Felix Marsh-Wakefield’s Quest in Defending the Human Race against Autoimmune Diseases using Mast cell-activated B Cells

Abstract

Exposure to the ultraviolet (UV) component of sunlight is immune suppressive. This contributes to skin cancers, but can also protect the host from autoimmune diseases, such as multiple sclerosis (MS). Understanding the mechanisms underlying UV-immunosuppression is therefore critical if we are to combat skin cancer, and develop new therapeutics for MS patients. Mast cells and regulatory B cells are essential for UV-immunosuppression. Furthermore, murine IL-4-treated mast cells activate functionally suppressive B cells via microvesicles. The data presented in this thesis will reveal how mast cells may activate B cells; potential mechanisms by which these B cells suppress immunity; and that a similar event occurs in humans. Intracellular flow cytometry found IL-4 upregulated mast cell-derived IL-13 and EBI3, but also IL-10 and p35 after co-culture with B cells. Although mast cells did not appear to affect B cell cytokine production, microvesicle-activated B cells were functionally suppressive in vivo. These B cells promoted mast cell-derived IL-13, suggesting a cross talk is occurring. Human mast cells were grown from CD34+ peripheral blood stem cells and stimulated with IL 4 before co-culture with autologous B cells. Mass cytometry revealed IL-4-treated mast cells (and their microvesicles) preferentially targeted CD23+ CD38+/hi IgMhi transitional B cells, promoting an immunoregulatory phenotype, with increased IL-10. Although other markers (such as CD25 and CD274) were upregulated, these B cells did not inhibit T cell proliferation. In fact, mast cell-activated B cells increased T cell proliferation. Despite this, IL 10 was increased in the culture supernatant, but only when microvesicle-activated B cells were co-cultured with T cells and mast cells, suggesting B cells require both mast cells and microvesicles to have a functional influence on T cells. The results presented in this thesis demonstrate the ability of mast cells and their microvesicles to activate regulatory B cells. These B cells in turn enhance mast cell cytokine production. Human mast cells activate B cells to have a regulatory phenotype. This study has provided further insight into mast cell-B cell interactions, and their importance in immune regulation. This has great implications in the study of carcinogenesis and autoimmune diseases.