Lipopolysaccharide injection activates the immune system of honey bees. Relative expression levels of Defensin 2 (Def2), an immune response gene, are increased in the fat bodies of 7-day-old honey bee workers after saline- and lipopolysaccharide (LPS)-injection compared with untreated controls (sham). LPS-injection causes a significantly higher expression of Def2 than saline-injection. Relative expression levels of Def2 were monitored using quantitative real-time polymerase chain reaction using fat bodies from individual bees. Data were collected from two independent trials, and each trial used bees from a different source colony (sham: N = 18; saline: N = 16; LPS: N = 18). Figure shows the effects of treatments on mean ± standard error of the mean quantitative expression of Def2 RNA (F(2,46) = 31.702; P < 0.001). Post-hoc tests:* P < 0.05; *** P < 0.001.