Natural killer cells: artifact to reality: an odyssey in biology.

The biology of the natural killer cell system is being investigated by many different laboratories using multiple approaches. The rationale for these investigations is the experimental evidence that NK cells play some role in inhibiting tumor growth and metastasis, convey some protective immunity and may be operative in control of differentiation from fetal life to adulthood. Thus, a survey of the literature reveals a multiplicity of studies examining many of these potential roles for NK cells. This review will attempt to summarize some of the findings critical to an understanding of the role NK cells play in immunophysiology and in immune reactions to various diseases. Even after ten years of study, the whole system of 'natural' reactivity remains difficult to define. The evidence available would indicate that the NK system while incompletely understood, may be manipulated in favor of the host when threatened by infectious or neoplastic disorders.