Natural Killer (NK) Cells in Hamsters and Their Modulation in Tumorigenesis

Natural killer (NK) cells have been reported in several species including mice, rats, hamsters, guinea pigs, miniature swine, chickens and humans (1–14). These normal unsensitized lymphocytes exhibit cytolytic activity against a variety of targets including tumors and virus-infected cells (15–18). NK cells that have been studied extensively in mice and humans are small, non-adherent, non-phagocytic lymphocytes that originate in the bone marrow (14,19–22). NK cells lack conventional levels of T- and B-cell surface markers. Human NK cells have readily detectable Fc receptors on their surface, whereas mouse NK cells may express only low concentrations of Fc receptor, which are difficult to demonstrate (23). Recently it has been shown that NK cells of both mice and humans may have a low level of T-cell markers such as theta antigen and E rosette receptors, respectively (24,25). NK-cell activity is age-related (1,2) and genetically controlled (26, 27).