2A, panel III compared with Fig. 1A panel VI). Based on the results in our 3D collagen culture experiments, we cannot conclude that enhanced neutrophil accumulation into tumour colonies also led to enhanced tumour destruction.

However, previous in vitro studies demonstrated that increased effector to target ratios resulted in increased tumour cell killing by neutrophils [8, 10]. It was demonstrated that TNF-α acts not only as a chemo-attractant for neutrophils, but also induces IL-8 production by endothelial cells, which is the prototypic neutrophil chemokine [5]. We therefore tested IL-8 concentrations in supernatants of the collagen cultures. In the presence of FcαRIxHer-2/neu BsAb, low amounts of IL-8 were detected in the absence of HUVECs (Fig. 2C). However, the IL-8 concentration was profoundly amplified in the presence of HUVECs and an FcαRIxHER-2/neu BsAb, supporting the Selleck PARP inhibitor idea that HUVECs produced IL-8 after activation by neutrophils. No IL-8 was detected in the supernatant of collagen cultures in which an anti-Her-2/neu IgG mAb had been added (data not shown). To confirm IL-8 production by HUVECs in resp-onse

to factors that had been secreted by activated neutrophils, we cultured check details HUVEC monolayers in the presence of supernatant that had been harvested from collagen cultures in which SK-BR-3 colonies had been incubated with neutrophils and an FcαRIxHer-2/neu BsAb (in the absence of HUVECs). Although minimal IL-8 levels were detected in the harvested supernatant, the IL-8 concentration increased when this supernatant was added to HUVEC monolayers, indicating IL-8 production by HUVECs (Fig. 2D). Interestingly, the peak of neutrophil migration was observed after 4 h, at which time hardly any IL-8 release was found (Fig. 2B and C). IL-8 therefore does not appear to play a major Ribonucleotide reductase role in our in vitro experiments, but migration is likely due to release of LTB4 after targeting FcαRI (Fig. 1D and [21]). LTB4 not only acts as chemoattractant, but also

affects the vascular permeability of endothelial cells and transendothelial neutrophil migration [30, 31]. Furthermore, IL-1β and TNF-α (which are also released after FcαRI triggering) are also known to up-regulate BLT receptors on HUVECs with concomitantly enhanced LTB4-mediated responses, such as vascular permeability and transendothelial neutrophil migration [32]. Taken together, targeting FcαRI on neutrophils resulted in release of LTB4, which acted as the major chemoattractant for neutrophil migration. Additionally, release of lactoferrin was observed, reflecting neutrophil degranulation, which resulted in tumour cell killing. IL-8 production was furthermore significantly increased in the presence of endothelial cells, which was due to endothelial cell activation by inflammatory mediators that had been released by neutrophils after activation.