Colloidal gold uptake as a marker for monocyte differentiation and maturation in normal and leukemic cells

The uptake of colloidal gold particles by human monocytes was studied by electron microscopy, with special emphasis on changes in this uptake during the differentiation and maturation of these cells. The way in which leukemic cells of childhood acute non-lymphocytic leukemia (ANLL) can function in this gold uptake was also examined. In monocytes, microendocytosis was temperature-dependent; colloidal gold uptake increased as temperatures rose from 4 degrees C to 37 degrees C. It appeared that gold particles first adhered to the cell surface membrane, were then incorporated into the cytoplasmic vesicles, and then were transported into the granules. Original HL-60 cells and retinoic acid (RA)-treated HL-60 cells, which were differentiating and maturing along the granulocyte lineage, did not ingest colloidal gold particles, but 1,25(OH)2D3-treated HL-60 cells showed colloidal gold uptake during their differentiation and maturation along the monocyte lineage: 68.6% of the cells contained gold particles. Gold uptake was demonstrated in 27.3% of original U937 cells; the percentage increased to 70.3% when they were induced to mature by RA. In 15 specimens of childhood ANLL, none of the M1, M2 or M3 cells showed colloidal gold uptake, whereas 76-97% of M4 and M5 cells showed this uptake. These findings indicate that colloidal gold uptake is a marker of monocyte differentiation and maturation and can provide additional information for ANLL cytology.