title: Normal human monocytes inhibit tumor cell growth in vitro.
abstract: Normal human monocytes were evaluated in an in vitro assay of growth inhibition of tumor cells. Monocytes were isolated from the blood of 6 normal subjects by Ficoll-Hypaque separation and adherence to plastic microtest wells. Cervical carcinoma cells (HeLa) were added to the microwells to result in a ratio of 50 monocytes to one HeLa cell. Cultures were then incubated for 6 to 46 hr. Growth inhibition was evaluated by measuring the uptake of 3H-thymidine over a 4-hr pulse period after 2, 18, or 42 hr of monocyte-HeLa interaction. Inhibition of HeLa growth by monocytes was 23.8% +/- 8.6% over 6 hr, 22.0% +/- 8.9% over 22 hr. and 68.3% +/- 7.5% over 46 hr. Growth inhibition of HeLa cells was confirmed by direct enumeration of HeLa cells at the end of coincubation. Attachment of monocytes to the HeLa cells was confirmed by light and scanning electron micrographs. Granulocytes, lymphocytes, and other cell lines did not comparably inhibit HeLa growth and media replenishment did not ablate the effect. These data demonstrate that normal human monocytes can inhibit the growth of a malignant cell line in vitro in the absence of overt activation procedures.
mesh_terms: D002455:Cell Division; D002460:Cell Line; D006367:HeLa Cells; D006801:Humans; D009000:Monocytes