SOLUBLE FACTORS PRODUCED BY MACROPHAGES MONOCYTES INHIBIT LYMPHOKINE-ACTIVATED KILLER ACTIVITY IN RAT SPLENOCYTE CULTURES

In the present study we investigated the inhibition of interleukin-2(I L-2)-induced lymphokine-activated killer (LAK) activity in rat splenoc yte cultures in relation to the presence of 2-mercaptoethanol and macr ophages/monocytes. The presence of 2-mercaptoethanol is necessary for induction of LAK activity in rat splenocyte cultures. Removal of macro phages/monocytes from rat splenocytes by plastic or nylon-wool adheren ce, or iron ingestion resulted in LAK induction by IL-2 in the absence of 2-mercaptoethanol. The effect of macrophages/monocytes on LAK acti vity was also studied in transwell co-cultures. In the absence of 2-me rcaptoethanol, the induction of LAK activity was very low in macrophag e/monocyte-depleted splenocytes with macrophages/monocytes in the uppe r compartment of a transwell culture. In contrast, in the presence of 2-mercaptoethanol a high level of LAK activity was induced in these tr answell cultures, showing that 2-mercaptoethanol abolished the LAK-inh ibiting capacity of macrophages/monocytes. In addition, established LA K activity was strongly inhibited when, after LAK induction, splenocyt es were cultured with supernatant of unfractionated splenocytes, which were cultured with IL-2 but in the absence of 2-mercaptoethanol. Addi tion of 2-mercaptoethanol abrogated the inhibiting effect of the super natant completely. These experiments demonstrate that rat macrophages/ monocytes produce 2-mercaptoethanol-sensitive soluble LAK-inhibiting f actors. Ultrafiltration of conditioned culture medium of macrophages/m onocytes revealed the presence of LAK-inhibiting factors larger than 1 0 kDa. We concluded that 2-mercaptoethanol-sensitive soluble factors p roduced by macrophages/monocytes determine the level of LAK induction in rat splenocyte cultures.