The PK136 monoclonal antibody is specific for the mouse NK1.1, a receptor from the killer cell lectin-like receptor (KLR) family. Nk1.1 is an antigen encoded by the Klrb1c/NKR-P1C gene expressed by the natural killer cells of some selected strains of mice (C57BL, FVB/N, NZB) and encoded by the Klrb1b/NKR-P1B gene expressed on Swiss NIH and SJL mice. Pk136 binds to an epitope common to NKR-P1B and NKR-P1C.

The Klrb1 is a family of type II transmembrane C-type lectin receptors. Klrb1c activates the NK-cell cytotoxicity, while Klrb1b inhibits it.

PK136 is useful in defining the NK cells and the rare population of NK-T lymphocytes and specific cultured monocytes.