Tertiary lymphoid structures (TLS) resemble follicles of secondary lymphoid organs and develop in non-lymphoid tissues upon inflammation and cancer. However, the cell types and signals driving the development of TLS are unknown. The lack of suitable models to study TLS development precludes our understating of whether TLS play an active role in mediating immune responses. To investigate early events of TLS development in the lungs, we generated a robust model that relies on repeated instillation of p(I:C) plus ovalbumin (Ova) intranasally. This model produced TLS of different maturation entities, mimicking those observed in patient cohorts. We found that TLS development crucially depends on type I (IFN-I)- but not type III interferon (IFN-III)-signaling. IFN-I promoted lymphotoxin (LT) in lymphoid cells, which stimulated stromal cells to produce the B-cell-attracting chemokine CXCL13 via LTβR-signaling. Also, IFN-I sensing by stromal cells induced the production of T-cell-attracting chemokines CXCL9, CXCL10 as well as CCL19 and CCL21 independently of LTβR. Consequently, B-cell aggregates developed within a week, whereas mature TLS bearing follicular dendritic cells and germinal centers appeared after 3 weeks. We then studied the contribution of experimentally induced TLS to anti-tumor immunity and found that T-cells are recruited to TLS irrespective of their antigen specificity. Using preclinical tumor models, we found that TLS induction exacerbated tumor burden and metastatic outgrowth, suggesting that unspecific and persistent inflammation promotes tumor development. These findings elucidate key signaling pathways driving TLS development in the lungs. The development of suitable models and techniques is necessary to understand the role of TLS in a variety of pathologies including cancer
