ICOS is critical for T follicular regulatory cell differentiation

The Inducible Costimulator (ICOS) is a T cell costimulatory receptor critical for humoral immunity. ICOS-deficient patients suffer from recurrent infections due to lack of protective antibodies. However, some patients also display signs of antibody-mediated autoimmunity. These findings may reflect a dual role of ICOS: facilitating the differentiation and function of T follicular helper (Tfh) and T follicular regulatory (Tfr) cells. While Tfh cells are known to provide help to B cells to produce high affinity antibodies, the main role of Tfr cells seems to be preventing autoantibody generation. Using Foxp3-cre-mediated ICOS knockout (ICOS FC) mice, we show that T regulatory (Treg)-specific ICOS deletion drastically reduces the number of Tfr cells without altering Treg cell numbers. Single cell RNA sequencing further revealed shifts in transitory Tfr precursor populations in immunized ICOS FC mice. Importantly, we observed a lowered ratio of antigen-specific germinal center B (GCB) cells and increased anti-nuclear antibodies in ICOS FC mice, suggesting a rise in autoreactive GCB cells. We also noted variations in isotype composition of total and virus-specific antibodies in infected ICOS FC mice. Mechanistically, our data suggests that ICOS could promote the Treg-to-Tfr transition by regulating CXCR5 expression. Thus, our study demonstrates that ICOS is critical for Tfr cell generation and supports the role of Tfr cells in preventing generation of autoantibodies during germinal center reactions.

Isolation and ex vivo expansion of murine bone marrow-derived group 2 innate lymphoid cells (MUC8P.734)

Group 2 innate lymphoid cells (ILC2) are recently discovered lymphocyte subpopulations that have innate ability to produce large quantities of a specific set of cytokines regulating innate and adaptive immune responses. Importantly, deregulated ILC2 responses are implicated in detrimental type 2 immunopathologies such as allergies, asthma and atopic dermatitis, as well as fibrotic disease, both in rodents and humans. However, the progress in our understanding of ILC2 biology has been hampered by their scarcity at steady state as well as infected and inflamed tissues. Here, a simple, efficient and reliable method is presented to isolate murine ILC2 from the bone marrow by flow cytometric cell sorting and further cultivate them using a defined cytokine cocktail, yielding a 500-fold expansion. The resulting ILC2 constitute a pure cell population and show the same phenotypic and functional characteristics as ILC2 in vivo. Thus, this protocol enables a high yield of ILC2 from murine bone marrow and thereby provides sufficient ILC2 numbers for standard cell and molecular biology assays. An in-depth understanding of the cellular and molecular mechanisms of ILC2 is essential for the development of new strategies and drugs to fight unwanted type 2 immunopathologies and fibrotic disease.

The development og CD138high Breg in AAD is dependent on Semaphorin 4C (IRM10P.614)

We have previously found that mice with Semaphorin 4C (Sema4C) deficient B cells exhibited exaggerated airway damage and pulmonary inflammation during allergic airways disease (AAD). We aimed to determine the mechanisms by which Sema4C on B-cells regulates AAD. Following allergen exposure, Sema4C-/- AAD mice had significantly fewer CD138high IL-10+ B cells (CD138high Breg) and significantly increased CD138high IL4+ B cells in spleen. In vitro, Sema4C-/- B cells consistently failed to differentiate into CD138high Breg under Th2 culture conditions. Adoptive transfer of Sema4C-/- plasma cells induced exacerbated Th2 responses, with airway eosinophilia and increased IL-4+ inflammatory cell infiltrates in the lungs. In contrast, transfer of CD138high Breg to WT mice with AAD dramatically alleviated airway inflammation. Co-culturing Sema4C-/- B cells with Sema4C transfected cells (Hek293-Sema4C) corrected impaired CD138high Breg development. Co-culture of B cells with Hek293-Sema4C decreased IgE production for both WT and Sema4C-/- B cells. Sema4C is essential for the development of CD138high Breg and may play a crucial role in the auto-regulation of B cells in allergic inflammation.