Role of macrophage in in vitro augmentation of rat, mouse, and human natural killer activities.

Requirement for macrophages in in vitro augmentation, by interferon (IFN), polyinosinic-polycytidylic acid (poly I:C), or Corynebacterium parvum, of rat, mouse, and human natural killer (NK) activities was examined. Several differences were seen among the species. Mouse NK activity demonstrated some lability at 37 degrees C and a strict macrophage requirement for in vitro production of IFN, and augmentation of NK activity was demonstrated by either poly I:C or C. parvum. In contrast, human peripheral blood leukocytes (PBL) depleted of monocytes by adherence on nylon wool demonstrated NK activity, which was not labile but rather increased substantially upon overnight culture at 37 degrees C alone or with poly I:C or C. parvum. Monocyte-depleted human PBL also produced IFN in these cultures. The pattern of reactivity seen with rat spleen cell cultures was different from either that of mouse and human cells. This pattern of reactivity had no lability at 37 degrees C and had a macrophage requirement for IFN production and NK cell augmentation upon culture alone or with poly I:C but not with C. parvum. These results indicated some major differences among species in the regulation of NK activity in vitro and the requirement for macrophages for the in vitro production of IFN. A better understanding of these differences will be helpful in choosing appropriate models for in vitro and in vivo studies of NK cell activity.