Reference values for relative numbers of natural killer cells in cattle blood.

Natural killer (NK) cells have been studied in humans and rodents for almost 30 years, but little is known about NK cells in other mammals, such as cattle. Recently, a monoclonal antibody directed against bovine NKp46, a receptor that is expressed exclusively on NK cells, was developed. We have utilized this antibody to study the relative numbers of NK cells in blood of 254 cattle at different ages. The highest relative number of NK cells was observed in young calves, and gradually decreased with age to a bottom level in heifers, followed by a moderate increase in adults. Relative numbers of NK cells in cattle were generally lower than in humans, but age-related changes in bovine NK cells showed similar tendencies as reported in humans. The present material provides a source for reference values for NK cells in cattle at various ages.