CD27 co-stimulation increases the abundance of regulatory T cells and reduces atherosclerosis in hyperlipidaemic mice.

Aims: The co-stimulatory receptor CD27 modulates responses of T cells, B cells, and NK cells. Various T cell subsets participate in atherogenesis. However, the role of CD27 in atherosclerosis remains unexplored. Methods and results: Here we investigated the effect of bone marrow-derived and systemic CD27 deficiency in Apolipoprotein E-deficient (Apoe-/-) mice in early and advanced stages of atherosclerosis. Lethally-irradiated Apoe-/- mice reconstituted with Cd27-/-Apoe-/- bone marrow and consuming an atherogenic diet displayed a markedly increased plaque size and lesional inflammation compared to mice receiving Cd27+/+Apoe-/- bone marrow. Accordingly, chow diet-fed Cd27-/-Apoe-/- mice showed exacerbated lesion development and increased inflammation at the age of 18 weeks. At a more advanced stage of atherosclerosis (28 weeks), lesion size and phenotype did not differ between the two groups. Systemic and bone marrow-derived CD27 deficiency reduced the abundance of regulatory T cells (Treg) in blood, lymphoid organs, and the aorta. Numbers of other immune cells were not affected while expression of inflammatory cytokine genes (e.g. IL-1ß and IL-6) was increased in the aorta when haematopoietic CD27 was lacking. In vitro, Tregs of CD27-deficient mice showed similar suppressive capacity compared with their wild-type controls and migrated equally towards CCL19 and CCL21. However, thymic Cd27-/- Tregs underwent increased apoptosis and expressed fewer markers of proliferation in vivo. Reconstitution of Cd27-/-Apoe-/- mice with Cd27+/+Apoe-/- Tregs reversed the increase in atherosclerosis. Conclusion: We demonstrate that CD27 co-stimulation increases the number of Tregs and limits lesion development and inflammation in experimental atherosclerosis, particularly during early stages of disease. Thus, our study suggests that promotion of CD27 function may mitigate atherosclerosis.

CD70 limits atherosclerosis and promotes macrophage function.

The co-stimulatory molecule CD70 is expressed on activated immune cells and is known to modulate responses of T, B, and NK cells via its receptor CD27. Until now, there is only limited data describing the role of CD70 in atherosclerosis. We observed that ruptured human carotid atherosclerotic plaques displayed higher CD70 expression than stable carotid atherosclerotic plaques, and that CD70 expression in murine atheroma localized to macrophages. Lack of CD70 impaired the inflammatory capacity (e. g. reactive oxygen species and nitric oxide production) of bone marrow-derived macrophages, increased both M1-like and M2-like macrophage markers, and rendered macrophages metabolically inactive and prone to apoptosis. Moreover, CD70-deficient macrophages expressed diminished levels of scavenger receptors and ABC-transporters, impairing uptake of oxidised low-density lipoprotein (oxLDL) and cholesterol efflux, respectively. Hyperlipidaemic Apoe-/- mice reconstituted with CD70-deficient bone marrow displayed a profound increase in necrotic core size, plaque area, and number of lesional macrophages as compared to mice receiving control bone marrow. Accordingly, 18 week-old, chow diet-fed CD70-deficient Apoe-/- mice displayed larger atheroma characterised by lower cellularity and more advanced plaque phenotype than Apoe-/- mice. In conclusion, CD70 promotes macrophage function and viability and is crucial for effective phagocytosis and efflux of oxLDL. Deficiency in CD70 results in more advanced atheroma. Our data suggest that CD70 mitigates atherosclerosis at least in part by modulating macrophage function.