Search Results (4)

Background: N-glycosylation is a post-translational modification involving the attachment of oligosaccharides to proteins and is known to influence immunoglobulin G (IgG) effector functions and even antigen binding. IgG contains an evolutionarily conserved N-glycosylation site in its fragment crystallizable (Fc) region, while during V-D-J recombination and somatic hypermutation processes it can also obtain N-glycosylation sites in its antigen binding fragment (Fab). Our previous study demonstrated altered IgG N-glycosylation in children at type 1 diabetes (T1D) onset, with the most prominent changes involving sialylated glycans, hypothesized to mainly come from the Fab region, however, the analytical method used could not distinguish between Fc and Fab. Methods: IgG was isolated from plasma from 118 children with T1D and 98 healthy controls from the Danish Registry of Childhood and Adolescent Diabetes. Isolated IgG was cleaved into Fc and Fab fragments using IdeS enzyme. N-glycans were enzymatically released from each fragment, fluorescently labelled with procainamide, and analyzed separately using the UPLC-MS method. Structural annotation of resulting chromatograms was performed using MS/MS. Results: T1D related N-glycosylation changes were more pronounced in the Fab glycans compared to Fc glycans, with five Fab glycans (Man5, Man7, FA2BG1S1, A2G2S2, FA2BG2S1) being significantly altered compared to only one in the Fc region (FA2[3]BG1). Comparing Fc and Fab glycosylation overall reveals stark differences in the types of glycans on each region, with a more diverse and complex repertoire being present in the Fab region. Conclusions: These findings suggest that N-glycosylation changes in early onset T1D predominantly originate from the Fab region, underscoring their potential role in modulating (auto)immunity and highlighting distinct glycosylation patterns between Fc and Fab. Full article

B lymphocyte development has two DNA recombination processes: V(D)J recombination of the immunoglobulin (Igh) gene variable region, and class switching of the Igh constant regions from IgM to IgG, IgA, or IgE. V(D)J recombination is required for the successful maturation of B cells from pro-B to pre-B to immature-B and then to mature B cells in the bone marrow. CSR occurs outside of the bone marrow when mature B cells migrate to peripheral lymphoid organs, such as spleen and lymph nodes. Both V(D)J recombination and CSR depend on an open chromatin state that makes DNA accessible to specific enzymes, recombination activating gene (RAG), and activation-induced cytidine deaminase (AID). Acetyltransferases GCN5 and PCAF possess redundant functions acetylating histone H3 lysine 9 (H3K9). Here, we generated a mouse model that lacked both GCN5 and PCAF in B cells. Double-deficient mice possessed low levels of mature B cells in the bone marrow and peripheral organs, an accumulation of pro-B cells in bone marrow, and reduced CSR levels. We concluded that both GCN5 and PCAF are required for B-cell development in vivo. Full article

Adaptive immunity relies on the V(D)J DNA recombination of immunoglobulin (Ig) and T cell receptor (TCR) genes, which enables the recognition of highly diverse antigens and the elicitation of antigen-specific immune responses. This process is mediated by recombination-activating gene (Rag) 1 and Rag2 (Rag1/2), whose expression is strictly controlled in a cell type-specific manner; the expression of Rag1/2 genes represents a hallmark of lymphoid lineage commitment. Although Rag genes are known to be evolutionally conserved among jawed vertebrates, how Rag genes are regulated by lineage-specific transcription factors (TFs) and how their regulatory system evolved among vertebrates have not been fully elucidated. Here, we reviewed the current body of knowledge concerning the cis-regulatory elements (CREs) of Rag genes and the evolution of the basic helix-loop-helix TF E protein regulating Rag gene CREs, as well as the evolution of the antagonist of this protein, the Id protein. This may help to understand how the adaptive immune system develops along with the evolution of responsible TFs and enhancers. Full article

Lymphocytes are endowed with unique and specialized enzymatic mutagenic properties that allow them to diversify their antigen receptors, which are crucial sensors for pathogens and mediators of adaptive immunity. During lymphocyte development, the antigen receptors expressed by B and T lymphocytes are assembled in an antigen-independent fashion by ordered variable gene segment recombinations (V(D)J recombination), which is a highly ordered and regulated process that requires the recombination activating gene products 1 & 2 (RAG1, RAG2). Upon activation by antigen, B lymphocytes undergo additional diversifications of their immunoglobulin B-cell receptors. Enzymatically induced somatic hypermutation (SHM) and immunoglobulin class switch recombination (CSR) improves the affinity for antigen and shape the effector function of the humoral immune response, respectively. The activation-induced cytidine deaminase (AID) enzyme is crucial for both SHM and CSR. These processes have evolved to both utilize as well as evade different DNA repair and DNA damage response pathways. The delicate balance between enzymatic mutagenesis and DNA repair is crucial for effective immune responses and the maintenance of genomic integrity. Not surprisingly, disturbances in this balance are at the basis of lymphoid malignancies by provoking the formation of oncogenic mutations and chromosomal aberrations. In this review, we discuss recent mechanistic insight into the regulation of RAG1/2 and AID expression and activity in lymphocytes and the complex interplay between these mutagenic enzymes and DNA repair and DNA damage response pathways, focusing on the base excision repair and mismatch repair pathways. We discuss how disturbances of this interplay induce genomic instability and contribute to oncogenesis. Full article