Inhibitory effect of monocytes on "lymphokine activated killer" (LAK) cell activity

The effects of placing activated monocytes in the presence of LAK cells was investigated. It was shown that the addition of monocytes to a preparation of rIL2-stimulated lymphocytes decreased LAK cell activity. This inhibition is enhanced in the presence of rIFN gamma. To analyze the mechanisms of inhibition, monocytes and lymphocytes were cultured separately, on opposite sides of a porous membrane which allowed the passage of molecules. Under such conditions, monocytes inhibited the activity of LAK cells to the same degree that a mixed culture does, suggesting a possible role of diffusible factor(s). Neither indomethacin nor PGE2 fully inhibited LAK cell activity, indicating that PGE2 is not the major monocyte-derived factor inhibiting LAK cell activity. It was also demonstrated that LAK cells can kill monocytes, but that IFN gamma can protect the monocyte from the toxic effect. This protective mechanism may be responsible for enhancing the inhibitory activity of monocytes.