Inefficient Lymph Node Sensitization during Respiratory Viral Infection Promotes IL-17–Mediated Lung Pathology

Abstract

Development of bronchus-associated lymphoid tissue has been suggested to enhance local antiviral immune responses; however, ectopic lymph node formation often corresponds to chronic inflammatory diseases. These studies investigated the role of ectopic pulmonary lymph nodes upon respiratory syncytial virus (RSV) infection using CCR7-deficient mice, which develop bronchus-associated lymphoid tissue early in life. CCR7−/− mice exhibited impaired secondary lymph node formation, enhanced effector T cell responses and pathogenic mucus production in the lung after RSV infection. IL-17 production from CD4 T cells in CCR7−/− mice was most remarkably enhanced. Wild-type animals reconstituted with CCR7−/− bone marrow recapitulated the pathogenic lung phenotype in CCR7−/− mice, whereas CCR7−/− animals reconstituted with wild-type bone marrow had normal lymph node development, diminished IL-17 production and reduced lung pathology. Mixed bone marrow chimeras revealed an alteration of immune responses only in CCR7−/− T cells, suggesting that impaired trafficking promotes local effector cell generation. Lymphotoxin-α–deficient mice infected with RSV were used to further examine locally induced immune responses and demonstrated increased mucus production and amplified cytokine responses in the lung, especially IL-17. Neutralization of IL-17 in CCR7−/− or in lymphotoxin-α–deficient animals specifically inhibited mucus hypersecretion and reduced IL-13. Thus, immune cell trafficking to secondary lymph nodes is necessary for appropriate cytokine responses to RSV as well as modulation of the local environment.