Development of depressive symptoms post hip fracture is associated with altered immunosuppressive phenotype in regulatory T and B lymphocytes.

Hip fracture is a common physical trauma in older adults that is also associated with a high incidence of new onset depression. The immune system declines with age and is also compromised by physical and psychological stress. This study examined whether hip fracture and depressive symptoms had additive effects upon the aged immune system that might contribute to poor health outcomes after hip fracture. We assessed the frequency of regulatory T cells, Tregs (CD4(+) CD25(+) Foxp3(+)) and IL10 production by CD4 T cells, and the frequency and IL10 production by regulatory B cells, Bregs (CD19(+) CD24(hi) CD38(hi)) in 101 hip fracture patients (81 female) 6 weeks after injury and 43 healthy age-matched controls (28 female). 38 hip fracture patients (37%) developed depressive symptoms. Hip fracture did not have an effect on circulating Tregs frequency but a significant reduction in the frequency of Bregs was observed in patients who developed depression compared with non-depressed patients (p = 0.001) or healthy controls (p < 0.001). Bregs also showed a significant decline in IL10 production in depressed hip fracture patients compared with controls (p = 0.04) and non-depressed patients (p = 0.01). In contrast, there was an increase in IL10 production by CD4 T cells in hip fracture patients with new onset depression compared to hip fracture patients without depression (p = .04) and healthy controls (p = .02). We conclude that the reduced immunity associated with new onset depression post hip fracture could include a contribution by heightened Tregs function.