KLRK1 and classic Hodgkin lymphoma: The paucity of NK cells in the reactive infiltrate of cHL and the systemic NK cell deficiency observed in cHL patients prompted further investigation into the immune-modulatory mechanisms of NK receptors such as the NKG2D activating receptor of the C-type lectin superfamily, killer immunoglobulin-like receptors (KIRs), immunoglobulin-like transcript 2 (ILT2) inhibitory receptors, immunoglobulin-like transcript 4 (ILT4) and the NKG2A inhibitory receptor.