Immunity to Trichuris muris: the role of B cells

  • Rinal Sahputra

Student thesis: Phd

Abstract

How B cells contribute to protective immunity against parasitic nematodes remains unclear, with their importance as regulatory cells under-explored. This study investigates the role of B cells in immunity to Trichuris muris (T. muris) infection using α-CD20 monoclonal antibody (Genentech-clone 5D2) to deplete B cells from two different mouse strains: C57BL/6 and BALB/c; and using the IgMi mouse in which B cells express IgM on their surface, but are unable to class switch or secrete antibodies. C57BL/6 mice receiving α-CD20 treatment prior to infection were susceptible to T. muris and Th2 type cytokines produced by mesenteric lymph nodes cells (MLNC) were significantly lower than produced by cells from isotype control treated mice. By contrast, BALB/c mice were still able to expel the worms in the absence of B cells. To explore whether the susceptibility of C57BL/6 mice after α-CD20 mAb treatment is due to the lack of B cells as antibody producers or as regulatory cells, IFN-γ was blocked using α-IFN-γ mAb post B cell depletion. Worm expulsion now occurred by day 21 post infection (p.i.) and the mice produced more T. muris specific IL-13, in the absence of T. muris specific antibody. To investigate whether B cells are important in initiating or maintaining Th2 type immune responses, B cells were depleted from day 14 p.i., culling mice at day 35 p.i. Surprisingly, removing B cells after two weeks post infection did not prevent worm expulsion, with the balance of Th1/Th2 cytokines remaining the same to as seen in isotype control treated mice. The IgMi mouse was first characterised in detail in the absence of infection. The data revealed that IgMi mice have significantly larger spleens and mesenteric lymph nodes (MLN) compared to WT littermates. Further, alterations in B1 cell subsets were evident in MLNs, spleen, and peritoneal cavity (PerC). CD103+CD11b+ DCs were significantly reduced in the IgMi MLN, whilst CD103+CD11b- DCs significantly increased in the IgMi spleen. Further, germinal centre (GC) B cells and T follicular helper (TFH) cells in the MLNs of IgMi mice were significantly increased. Interestingly, the lack of soluble antibodies, including IgA, in IgMi mice did not alter the gut microbiota compared to WT littermates. IgMi mice were susceptible to T. muris infection and MLNC from IgMi mice failed to produce Th2 type cytokines. MLNC from IgMi mice produced significantly higher levels of IL-10 compared to WT. Intracellular staining revealed that B cells were the main cellular source of IL-10 in IgMi mice. IgMi and WT littermate controls given a low dose T.muris infection both harboured similar worm burdens by day 50 p.i. Again, MLNC from IgMi mice produced significantly higher levels of IL-10. Further, IgMi mice also had significantly more apoptotic cells in the gut compared to WT. Collectively, this study suggests: (a) the importance of B cells in mediating worm expulsion during T. muris primary infection varies according to genetic background; (b) the important role played by B cells in resistance to infection is as a regulatory cell, acting to support Th2 type immune responses during the first two weeks post infection; (c) the high levels of IL-10 produced by IgMi B cells may be related to the lack of class-switched and/or secreted antibodies and may represent one way by which B cells promote susceptibility to infection in the IgMi mouse.
Date of Award1 Aug 2019
Original languageEnglish
Awarding Institution
  • The University of Manchester
SupervisorKathryn Else (Supervisor) & Andrew MacDonald (Supervisor)

Keywords

  • Interleukin 10
  • IgMi
  • T follicular helper
  • B cells
  • anti-CD20
  • Trichuris muris
  • Dendritic cells

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