Effects of recombinant human interleukin-12 on eosinophils, airway hyper-responsiveness, and the late asthmatic response

Background interleukin-12 (IL-12) is a macrophage-derived cytokine that mod ulates T lymphocyte responses and has the capacity to suppress allergic and eosinophilic inflammation. Methods We carried out a double-blind, randomised, parallel group clinical study, in which patients with mild allergic asthma were given subcutaneous recombinant human IL-12 at increasing weekly injections of 0 .1, 0 . 25, 0 .5 mug/kg (n=19), or placebo (n=20). We compared responses to inhaled aller gen challenge 24 h before the first injection and 24 h after the final inje ction. Airways hyper-responsiveness and concentrations of peripheral blood eosinophils and sputum eosinophils were also assessed. Findings IL-12 caused a significant decrease from baseline in the main peri pheral brood eosinophil count 24 h after the fourth injection compared with placebo (p=0 . 0001). Sputum eosinophils were also significantly decreased 24 h after allergen challenge when treated with IL-12 compared with placeb o (p=0 . 024). IL-12 caused a non-significant trend towards improvement in airway hyper-responsiveness to histamine, but had no significant effect on the late asthmatic reaction after inhaled allergen challenge. After adminis tration of IL-12, four of 19 patients withdrew prematurely; two with cardia c arrhythmias, one with abnormal liver function, and a single patient with severe flu-like symptoms. Interpretation We have shown that IL-12 lowers numbers of blood and sputum eosinophils, but without any significant effects on airway hyper-responsive ness or the tate asthmatic reaction. This questions the role of eosinophils in mediating these reactions, and has important implications for developme nt of new anti-inflammatory treatments.