Objective: To explore the functional changes of T lymphocyte from PD-1⁻/⁻ mice and the effects on atherogenic immune responses.
Methods: PD-1⁻/⁻ mice were mated with ApoE⁻/⁻ mice to obtain PD-1⁻/⁻ApoE⁻/⁻mice. PD-1⁻/⁻ApoE⁻/⁻ mice were used as control. Both groups had a high-lipid diet for 12 weeks. Then the samples of aortic sinuses were harvested for oil-red and immunohistochemical stains. Samples of spleen and sera were obtained. Numbers of lymphocytes in spleen were evaluated by flow cytometry (FACS). And the cells of proliferation were also measured. The intracellular and serum cytokines were detected by enzyme-linked immunosorbent assay (ELISA).
Results: After a 12-week high-lipid diet, aortic root revealed more lesions in PD-1⁻/⁻ApoE⁻/⁻ mice than in PD-1⁺/⁺ ApoE⁻/⁻ controls ((0.51 ± 0.08) vs (0.29 ± 0.06) mm², t = 2.36, P < 0.01)). There was a significant increase in CD3 T cells in the lesions of PD-1⁻/⁻ApoE⁻/⁻ mice ((154.88 ± 36.64)/mm² vs (59.38 ± 25.28)/mm², t = 2.14, P < 0.01). In PD-1⁻/⁻ApoE⁻/⁻ mice, the numbers of total cells ((8.59 ± 0.55)× 10⁷) and cells in CD4⁺ and CD8⁺ T lymphocyte subsets ((1.53 ± 0.18)× 10⁷ and (1.41 ± 0.15)×10⁷), increased significantly than those in control mice ((6.29 ± 0.39)×10⁷, (0.94 ± 0.10)×10⁷ and (0.70 ± 0.09)× 10⁷ respectively, t = 3.43, 2.88, 4.03, all P < 0.05). Same changes were detected in both CD3⁺ CD62L(-) and CD3⁺ CD25⁺ cells. PD-1 deficiency in both CD4⁺ and CD8⁺ T cells resulted in enhanced proliferation by either macrophages or dendritic cells as antigen presenting cells (APCs). The supernatant levels of interleukin-2 (IL-2) ((53.38 ± 5.94) pg/ml), interferon-γ (IFN-γ) ((114.50 ± 9.69) pg/ml) and tumor necrosis factor-α (TNF-α) ((326.00 ± 22.25) pg/ml ) from PD-1⁻/⁻ T cells co-cultured with CD3 were significantly higher than those of control T cells ((15.63 ± 2.23), (33.25 ± 4.16) and (64.50 ± 8.17) pg/ml respectively, t = 5.95, 7.70, 11.03, all P < 0.01). However, only the serum levels of TNF-α increased in PD-1⁻/⁻ApoE⁻/⁻mice compared with control.
Conclusions: PD-1 deficiency in T cells increase markedly immune responses. And it is one of the mechanisms in atherogenesis.