The Complex Role of Target Cells in the Effects of Soluble Substances Released by Monocyte—Macrophage Cell Populations

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Abstract
Supernatants of human peripheral blood monocytes (SMØ) and the nondialysable fraction (NDF) and dialysable fraction (DF) thereof were tested for their effects on human peripheral blood mononuclear cells not depleted of adherent cells (TC) or progressively depleted of adherent cells (NAC) and on human thymocytes alone or supplemented with human monocytes (MØ) obtained from peripheral blood. PHA, Con A and PPD were used as stimulants of the target cells. A standard SMØ (from MØ cultured at 2 × 105 cells/ml), which did not produce any detectable effect on TC, enhanced the responses of NAC that had been partially depleted of adherent cells and of thymocytes not supplemented with MØ, and suppressed the response of NAC more completely depleted of adherent cells. The NDF increased the level of 3H‐thymidine uptake by thymocytes or peripheral blood mononuclear cells when the cell populations were depleted of adherent cells and stimulated by PHA, Con A, or PPD; NDF suppressed 3H‐thymidine uptake by populations of peripheral blood mononuclear cells not depleted of adherent cells and by populations of thymocytes supplemented with monocytes, under the same conditions of stimulation. The DF showed effects completely opposite to those of the NDF; i. e. cultures that were enhanced by NDF were suppressed by DF, and those enhanced by DF were suppressed by NDF. The suppressor effects of SMØ and of its subfractions were more evident in PPD‐stimulated cultures than in cultures stimulated by Con A or PHA, whereas the enhancing effect was most evident in Con A‐stimulated cultures. In both cases the PHA‐stimulated cultures were the least affected. Both the enhancing and suppressor effects were highly dependent on the dose of stimulant used.

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