Relation of Depression, Natural Killer Cell Function, and Infections after Coronary Artery Bypass in Women

Background: After hospital discharge for coronary artery bypass grafting (CABG), infection is a common cause of morbidity. Although depression has been associated with immune dysfunction, its role in post-CABG infection is unknown. Aims: The purpose of this study was to: 1) compare natural killer cell cytotoxicity (NKCC) and post-hospitalization infections in depressed and non-depressed women after CABG; and 2) test whether NKCC mediated the relationship between post-discharge depression and infections. Methods: Sixty-seven women recovering from CABG were assessed for depression prior to hospital discharge and followed for six months. Major depression was identified by a structured clinical interview. Infections were identified by patient report using the Modified Health Review and by medical chart audit. Results: Compared to non-depressed women after CABG, women with major depression had reduced NKCC, more all-cause infections, and more self-reported illnesses. Although NKCC did not mediate the relationship between depression and wound (i.e. incisional) infections after CABG, it did mediate the relationship between depression and non-wound infections, including pneumonias and upper respiratory infections. Conclusions: For the first six months after CABG, women with major depression are at increased risk for infections. Natural killer cell cytotoxicity may be related to this phenomenon, particularly to non-wound infections.