Longitudinal course of IL-1β-induced IL8-production for the fatigued and non-fatigued group. Whole blood samples obtained from participants assigned to the fatigued group (black circles, n = 55) and non-fatigued group (white squares, n = 353) were stimulated for 24 h with 30 ng/mL IL-1β. The amount of IL-8 in the culture supernatant was measured by ELISA, at the assessments before deployment (T0), and 1 month (T1) and 6 months (T2) after return from deployment. The longitudinal course of IL-1β-induced IL-8 production differed between the two groups (time: F(1.96; 794.68): 2.60, P = 0.076; group: F(1,406): 5.27, P < 0.05; time x group: F(1.96: 794.68): 4.30, P < 0.05). The IL-1β-induced IL-8 production of the non-fatigued group decreased over time (time: F(1.96, 690.66): 13.57, P < 0.001). In contrast, the amount of IL-1β-induced IL-8 production of the fatigued group did not significantly change over time (time: F(1.80, 97.19): 2.30, P = 0.111). IL-1β-induced IL-8 production significantly differed between the fatigued and non-fatigued group at T2 (P < 0.01), but not at T0 (P = 0.867) or T1 (P = 0.062). Data are presented as mean ± SEM. **P < 0.01.