HUMAN ADHERENT MONONUCLEAR BLOOD CELLS: CYTOLYTIC AND CYTOSTATIC ACTIVITY AND CHARACTERIZATION OF EFFECTOR CELLS DURING IN VITRO CULTURE

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Abstract
Using a methyl‐3H‐thymidine release assay, the cytolytic activity of human adherent mononuclear blood cells (AC) against three transformed human tumour cell lines of mesenchymal (U‐20S), epithelial (NHIK 3025) and hematogenous (K‐562) origin was compared to the activity against non‐transformed skin fibroblasts (U‐2S) and mesothelial cells (meso). Only transformed target cells were affected by the spontaneous cytolytic activity of normal AC tested after 0, 4 or 8 days of in vitro culture. Lymphokine‐activated 4‐days old AC also preferentially lysed transformed target cells, but low levels of lysis of non‐transformed target cells were observed at high effector cell densities. Freshly isolated AC were spontaneously cytostatic to K‐562, but not to NHIK 3025 cells, while differentiated AC cultured for 8 days were cytostatic to both cell lines. Lymphocyte‐like cells comprised up to 10% of freshly isolated AC, and most of these lymphocytes seemed to be non‐T‐cells as evaluated by α‐naphtyl‐esterase (ANAE) staining. Most of these cells detached during the first 24 h of in vitro culture. and the fraction of AC expressing monocyte markers (diffuse ANAE reactivity, interaction with ox erythrocytes coated with IgG or IgM + complement, interaction with Candida albicans) increased to nearly 100% after 4–8 days of in vitro culture. Thus, the effector cells expressing spontaneous cytolytic activity in this system have monocyte characteristics after 1 day of in vitro culture. However, contribution of adherent non‐monocytic cells to the cytotoxicity observed during the first 24 hours of culture can not be ruled out.