Background Allergic asthma is a T-helper type 2 (Th2) cell-mediated chronic disease that is characterized by airway hyperreactivity (AHR) and chronic eosinophilic airway inflammation. Several studies suggest co-stimulatory molecules like CD137 as potential targets for therapeutic interventions in allergic airway disease. Recently, we could show in a murine asthma model that administration of an agonistic antibody against the receptor of the co-stimulatory molecule CD137 prevented and even reversed an already-established asthma phenotype.
Objective The purpose of this study was to analyse the effect of stimulation of the CD137 ligand by a monoclonal antibody (CD137L mAb).
Methods To induce an asthma-like phenotype, BALB/c mice were sensitized to ovalbumin (OVA), followed by an intrapulmonary allergen challenge. Anti-CD137L or control mAb were applied 1 day before OVA immunization or after the asthma phenotype was already established.
Results Stimulation of the CD137L instead of the receptor by CD137L mAb prevents the development of an asthma-like phenotype but does not reverse established disease. While the receptor-mediated effect is partly mediated by anergy of CD4+ T cells and partly by induction of IFN-γ-producing CD8+ T cells, the effect of the CD137L mAb is completely dependent on IFN-γ-producing CD8+ T cells: blockade of IFN-γ and depletion of CD8+ T cells fully abrogated the observed protective effect. In vitro experiments showed that the anti-CD137L mAb ligates directly to CD8+ T cells and induces the generation of IFN-γ by this cell population.
Conclusion Our results demonstrate that anti-CD137L mAb prevents disease development via IFN-γ-producing CD8+ T cells but is inferior to stimulation of the receptor that reverses established disease by a mechanism including CD4+ T cell anergy.