Background: T helper (Th)1 cytokines have a critical role in facilitating the elimination of intracellular pathogens. Interleukin (IL)-15 is a Th1 cytokine, having biological activities similar to IL-2.

Patients and Methods: In the present study, we evaluated IL-15 serum levels in patients with different clinical forms of brucellosis and healthy controls. We also aimed at assessing the potential role of serum IL-15 as a prognostic marker for human brucellosis.

Results: Patients with acute brucellosis (n=50) had significantly higher levels of IL-15 in comparison with both patients with chronic brucellosis (n=32) (44.1±12.1 vs 5.2±3 ρg/ml, p<0.01) and healthy controls (n=65) (8.7±4.3 ρg/ml, p<0.01). IL-15 levels were significantly higher among patients with fever >38° C (n=65), in comparison with subjects who had no fever (n=17) (43.3±12.3 vs. 5.9±3.2 ρg/ml, p<0.01). On the contrary, IL-15 serum concentration was similar in patients with uncomplicated brucellosis (41.1±16.6 ρg/ml) and patients with visceral complications (44.9±11.1 ρg/ml). Following a complete antibiotic course, IL-15 levels showed a slight, not significant decrease among patients with acute brucellosis (from 44.1±12.1 ρg/ml to 37.3±16.1), whereas patients with chronic brucellosis had a significant increase in IL-15 serum concentration (from a pre-treatment value of 5.2±3 pg/ml to a post-treatment level of 24±10.6 ρg/ml, p<0.05).

Conclusions: IL-15 production seems to be defective in chronic brucellosis. Further studies should clarify the mechanisms regulating IL-15 release during the course of brucellosis.