Taming AID mutator activity in somatic hypermutation

Interleukin-37 Suppresses the Function of Type 2 Follicular Helper T in Allergic Rhinitis

Background: Allergic rhinitis (AR) is triggered by immunoglobulin E (IgE)-mediated immune responses to airborne allergens. Recent studies highlight the pivotal role of T follicular helper 2 (Tfh2) cells in IgE production. Interleukin-37 (IL-37) has emerged as an intrinsic modulator of innate immunity and inflammatory processes. We aimed to investigate the regulatory effect of IL-37 on Tfh2 cells in the pathogenesis of AR. Methods: Blood samples were collected from AR patients and controls. The IL-37 levels and the frequency of Tfh2 cells were detected by enzyme-linked immunosorbent assay (ELISA) and flow cytometry, respectively. The isolated Tfh2 cells were cultured or cocultured with naive B cells. The regulatory effects of IL-37 on Tfh2/B cells were assessed using ELISA, quantitative real-time polymerase chain reaction (qRT-PCR). Mouse models of ovalbumin (OVA)-induced AR were established to explore the effect of IL-37 in vivo. Results: IL-37 suppressed the production of IL-4 and IL-21 by Tfh2 cells and downregulated C-X-C chemokine receptor type 5 (CXCR5) and B-cell lymphoma 6 protein (Bcl6) mRNA expression while upregulating B lymphocyte-induced maturation protein 1 (Blimp1) and signal transducers and activators of transduction5 (STAT5) mRNA. IL-37 decreased IgE production by B cells significantly, and the addition of anti-IL-18 receptor α alleviated this effect. In mouse models, IL-37 reduced nasal rubbing, sneezing, eosinophil counts, OVA-specific IgE, and Tfh2 proportions. Conclusions: IL-37 plays a crucial role in modulating Tfh2 cell responses in AR, suggesting a potential therapeutic target for this condition.

Molecular mechanisms of DNA lesion and repair during antibody somatic hypermutation

Antibody diversification is essential for an effective immune response, with somatic hypermutation (SHM) serving as a key molecular process in this adaptation. Activation-induced cytidine deaminase (AID) initiates SHM by inducing DNA lesions, which are ultimately resolved into point mutations, as well as small insertions and deletions (indels). These mutational outcomes contribute to antibody affinity maturation. The mechanisms responsible for generating point mutations and indels involve the base excision repair (BER) and mismatch repair (MMR) pathways, which are well coordinated to maintain genomic integrity while allowing for beneficial mutations to occur. In this regard, translesion synthesis (TLS) polymerases contribute to the diversity of mutational outcomes in antibody genes by enabling the bypass of DNA lesions. This review summarizes our current understanding of the distinct molecular mechanisms that generate point mutations and indels during SHM. Understanding these mechanisms is critical for elucidating the development of broadly neutralizing antibodies (bnAbs) and autoantibodies, and has implications for vaccine design and therapeutics.