Test Details: Natural Killer (NK) cell function is modulated by multiple cell surface receptors including Killer immunoglobulin-like receptor (KIR). There are multiple KIR genes (inhibitory or activated), which are various in number and/or composition among individuals on chromosome 19q. Combination of KIR genes affects NK cell function and is associated with the risk of development of certain types of cancers, viral infections and collagen disease. In Hematopoietic stem cell transplants (HSCT), KIR-ligand mismatch in the graft-versus-host (GvH) direction occurs when the recipient lacks one or more major KIR-ligands.