The PK136 antibody is specific for mouse NK1.1, a type II transmembrane lectin-like receptor and member of the killer cell lectin-like receptor (KLR) family. NK1.1 is prominently expressed on natural killer (NK) cells, and is correlated with NK cytotoxic effects toward virus-infected cells and tumor cells. NK1.1 is expressed on subsets of NKT cells in certain mouse strains (C57BL/6, FVB/N, and NZB), yet absent from others (AKR, BALB/c, CBA/J, C3H, DBA/1, DBA/2, NOD, SJL, and 129). Putative subsets of NK cells and their expression of NK1.1 antigen are of continuing interest, including NK1.1+/CD117+ (c-Kit) cells reported to be immunosuppressive for CD8+ T cells in a mechanism involving PD-1 and PD-L1. The PK136 antibody may be used for detection of NK1.1 expression on mouse strains including CE, B6, NZB, C58, Ma/My, ST, SJL, and FVB. The antibody is reported to react with an epitope common to NKR-P1B and NKR-P1C alloantigenic forms of NK1.1.