ABSTRACT
Autoimmune diseases and other inflammatory conditions are characterized by large lymphocytic tissue infiltrates in which T and B cells can be found in close contact. Here, using a murine airway inflammation model, we compare antigen-specific T and B cells in lung tissue versus lung-draining lymph node. In the lung we identify a B-cell population exhibiting a classical germinal centre phenotype without being organized into ectopic lymphoid tissue. By contrast, classical CXCR5(+) Bcl-6(+) T follicular helper cells are not present. Nevertheless, lung-infiltrating T cells exhibit follicular helper-like properties including the potential to provide help to naive B cells. The lung tissue is also a survival niche for memory T and B cells remaining in residual peribronchial infiltrates after resolution of inflammation. Collectively, this study shows the importance of T/B cooperation not only in lymph nodes but also in inflamed peripheral tissues for local antibody responses to infection and autoimmunity.
Subject(s)
B-Lymphocytes/immunology , Germinal Center/immunology , Lung/immunology , Lymphocyte Cooperation/immunology , Pneumonia/immunology , T-Lymphocyte Subsets/immunology , T-Lymphocytes, Helper-Inducer/immunology , Animals , Antibody Formation/immunology , Autoimmunity/immunology , Coculture Techniques , Disease Models, Animal , Enzyme-Linked Immunosorbent Assay , Flow Cytometry , Inflammation , Lymph Nodes/immunology , Lymphoid Tissue/immunology , Mice , Mice, Transgenic , Ovalbumin/toxicity , Pneumonia/chemically induced , Proto-Oncogene Proteins c-bcl-6 , Receptors, Antigen, T-Cell/genetics , Receptors, CXCR5ABSTRACT
The co-stimulators ICOS (inducible T cell co-stimulator) and CD28 are both important for T follicular helper (TFH) cells, yet their individual contributions are unclear. Here, we show that each molecule plays an exclusive role at different stages of TFH cell development. While CD28 regulated early expression of the master transcription factor Bcl-6, ICOS co-stimulation was essential to maintain the phenotype by regulating the novel TFH transcription factor Klf2 via Foxo1. Klf2 directly binds to Cxcr5, Ccr7, Psgl-1, and S1pr1, and low levels of Klf2 were essential to maintain this typical TFH homing receptor pattern. Blocking ICOS resulted in relocation of fully developed TFH cells back to the T cell zone and reversion of their phenotype to non-TFH effector cells, which ultimately resulted in breakdown of the germinal center response. Our study describes for the first time the exclusive role of ICOS and its downstream signaling in the maintenance of TFH cells by controlling their anatomical localization in the B cell follicle.