Binding of a soluble p70 killer cell inhibitory receptor to HLA‐B*5101: Requirement for all three p70 immunoglobulin domains

Lysis of target cells by natural killer (NK) cells can be prevented by killer cell inhibitory receptors (KIR) specific for major histocompatibility complex class I molecules. Functional studies have identified two distinct p58 KIR, each reactive with a different group of HLA-C allotypes, and distinct p70 KIR specific for some HLA-B or HLA-A allotypes. The NK specificities for each group of HLA-C allotypes have been reproduced by direct binding of recombinant soluble p58 molecules. Here, we show that a soluble p70 KIR binds to HLA-B*5101, but not to HLA-A or HLA-C molecules. Truncated soluble forms of the HLA-B*5101-specific p70 KIR, including one with two immunoglobulin (Ig) domains reactive with a monoclonal antibody that blocks p70 KIR function, did not bind to HLA-B*5101, indicating that all three Ig domains are required for binding.