Chemokine CCL19 promotes type 2 T-cell differentiation and allergic airway inflammation

Allergic asthma is driven largely by allergen-specific T_H2 cells, which develop in regional lymph nodes on the interaction of naive CD4⁺ T cells with allergen-bearing dendritic cells that migrate from the lung. This migration event is dependent on CCR7 and its chemokine ligand, CCL21. However, is has been unclear whether the other CCR7 ligand, CCL19, has a role in allergic airway disease.

This study sought to define the role of CCL19 in T_H2 differentiation and allergic airway disease.

Ccl19-deficient mice were studied in an animal model of allergic asthma. Dendritic cells or fibroblastic reticular cells from wild-type and Ccl19-deficient mice were cultured with naive CD4⁺ T cells, and cytokine production was measured by ELISA. Recombinant CCL19 was added to CD4⁺ T-cell cultures, and gene expression was assessed by RNA-sequencing and quantitative PCR. Transcription factor activation was assessed by flow cytometry.

Lungs of Ccl19-deficient mice had less allergic airway inflammation, reduced airway hyperresponsiveness, and less IL-4 and IL-13 production compared with lungs of Ccl19-sufficient animals. Naive CD4⁺ T cells cocultured with Ccl19-deficient dendritic cells or fibroblastic reticular cells produced lower amounts of type 2 cytokines than did T cells cocultured with their wild-type counterparts. Recombinant CCL19 increased phosphorylation of STAT5 and induced expression of genes associated with T_H2 cell and IL-2 signaling pathways.

These results reveal a novel, T_H2 cell-inducing function of CCL19 in allergic airway disease and suggest that strategies to block this pathway might help to reduce the incidence or severity of allergic asthma.