The effect of adherence on the in vitro induction of cytocidal activity by macrophages.

The effects of macrophage adherence to plastic on tumoricidal activity were investigated. In order to do so, an agarose culture system was developed to provide a means for maintaining non-adherent macrophages in vitro. We were not able to show any effects of adherence on tumour cell lysis by activated macrophages. On the other hand, in vitro activation of non-adherent macrophages was possible only if adherence was replaced by another triggering signal. This requirement was more significant in the A/J mouse strain, where non-adherent macrophages required longer activation periods. Hence we propose that adherence might provide a second signal for the in vitro induction of tumour killing. The biological significance of adherence that is relevant to tumour killing is discussed.