Activation of human NKCC by moderate exercise: increased frequency of NK cells with enhanced capability of effector--target lytic interactions.

In the present study we examined the mechanism of human natural killer cellular cytotoxicity (NKCC) augmentation by 5 min of moderate exercise and its interrelationship to in vitro interferon (IFN) activation. Cytotoxicity was measured by employing both a single-cell cytotoxic assay and a standard 3-hr chromium-51 (51Cr) release assay. The former was used to assess changes at the single NK cell--target cell level and the latter to assess changes in overall lytic capacity of a given population of NK cells. Several findings were obtained: (1) moderate exercise augmented NKCC in vivo by recruiting a 'new' population of active cytotoxic NK cells. (2) This 'new' population of active cells probably was derived from cells which can bind targets but are non-cytotoxic. (3) In a standard 51Cr-release assay, additional augmentation of these exercise-activated cells occurred in vitro following exposure to interferon. (4) This additional increase in cytotoxicity produced no alteration in the frequency of killer cells as viewed at the single cell level. (5) Thus interferon's capacity to increase further the overall lytic ability of exercise-activated NK cells was not due to its activation of an additional subset of pre-NK cells, but due to its increasing the capacity of effector--target lytic interactions (recycling) of the same set of NK and pre-NK cells.