Natural killer (NK) cells are a subset of lymphocytes responsible for killing infected or abnormal cells through the release of cytotoxic granules and production of cytokines. NK cell activity is tightly regulated by interactions between killer-cell immunoglobulin-like receptors (KIRs) on the NK cell surface and HLA Class I alleles on target cells. KIRs may be either inhibitory or activating, and the balance of these signals determines NK cell activation.

The KIR gene locus is polymorphic and highly homologous, located on chromosome 19q13.4 within the leukocyte receptor complex. Human NK cells express various combinations of 16 KIR genes, organized into two common haplotypes:

• Group A: Enriched in inhibitory receptors
• Group B: Enriched in activating receptors

Recent studies have shown that specific combinations of maternal KIR genotypes and parental HLA-C genotypes are associated with recurrent spontaneous abortion.

• Clotted samples
• Specimens not collected in EDTA tubes
• Frozen specimens

Polymerase Chain Reaction (PCR).

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