TNF May Negatively Regulate Phagocytosis of Devil Facial Tumour Disease Cells by Activated Macrophages

ABSTRACT

Introduction: Macrophage phagocytosis of pathogens and tumour cells is an important early event in protection against infectious disease and cancer. As tumour necrosis factor α (TNF) is an important cytokine in macrophage activation, we investigated the involvement of TNF in macrophage phagocytosis of tumour cells.

Methods: We used Devil Facial Tumour Disease (DFTD) cancer cells as the target tumour cells. The Tasmanian devil (Sarcophilus harrisii) population is threatened by the transmissible DFTD. Using DFTD cells provided the opportunity to determine if these cells can be phagocytosed and investigate requirement for TNF. As effector cells, bone marrow derived macrophages (BMDMs), generated from C57BL/6 wild type (B6.WT) and C57BL/6 TNF-/- (B6.TNF-/-) mice were used. Phagocytosis of DFTD cells was investigated by confocal microscopy and flow cytometry.

Results: DFTD cells were consistently phagocytosed by B6.WT and B6.TNF-/- BMDMs with similar efficiency in vitro. Consequently the DFTD cells are not resistant to phagocytosis. Following activation by exposure to IFNγ and LPS or LPS alone, B6.TNF-/- BMDMs had higher phagocytic efficiency and lower nitric oxide (NO) production compared to wild-type controls. In addition, NO seems to be unlikely to be the involved in phagocytosis efficiency in IFNγ and LPS activated B6.TNF-/- macrophages and consequences thereof.

Conclusion: Our results indicate that TNF is not required for IFNγ and LPS or LPS alone activation of macrophage phagocytosis. TNF may negatively regulate macrophage phagocytosis of tumour cells.

KEYWORDS:

• Macrophages
• Devil Facial Tumour disease
• nitric oxide
• phagocytosis
• TNF

Acknowledgments

We thank Terry Pinfold for assistance using flow cytometry, and Peta Lawrie and Paul Scanon for animal husbandry. We also thank Yilan Zhen for advice on the performance of confocal microscopy. XL was supported by a AMU/UTAS postgraduate scholarship and research funds were provided by grants from the Australian Research Council (DP130100715, LP130100218) and the Dr Eric Guiler Tasmanian devil research grants administered through the University of Tasmania Foundation. Part of the data in this manuscript have been presented as poster at the ICI Melbourne in 2016 and have been published in the conference proceedings: Li X., Lyons A. B., Körner H. & G. Woods. (2016) Murine macrophage phagocytosis of Devil Facial Tumour Disease cells. European Journal of Immunology 46, 439 (supplement) Meeting Abstract 422. (published abstract).

Conflict of interest

The authors state that they had no conflict of interest.