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Molecular characterization of survival niches for memory T helper cells in bone marrow

Applicant Dr. Koji Tokoyoda
Subject Area Immunology
Term from 2016 to 2019
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 310702922
 
Final Report Year 2020

Final Report Abstract

A depletion of activated/effector cells can suppress pathogenesis in autoimmune diseases and allergy. However, the immune disorder fails to be cured and induces the relapse. The repeated pathogenesis is provided by memory cells including memory Th cells, memory B cells and/or long-lived (memory) plasma cells. To cure autoimmune diseases, we have to deplete all memory cell populations. Memory B cells and memory plasma cells can be depleted. However, memory Th cells failed to be depleted, because it remained unclear where and how memory Th cells are maintained. Ten years ago, we showed that most memory Th cells reside and rest in the BM stromal cells (Tokoyoda et al., Immunity 2009). We then tried to determine how they are maintained in this project. We here show that splenic memory Th cells are maintained in an IL-7-dependent manner and BM memory Th cells are maintained in a CD49b-dependent manner. To deplete all memory Th cells, we have to target both types of memory Th cells. The involvement of IL-7 and CD49b was expected in the proposal. However, the finding on the role of regulatory T cells was unexpected but highly impressed. Furthermore, we found that regulatory T cells support the expression of collagens (CD49b ligand) and IL-7 in BM stromal cells. The depletion of regulatory T cells reduces the expression of collagens and IL-7 and then reduces both memory Th cells. Since memory Th cells are the main source of IL-2, a survival factor of regulatory T cells, we suggest that memory Th cells, regulatory T cells and stromal cells support each other. The project has been successfully completed according to the original proposal. It is a novel finding that resting BM memory Th cells are maintained by adhesion signal and active splenic memory Th cells are maintained by cytokine signal. Two different signals provide distinct cell status, characteristics and function. In addition, we could show a systemic cooperative mechanism among three cell populations, memory Th cells, regulatory T cells and stromal cells in the BM. These finding greatly contributes to the development of immunological memory field for basic and clinic studies.

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