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Regulation of BCR-mediated Ca2+ mobilization by MIZ1-TIMBIM4 safeguards IgG1+ GC B cell positive selection

Zhang, L.; Toboso-Navasa, A.; Gunawan, A.; Camara, A.; Nakagawa, R.; Finsterbusch, K.; Chakravarty, P.; Newman, R.; Zhang, Y.; Eilers, M.; Wack, A.; Tolar, P.; Toellner, K.-M.; Calado, D. P.

2023-07-19 immunology
10.1101/2023.07.18.549490 bioRxiv
Show abstract

The transition from IgM to affinity-matured IgG antibodies is vital for effective humoral immunity. This is facilitated by germinal centers (GCs) through affinity maturation and preferential accumulation of IgG+ B cells over IgM+ B cells. However, it is not known whether the positive selection of the different immunoglobulin isotypes within GCs varies in its dependency on specific transcriptional mechanisms. Here, we identified IgG1+ GC B cell transcription factor dependency using CRISPR-Cas9 and conditional mouse genetics. We found that MIZ1 was specifically required for IgG1+ GC B cell survival during positive selection, whereas IgM+ GC B cells were largely independent. Mechanistically, MIZ1 induced TMBIM4, an ancestral anti-apoptotic protein that regulated inositol trisphosphate receptor mediated Ca2+ mobilization downstream of IgG1. The MIZ1-TMBIM4 axis prevented mitochondrial dysfunction-induced IgG1+ GC cell death caused by excessive Ca2+ accumulation. This study uncovers a unique immunoglobulin isotype-specific dependency, on a hitherto unidentified mechanism in GC positive selection.

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