KIR3DL1 and preeclampsia: Based on the predominance of these activating or inhibitory KIRs, two primary KIR haplotypes have been defined: KIR A and KIR B. The KIR A haplotype is characterized by a predominance of inhibitory KIRs such as KIR2DL1, KIR2DL3, and KIR3DL1; it is associated with stronger inhibitory signals that promote immune tolerance, but may also be linked to complications in pregnancy, such as preeclampsia, due to insufficient uNK cell activation and poor trophoblast invasion.