The immune influence of a parabiosis model on tumour-bearing mice.

Aim: The aim of this study was to analyse the immune influence of a parabiosis model on tumour-bearing mice.

Methods: Parabiosis was established between C57BL/6 wild-type mice expressing green fluorescent protein (GFP+) and C57BL/6 wild-type mice without green fluorescent protein (GFP) to ensure blood cross-circulation between animals, and then the expression of CD4+ T cells, CD8+ T cells and interleukins 2, 4 and 10, and interferon-gamma (INF-γ) in spleen cells of parabiosis model mice were examined with flow cytometry. At day 8 and day 14 after conjoined surgery, we were aiming to sample tumour tissue in the parabiosis mice and observe changes of CD3, CD4, CD8, CD31, IFN-γ and vascular endothelial growth factor (VEGF) through immunohistochemical analysis.

Results: The interaction of blood was established on the third day with modelling rate of 85.7% after blood interaction. The healthy cells of GFP+ C57 mice entered the blood circulation of tumour-bearing mice via a connecting capillary network, playing a role in stimulating CD4+ and CD8+ cells in the tumour-bearing mice so that CD4+ cells increased more in tumour-bearing mice than in the positive control group (p <0.05). The number of GFP+ cells that were detected in a tumour-bearing mouse was small, but GFP+ cells can stimulate the mouse itself to generate more CD4+/interleukin (IL)-4, CD4+/IL-10 (p <0.05).The numbers of CD4+/IL-2, CD4+/IL-4 and CD4+/IL-10 among the GFP+ mice were higher than those in the negative control group(p <0.05).The levels of IFN-γ in both mice in the parabiosis model were decreased (p <0.05). The rate of CD4+/CD8+ in parabiosis GFP+ mice was higher than in the negative control group (p <0.05). In immunohistochemical tests, the rates of CD3, CD4, CD8 and IFN-γ positive cells was higher than in the positive control group, with their optical densities of 0.32 ± 0.63, 0.33 ± 0.00, 0.31 ± 0.91 and 0.28 ± 0.14 respectively (p <0.05). The expression of CD31 (0.19 ± 0.50) and VEGF (0.19 ± 0.21) were lower when compared with the positive control group, with no significant difference. CD31 and VEFG cell expression was low, at 0.19 ± 0.50 and 0.19 ± 0.21, respectively, compared with the positive control group (p >0.05). Values for CD31 and VEGF cells in the positive control group were higher, at 0.32 ± 0.35 and 0.29 ± 0.35, respectively, but when compared with the parabiosis tumour-bearing group, there was no significant difference. The expression of CD3, CD4, CD8 and IFN-γ cells at day 8 was low: 0.22, 0.17, 0.15 and 0.16, respectively. When compared with the parabiosis tumour-bearing group, there was no significant difference.

Conclusions: The established allogeneic parabiosis mice model can be well adapted to the conjoined state of mice and be applied in wide medical experiments. The parabiosis model has played an important role in studying immune regulation, which provides a basis for the future tumour immunotherapy. Parabiosis models can stimulate tumour-bearing mice to generate CD3, CD4, CD8 and IFN-γ, and play a notable role in immune regulation and tumour destruction. The positive expression rates of CD31 and VEFG cells in the parabiosis tumour-bearing group were lower; however, when compared with the positive control group, there was no significant difference.