In vitro function of radiocolloid-labelled monocytes

Human monocytes in a mononuclear cell suspension were labelled specifically using 111In-Fe-colloid, with the ultimate goal of using them for monocyte kinetic studies in haematological malignancies. In order to examine the function of the labelled monocytes, in vitro function tests were performed on cell suspensions containing labelled or non-labelled monocytes. These tests were: phagocytosis of opsonized zymosan particles and ability of monocytes to mature into macrophages when cultured in glass tissue chambers. There were no significant differences in in vitro function between labelled and non-labelled monocytes. Cell viability was always greater than 90%. During culture, a rapid loss of monocyte-bound radioactivity took place. We conclude that the labelling procedures do not interfere with subsequent in vitro cell function. However, because of the rapid loss of cell bound radioactivity in vitro, monocytes labelled by this method do not seem suited for long-term studies in vivo.