IL-15-deficient mice develop enhanced allergic responses to airway allergen exposure.

Background: Interleukin-15 is a pleiotropic cytokine that is critical for the development and survival of multiple haematopoietic lineages. Mice lacking IL-15 have selective defects in populations of several pro-allergic immune cells including natural killer (NK) cells, NKT cells, and memory CD8 T cells. We therefore hypothesized that IL-15 mice will have reduced inflammatory responses during the development of allergic airway disease (AAD).

Objective: To determine whether IL-15 mice have attenuated allergic responses in a mouse model of AAD.

Methods: C57BL/6 wild-type (WT) and IL-15 mice were sensitized and challenged with ovalbumin (OVA), and the development of AAD was ascertained by examining changes in airway inflammatory responses, Th2 responses, and lung histopathology.

Results: Here, we report that IL-15 mice developed enhanced allergic responses in an OVA-induced model of AAD. In the absence of IL-15, OVA-challenged mice exhibited enhanced bronchial eosinophilic inflammation, elevated IL-13 production, and severe lung histopathology in comparison with WT mice. In addition, increased numbers of CD4 T and B cells in the spleens and bronchoalveolar lavage (BAL) were also observed. Examination of OVA-challenged IL-15Rα animals revealed a similar phenotype resulting in enhanced airway eosinophilia compared to WT mice. Adoptive transfer of splenic CD8 T cells from OVA-sensitized WT mice suppressed the enhancement of eosinophilia in IL-15 animals to levels observed in WT mice, but had no further effects.

Conclusion And Clinical Relevance: These data demonstrate that mice with an endogenous IL-15 deficiency are susceptible to the development of severe, enhanced Th2-mediated AAD, which can be regulated by CD8 T cells. Furthermore, the development of disease as well as allergen-specific Th2 responses occurs despite deficiencies in several IL-15-dependent cell types including NK, NKT, and γδ T cells, suggesting that these cells or their subsets are dispensable for the induction of AAD in IL-15-deficient mice.