Figure 1. The emergence of NK cells from obscurity to biological prominence.

(A) When discovered in the 1980s, NK cells were recognized as CD45⁺CD56⁺CD16⁺ effector lymphocytes that did not express the T cell receptor or the B cell receptor. (B) Today, the NK cell surface is decorated by multiple receptors, only some of which are shown above. Sixteen activating proteins (NCRs, green), at least ten different KIRs, and various inhibitory receptors such as NKG2D or TRAIL (red), chemokine receptors (e.g., CXCR3 or CXCR4) and cytokine receptors (including IL-2R and IL-15R, blue), and adhesion molecules (e.g., DNAM-1, yellow) are expressed on NK cells. Further, NK cells produce a variety of cytokines and soluble factors that modulate functions of cells interacting with NK cells. NK cell–associated receptors and ligands are reported with regular frequency, as functionally diverse subsets of trNK cells are discovered and characterized. The study by Yang, Neo, and colleagues (11) reports that Trx1 content increases in activated NK cells and that the levels of thiols (purple) are upregulated on the cell surface, providing a protective screen against ROS.