Londregan, J. | bioRxiv Science

bioRxiv2025

Notch2 signaling instructs viral and bacterial TLR responsiveness in B cells

Marginal zone (MZ) B cells are hyperresponsive to bacterial Toll-like Receptor (TLR) ligands. However, the full extent of TLR responsiveness for MZ B cells and the mechanisms regulating such responses are unclear. We report that Notch2 activation establishes MZ B cell responsiveness for the viral dsRNA receptor TLR3 and augments responses for the LPS receptor TLR4. Notch2 ligation accelerated Myc induction, mitosis, and plasma cell differentiation to LPS. Further, TLR3 expression in MZ B cells was Notch2 dependent, and ectopic Notch2 signaling was sufficient to promote robust TLR3 responsiveness dependent on the TIR-domain-containing adapter TRIF and the kinase BTK. TLR3 engagement in MZ B cells promoted proliferation, differentiation, and the secretion of IgG2b and IgG2c antibodies. Our results establish a novel role for Notch2 in establishing TLR3 and TLR4 responsiveness in B cells and suggest that MZ B cells play unappreciated roles in immunity against RNA viruses.

immunology↗

bioRxiv2025

Clostridioides difficile toxin A and toxin B inhibit toxin-specific adaptive immune responses through glucosyltransferase-dependent activity

Clostridioides difficile colonizes the gastrointestinal tract and secretes two virulence factors: toxin A (TcdA) and toxin B (TcdB). Protective immunity against C. difficile infection is limited as patients are susceptible to multiple rounds of recurrent infections. The factors determining whether immunity to TcdA and TcdB is generated remain incompletely defined. We determined that C. difficile-infected mice generate antibody and IL-17A-producing CD4+ T cell responses to TcdA, but not TcdB. To determine the mechanism of the failed anti-TcdB immunity, C. difficile mutant strains expressing glucosyltransferase inactive (GTX) TcdA, and/or glucosyltransferase inactive TcdB were used. Infection with TcdBGTX or dual mutant (TcdAGTX TcdBGTX) restored TcdB-specific antibody responses, while infection with TcdAGTX or TcdAGTX TcdBGTX led to an earlier induction of TcdA-specific antibodies. Finally, infection with the dual GTX mutant enhanced TcdA and TcdB-specific CD4+ T cell responses. These data demonstrate that the glucosyltransferase activity of TcdA and TcdB hinders the antigen-specific adaptive immune response to itself and may be a mechanism that underlies high recurrence rates following C. difficile infection in patients.

immunology↗