Depressive symptoms in hip fracture patients are associated with reduced monocyte superoxide production

Ageing is accompanied by reduced functioning of the immune system, termed immunesenescence which is associated with increased risk of infection and mortality. However the immune system does not operate in isolation and can be modified by many environmental factors, including stress. In this study we determined whether physical stress (hip fracture) and psychological distress (depressive symptoms) had additive effects upon the aged immune system, specifically on monocyte numbers and function. We assessed immune function in 101 hip fracture patients (81 female) 6 weeks and 6 months after injury and 43 healthy age matched controls (28 females). Thirty-eight of the hip fracture group were found to be depressed at the 6 week sampling. No differences in peripheral monocyte count, distribution of monocyte subsets or TNFα secretion were observed between hip fracture patients and healthy controls. However we observed significantly reduced superoxide production in response to Escherichia coli in the monocytes of hip fracture patients who developed depressive symptoms compared with non-depressed hip fracture patients (p = 0.002) or healthy controls (p = 0.008) 6 weeks after the fracture which remained decreased 6 months following injury. In previous studies we have shown an effect of depression on neutrophil superoxide generation in hip fracture patients, suggesting a particular susceptibility of this aspect of immune cell function to psychological stress.