations have eliminated the specificity for MHC class I and retained specificity for the pathogen-encoded ligand.