Although there is cross-sectional evidence that changes in the immune system contribute to the pathophysiology of depression, longitudinal data capable of elucidating cause and effect relationships are lacking.
Epidemiology and Biostatistics Unit, Department of Clinical and Biomedical Sciences, Barwon Health, The University of Melbourne, PO Box 281, Geelong 3220, Australia. juliep@barwonhealth.org.au