Defining the role of toll-like receptor 10 in immune signaling

Toll-like Receptors (TLRs) represent a class of pattern recognition receptors that function to recognize invading microbes and initiate pro-inflammatory responses. TLR10 is the only remaining orphan member of the human TLR family. Given the established role of TLR signaling in both the innate and adaptive arms of immune defense, defining the function of TLR10 in the immune response would fill a significant knowledge gap regarding the question of why the gene has been propagated through evolutionary history. Additionally, given the growing recognition of the impact of TLR biology on human disease, additional knowledge of this orphan TLR may also provide a novel therapeutic target. Chapter One of this dissertation introduces the main events that occur in the innate and adaptive immune responses to infection and describes the role of TLRs in the induction and propagation of such responses. It also highlights the growing recognition of lymphocyte-intrinsic TLR signaling and its role in robust adaptive immune responses. Lastly, it provides background information on what is known about TLR10 currently and identifies the knowledge gap that this research seeks to fill. Chapter Two describes the capacity of TLR10 to act as a general suppressor of pro-inflammatory TLR signaling. Given the lack of TLR10 expression in mice, heterologous expression of TLR10 in cell lines and transgenic mice was used, and these studies revealed an inhibitory role for TLR10 in the context of pro-inflammatory cellular responses to numerous TLR ligands. The effect of TLR10 in abrogating both MyD88 and TRIF dependent signaling was discovered using transient transfection techniques. Lastly, ligation of cell surface TLR10 in whole blood using a monoclonal antibody resulted in strongly attenuated responses to TLR agonists (Jiang et al. 2016). Chapter Three focuses on the expression of surface TLR10 within the B cell lineage. While numerous studies have shown the presence of TLR10 mRNA in cell lines and primary cells, the lack of a reliable commercially available antibody to TLR10 prevented careful investigation of cell surface expression of TLR10 protein. A monoclonal antibody created in the lab was used to investigate the regulation of TLR10 expression in blood leukocytes and tonsillar tissue. This led to the validation that significant levels of TLR10 are present on CD19+ B cells and that this surface expression is attenuated along progressive stages of B cell activation within lymphoid tissue. Chapter Four presents studies investigating the role of TLR10 in the context of B cell activation. I found that stimulation of TLR10 in human peripheral blood B cells results in strongly attenuated B cell proliferation, cytokine production, and induction of B cell activation genes. Additionally, I observed a subtle effect on B cell signaling events via phosphorylation of B cell signaling molecules. These findings are further corroborated with concurrent transgenic mouse studies that reveal profound suppressive effects of TLR10 on switched antibody production, performed by Dr. Xinyan Li and Nick Hess, that are also presented in this chapter. Chapter Five draws together the findings on the function of TLR10 and offers insight on the potential role of TLR10 in B cell biology. In addition, the chapter highlights future directions and questions, which remain to be answered, that would further advance knowledge of the signaling function of TLR10 and its potential as a therapeutic target for autoimmune diseases and hematologic malignancies