Suppression of the reactive oxygen intermediates production of human macrophages by colorectal adenocarcinoma cell lines

Although some in vitro studies indicate that macrophages exert cytotoxic re sponses against tumour cells by production of reactive oxygen intermediates (ROI), no obvious impairment of tumour cell growth is visible in various h uman malignant tumours, which contain a large number of tumour-associated m acrophages (TAM). We made use of an in vivo-like co-culture model of multic ellular tumour spheroids of three colon carcinoma cell lines (HRT-18, HT-29 , CX-2) and three functionally different phenotypes of human macrophages (2 7E10, RM3/1, 25F9) to investigate if tumour cells deactivate macrophage cyt otoxicity. The production of ROI was measured by a lucigenin-amplified chem iluminescence assay in a 96-well-microplate luminometer. Different capabili ties to produce ROI by different macrophage phenotypes were observed. Howev er, independent of the macrophage phenotype and the tumour cell type a sign ificant inhibition of ROI formation was found in cocultures after 1 hr, 1 a nd 2 days. Macrophages were also suppressed by tumour cell supernatants, wh ich contained anti-inflammatory cytokines transforming growth factor-pi (TG F-beta 1) and negligible levels of interleukin-4 (IL-4) and IL-10 as shown by enzyme-linked immunosorbent assay (ELISA). Although recombinant human cy tokines TGF-beta 1, IL-10 and IL-4 inhibited the production of ROI in fresh ly isolated monocytes, these cytokines had no effect on differentiated macr ophage phenotypes, indicating that these cytokines are not involved in medi ating tumour-induced suppression of ROI production by human macrophages.