Oral Presentation Lorne Infection and Immunity 2019

Transcription factor T-bet in B cells controls germinal centre dark zone-light zone polarization and enhances antibody affinity maturation in response to malaria     (#27)

Ann Ly 1 , Yang Liao 1 , Halina Piertzak 1 , Lisa Ioannidis 1 , Tony Triglia 1 , Kim Good-Jacobson 2 , Wei Shi 1 , Axel Kallies 3 , Diana S Hansen 1
  1. Walter and Eliza Hall Institute of Medical Research, Parkville, VIC, Australia
  2. Department of Biochemistry and Molecular Biology, Monash University, Clayton, Victoria, Australia
  3. Department of Microbiology and Immunology, The Peter Doherty Institute for Infection and Immunity, Melbourne, Victoria, Australia

Despite the key role that antibodies play in protection against malaria, the cellular processes underlying the slow acquisition of immunity are not fully understood. Using the P. berghei ANKA model, we previously found that inflammatory cytokines associated with clinical malaria inhibit TFH cell differentiation, resulting in the accumulation of TFH precursors that express the TH1-defining transcription factor T-bet. Genetic deletion of T-bet restored TFH cell differentiation and GC B cell responses. As T-bet has been also found to be expressed in B cells we sought to determine if the enhanced GC response observed in the absence of T-bet reflected solely improved helper activity and/or intrinsic changes in B cell function. For that, Tbx21fl/flCd23Cre mice, which lack T-bet in mature B cells, were infected with P. berghei ANKA and GC responses were examined. We found that intrinsic expression of T-bet in B cells was required for IgG2c switching but diminished the magnitude of GC B cell responses. RNA-sequencing and flow cytometry analysis of Tbx21fl/flCd23Cre and Cd23Cre/+ GC B cells revealed that T-bet is required for commitment of B cells to the GC dark zone (DZ), thereby significantly influencing DZ/light zone (LZ) polarization. Consistently, Tbx21fl/flCd23Cre mice displayed significantly reduced mutation frequencies in their IghV genes and lower antibody affinity than controls indicating that T-bet is critical for Ig affinity maturation. These results demonstrate that although T-bet moderates the magnitude of the GC response, it also promotes efficient GC dynamics, thereby preventing the premature exit of B cells from the GC reaction and leading to the differentiation of antigen-experienced B cells with increased affinity for antigen required for efficient control of infection.