Human adherent mononuclear blood cells: cytolytic and cytostatic activity and characterization of effector cells during in vitro culture.

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-205), 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 alpha-naphthyl-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 of 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.