CD28 and hip fracture: Similarly, the frequency of CD28-ve CD57+ve CD8 T cells were also significantly different, F (2, 56) = 4.12, p = .02, η2 = .12 between the three groups [Additional file 1: Figure S1b], due to a significant increase in frequency of CD28-ve CD57+ve CD8 T cells in hip fracture patients with depressive symptoms compared with healthy controls, p = .02 but not in comparison with hip fracture patients without depressive symptoms, p = .49.