Dissecting the protective and pathogenic functions of Tbet+CD11c+ B cells in differing inflammatory environments

About This Grant

Project Summary Follicular B cells have two developmental pathway options upon activation: the canonical germinal center pathway and the extrafollicular pathway. The germinal center is a key microanatomical structure in which B cells undergo stringent selection and mutation, resulting in a pool of B cells with high-affinity for the initiating foreign antigen and little to no autoreactive B cell clones. On the other hand, B cells that enter the extrafollicular pathway do not undergo stringent selection and therefore can result in not only the activation of foreign antigen-specific B cells but also self-reactive B cell clones. It has been demonstrated, by our lab and others, that a unique type of extrafollicular B cell has the capacity to produce both protective and pathogenic antibodies. This B cell compartment, composed of B cells that co-express Tbet and CD11c, plays a key role in the protection against many bloodborne pathogens but also has been implicated in the progression of autoimmune diseases. While antibodies from Tbet+CD11c+ B cells are mutated, these cells, in the context of acute infection, do not enter the germinal center reaction. It is unknown whether or not Tbet+CD11c+ B cells have the capacity to enter the germinal center during differing inflammatory environments, and whether the Tbet+CD11c+ B cell compartment is comprised of two independent pools, one with protective functions or one with pathogenic functions, or if the compartment is comprised of polyreactive Tbet+CD11c+ B cells. We hypothesize that Tbet+CD11c+ B cells have germline BCR sequences that allow for the recognition for both viral and self-antigen and that, due to a decrease in selection pressure experienced by extrafollicular B cells, Tbet+CD11c+ B cells that recognize both types of antigens are able to expand and participate in the immune response regardless of the initiating stimulus and inflammatory environment. My first aim is to uncover the basis for Tbet+CD11c+ autoreactivity during acute viral infection. To determine this, I will sequence viral antigen-specific Tbet+CD11c+ B cells, reexpress their immunoglobulin (Ig) sequences, and test their reactivity to self-antigen. I will also revert their sequences back to germline, reexpress the germline Ig sequences, and determine if the autoreactivity is retained. My second aim is to uncover how the autoreactive B cell pool differs under unique inflammatory environments. To this end, I will determine the contribution of Tbet+CD11c+ B cells to the autoreactive pool during chronic viral infection and chronic inflammation in the absence of virus using flow cytometry, determining antibody specificities, and investigating if Tbet+CD11c+ B cells contribute to the germinal center reaction during chronic inflammation using transgenic mice models and single-cell B cell receptor signaling. If successful, my project will uncover a key relationship between protective and pathogenic B cells. Moreover, my project will help elucidate how the behavior of extrafollicular B cells is influenced by its surround environment.