IL-27-producing B cells in the antibody response

PROJECT SUMMARY - IL-27-producing B cells in the antibody response Built on our novel findings that B cells can be induced to express high levels of IL-27 (IL27p28/EBI3 heterodimer), this proposal will explore molecular and cellular mechanisms underlying the role of IL-27 and IL-27-producing B cells (B-27 cells) in class-switched antibody (Ab) responses. As we contend, B-27 cells shape the magnitude and quality of T-dependent Ab responses, including those elicited by viral infections. As we also contend, they do so as "helper" B cells to enhance the function of their target "effector" B cells, i.e., those responding to antigens and differentiating into IgG-producing cells. Such class-switched Abs include IgG1, which directly neutralizes virus, and human IgG3 and mouse IgG2a/IgG2c (IgG2a), which have additional anti-viral effector functions. Owing to the unique requirement of both innate and adaptive immune receptor signals for their induction, B-27 cells are strategically positioned to mediate the potent effect of TLR ligands in boosting the Ab response. We hypothesize that B-27 cells are induced in a manner dependent on transcription factor BATF3, and optimize the Ab response by cooperating with IFNg to promote proliferation, survival and full differentiation of IgG-producing B cells. This is based on our compelling preliminary data indicating that: (i) as an important source of IL-27, B cells are induced to produce IL-27 after priming by TLR ligands and then stimulation by Tfh cell stimuli CD154 and IL-21; (ii) mice with B cell-specific deficiency in Il27p28, Ebi3 or Batf3 are impaired in IL-27 production and specific IgG2a responses; (iii) IL-27 activates STATs, directs CSR to IgG2a and promotes survival and plasma cell differentiation in B cells stimulated by CD154 and IL-21 in vitro; and (iv) IL-27 and IFNg together boost B cell growth and differentiation in vitro, and, conversely, combined IL-27R and IFNgR deficiency in B cells abrogates specific IgG2a responses and significantly impairs IgG1 responses in vivo. To test our hypothesis, we will (Aim 1) characterize B-27 cells induced in Tg(Il27p28-Gfp) reporter mice upon infection by vaccinia virus (VV), which is also used as a vector of a variety of vaccines, or immunization with conjugated hapten NP-CGG mixed with alum and TLR ligand LPS; and determine the cooperation of B-27 cells with IFNg in specific IgG responses and underlying effector B cell proliferation, survival, CSR/SHM, plasma cell and memory B cell differentiation. We will also (Aim 2) address the mechanisms underlying the role of BATF3 in Il27p28 induction by identifying its cis-elements in the Il27p28 locus and partner transcription factors in vitro; and analyze induction of B cell BATF3 and its impact on B-27 cell generation and Ab responses to VV infection and NP-CGG/alum/LPS in vivo. Finally, we will (Aim 3) analyze the cooperation of B-cell IL-27R and IFNgR signals in optimizing effector B cell growth and differentiation in response to VV infection in vivo and stimulation with CD154 and IL-21 in vitro; and address the underlying mechanisms, focusing on their synergy in regulating STAT signal outputs and gene expression. By unveiling the mechanisms and function of B-27 cells, our studies will have a sustained impact on the understanding of IgG responses to viral infections and vaccine development.