To test for an empirically derived threshold of IL-8 at which endotoxin no longer elicited significantly greater increases in depressed mood relative to placebo, sensitivity analyses were conducted to examine the simple effect of condition (endotoxin vs. placebo) on POMS depression change from baseline to T2, across the full range of baseline levels of IL-8. This evidence concerns the gene CXCL8 and major depressive disorder.