Stimulation of allergen-loaded macrophages by TLR9-ligand potentiates IL-10-mediated suppression of allergic airway inflammation in mice

Background: Previously, we demonstrated that OVA-loaded macrophages (OVA-M) partially suppress OVA-induced airway manifestations of asthma in BALB/c mice. In vitro studies showed that OVA-M start to produce IL-10 upon interaction with allergen-specific T cells, which might mediate their immunosuppressive effects. Herein, we examined whether IL-10 is essential for the immunosuppressive effects of OVA-M in vivo, and whether ex vivo stimulation of the IL-10 production by OVA-M could enhance these effects.

Methods: Peritoneal M were loaded with OVA and stimulated with LPS or immunostimulatory sequence oligodeoxynucleotide (ISS-ODN) in vitro. The increase of IL-10 production was examined and, subsequently, ex vivo stimulated OVA-M were used to treat (i.v.) OVA-sensitized mice. To further explore whether Mphi-derived IL-10 mediates the immunosuppressive effects, Mphi isolated from IL-10(-/-) mice were used for treatment.

Results: We found that stimulation with LPS or ISS-ODN highly increased the IL-10 production by OVA-Mphi (2.5-fold and 4.5-fold increase, respectively). ISS-ODN stimulation of OVA-M significantly potentiated the suppressive effects on allergic airway inflammation. Compared to sham-treatment, ISS-ODN-stimulated OVA-Mphi suppressed the airway eosinophilia by 85% (vs. 30% by unstimulated OVA-Mphi), IL-5 levels in bronchoalveolar lavage fluid by 80% (vs. 50%) and serum OVA-specific IgE levels by 60% (vs. 30%). Importantly, IL-10(-/-)Mphi that were loaded with OVA and stimulated with ISS-ODN ex vivo, failed to suppress OVA-induced airway inflammation.

Conclusions: These results demonstrate that Mphi-derived IL-10 mediates anti-inflammatory responses in a mouse model of allergic asthma, which both can be potentiated by stimulation with ISS-ODN.