Activation of mouse macrophages by pyran copolymer and role in augmentation of natural killer activity

Inoculation of mice with pyran copolymer resulted in activation of natural killer (NK) cells as well as macrophages. Conditions optimal for the boosting of NK activity seemed to differ from those optimal for macrophage activation as assessed by cytostasis of tumor target cells. Peak levels of macrophage cytostatic reactivity were found at about 7 days after drug injection and were only achieved by the highest doses of pyran tested. Macrophage activation was consistently higher in the peritoneal cavity than in the spleen, regardless of route of administration, in contrast to the failure of i.v. pyran to induce high NK reactivity in peritoneal exudate cells. At 2–3 days after pyran treatment of older mice, NK augmentation reached peak levels, but only minimal macrophage activation was found. Despite these differences, macrophages played a role in regulating NK activity in pyran‐treated mice. Functional macrophages appeared to be required for augmentation of NK activity by pyran, since boosting was impaired by prior in vivo inoculation of silica. Macrophages also appeared able to inhibit NK activity. In younger mice that exhibited high spontaneous levels of NK activity, pyran treatment produced a substantial reduction in NK activity to levels below those of untreated mice. This depression coincided with the time of peak levels of macrophage cytostasis. Furthermore, removal of adherent cells from the spleen cells of these pyran‐treated mice resulted in levels of NK activity almost as high as those of untreated mice. The possibility that the depression of NK activity in young mice by pyran copolymer is due to suppressor cells is discussed.