Publisher Summary NK cells have been identified in many vertebrate species and have
been operationally defined as cells capable of mediating spontaneous in vitro cytotoxicity
against a variety of target cell populations without apparent prior sensitization. NK cells have
been considered distinct from specific cytotoxic T lymphocytes (CTL) because they do not
have clonally distributed specificity, restriction for products of the major histocompatibility
complex (MHC) at the target cell level or immunologic memory. Despite this apparent lack of …