Figure 2. NK cell education and recognition of allogeneic paternal MHC molecules on trophoblast cells.
Individuals inherit one KIR haplotype on chromosome 19 from each parent. Each haplotype contains 7–15 genes (only a few are depicted here for clarity). During NK cell differentiation, KIR genes are expressed in developing NK cells. Each NK cell expresses 0–5 KIRs. Some of the KIRs bind to self MHC molecules and educate NK cells to be tolerant of self and also to react to the absence of self. Allogeneic, paternal MHC molecules on the trophoblast cell can interact with some KIRs on the uNK cell; however, it is not known whether this new interaction educates uNK cells or if the uNK cells recognize the paternal, allogeneic MHC molecule as foreign, generating an alloresponse.