Kuhlman KR, et al. - In a healthy sample of young adults, it was investigated if fluctuations in inflammation following a mild immune stimulus were associated with changes in daily reported features of depression for up to a week. In the absence of any physical symptoms, minor increases in inflammation were found to be related to corresponding increases in features of depression. In addition, even in high-risk and vulnerable populations, the influenza vaccine could be used to probe causal links with a high degree of ecological validity, to better understand the role of inflammation in the pathogenesis of depression.