CD4 and major depressive disorder: Firstly, on examining the effect of hip fracture and depressive symptoms on Tregs, no significant differences were observed in the frequency of circulating CD4+CD25+Foxp3+ Tregs, which contradicts the findings of two previous studies showing a decline in Tregs in mice with depression-like behaviour (Kim et al. 2012) and in humans with major depression (Li et al. 2010).