Antigen Complexed with a TLR9 Agonist Bolsters c-Myc and mTORC1 Activity in Germinal Center B Lymphocytes

Abstract

The germinal center (GC) is the anatomical site where humoral immunity evolves. B cells undergo cycles of proliferation and selection to produce high-affinity Abs against Ag. Direct linkage of a TLR9 agonist (CpG) to a T-dependent Ag increases the number of GC B cells. We used a T-dependent Ag complexed with CpG and a genetic model for ablating the TLR9 signaling adaptor molecule MyD88 specifically in B cells (B-MyD88 2 mice) together with transcriptomics to determine how this innate pathway positively regulates the GC. GC B cells from complex Ag-immunized B-MyD88 2 mice were defective in inducing gene expression signatures downstream of c-Myc and mTORC1. In agreement with the latter gene signature, ribosomal protein S6 phosphorylation was increased in GC B cells from wild-type mice compared with B-MyD88 2 mice. However, GC B cell expression of a c-Myc protein reporter was enhanced by CpG attached to Ag in both wild-type and B-MyD88 2 mice, indicating a B cell-extrinsic effect on c-Myc protein expression combined with a B cell-intrinsic enhancement of gene expression downstream of c-Myc. Both mTORC1 activity and c-Myc are directly induced by T cell help, indicating that TLR9 signaling in GC B cells either enhances their access to T cell help or directly influences these pathways to further enhance the effect of T cell help. Taken together, these findings indicate that TLR9 signaling in the GC could provide a surrogate prosurvival stimulus, "TLR help," thus lowering the threshold for selection and increasing the magnitude of the GC response. ImmunoHorizons, 2019, 3: 389-401.

Synthetic Liposomal Mimics of Biological Viruses for the Study of Immune Responses to Infection and Vaccination

“…Nucleic acids are highly immunostimulatory molecules that can be recognized by both endosomal and cytosolic sensors in B cells and can trigger B-cell activation both independently of and synergistically with B-cell antigen receptor (BCR) engagement . Importantly, differences in the site and context in which nucleic acids are sensed by B cells can have profoundly divergent effects on B-cell responses. , Therefore, in order to accurately model the immune responses of B cells toward particulate antigens such as naturally occurring viruses, it is critical to produce synthetic particles that mimic both of these essential features of a viral particle. In order to study these aspects in isolation and collectively, it is ideal for these features to be independently built into a model antigen.…”

Early reappearance of intraclonal proliferative subpopulations in ibrutinib-resistant chronic lymphocytic leukemia

“…The presence of a coordinated signals through TLR9 has been reported in other lymphoproliferative diseases [74], where BCR and TLR9 actively cooperate to activate NF-κB. Therefore it can be speculated that CLL cells, after prolonged inhibition of BCR by ibrutinib, may try to adapt to different stimuli that provide the same pro-survival signals [70,75,76]. In this context, an unaddressed issue remains the responsiveness of the proliferative compartment to newer-generation BTK inhibitors, which provide better and longer remissions; of note, a single CLL patient (TS208) with high PF at progression, treated with pirtobrutinib for over a year, showed a rapid and stable loss of the PF (FP and AZ, personal observation).…”

“…Indeed, when evaluating if different signaling programs may characterize ibrutinib-resistant BTK-unmutated CLL, we could detect a more frequent usage of MYC signaling along with TLR9 signaling. In this regard, BTK-unmutated CLL cells, whose BCR signaling is still inhibited by ibrutinib, may try to compensate the decrease of pro-survival signals no longer gained through the BCR pathway by activating other pathways, including MYC and/or TLR9 [69][70][71][72][73]. The presence of a coordinated signals through TLR9 has been reported in other lymphoproliferative diseases [74], where BCR and TLR9 actively cooperate to activate NF-κB.…”