The NF-kappaB canonical pathway is involved in the control of the exonucleolytic processing of coding ends during V(D)J recombination

Immunoglobulin class-switch recombination: Mechanism, regulation, and related diseases

Maturation of the secondary antibody repertoire requires class-switch recombination (CSR), which switches IgM to other immunoglobulins (Igs), and somatic hypermutation, which promotes the production of high-affinity antibodies. Following immune response or infection within the body, activation of T cell-dependent and T cell-independent antigens triggers the activation of activation-induced cytidine deaminase, initiating the CSR process. CSR has the capacity to modify the functional properties of antibodies, thereby contributing to the adaptive immune response in the organism. Ig CSR defects, characterized by an abnormal relative frequency of Ig isotypes, represent a rare form of primary immunodeficiency. Elucidating the molecular basis of Ig diversification is essential for a better understanding of diseases related to Ig CSR defects and could provide clues for clinical diagnosis and therapeutic approaches. Here, we review the most recent insights on the diversification of five Ig isotypes and choose several classic diseases, including hyper-IgM syndrome, Waldenström macroglobulinemia, hyper-IgD syndrome, selective IgA deficiency, hyper-IgE syndrome, multiple myeloma, and Burkitt lymphoma, to illustrate the mechanism of Ig CSR deficiency. The investigation into the underlying mechanism of Ig CSR holds significant potential for the advancement of increasingly precise diagnostic and therapeutic approaches.

Targeting NF-κB pathway for the therapy of diseases: mechanism and clinical study

NF-κB pathway consists of canonical and non-canonical pathways. The canonical NF-κB is activated by various stimuli, transducing a quick but transient transcriptional activity, to regulate the expression of various proinflammatory genes and also serve as the critical mediator for inflammatory response. Meanwhile, the activation of the non-canonical NF-κB pathway occurs through a handful of TNF receptor superfamily members. Since the activation of this pathway involves protein synthesis, the kinetics of non-canonical NF-κB activation is slow but persistent, in concordance with its biological functions in the development of immune cell and lymphoid organ, immune homeostasis and immune response. The activation of the canonical and non-canonical NF-κB pathway is tightly controlled, highlighting the vital roles of ubiquitination in these pathways. Emerging studies indicate that dysregulated NF-κB activity causes inflammation-related diseases as well as cancers, and NF-κB has been long proposed as the potential target for therapy of diseases. This review attempts to summarize our current knowledge and updates on the mechanisms of NF-κB pathway regulation and the potential therapeutic application of inhibition of NF-κB signaling in cancer and inflammatory diseases.

Characteristics of Plasmablast Repertoire in Chronically HIV-Infected Individuals for Immunoglobulin H and L Chain Profiled by Single-Cell Analysis

Characterization of the diversified immunoglobulin (Ig) repertoire may provide insight into pathways that shape an efficient antibody (Ab) repertoire for immune response against human immunodeficiency virus (HIV) infection. This study aimed to profile characteristics of the plasmablast repertoire during chronic HIV infection. Ig variable regions of plasmablasts from both chronically HIV-infected donors (HIVDs) previously treated with antiretroviral therapy (ART) and healthy donors (HDs) were amplified by single-cell PCR to establish the basis for further repertoire analysis. We compared the plasmablast repertoires expressed in multiple chronically HIVDs after ART treatment cessation and HDs. We also examined the non-productive repertoire to identify the indication of the immediate products of the rearrangement machinery without an impact of selection during HIV infection. We found multiple differences between the productive repertoires of HIVD and HD subjects, including biased usages of VH3-49, VH1-2, VH3-33, VH3-74, and VH5-51 in VH and D1-7, D1-14, D1-20, and D5-5/18 in D segments in the HIVD group, as well as shorter and preferential glycine usages in CDRH3 regions. Gene selections were also detected in light chains. Notably, differences between productive rearrangements of HIVDs and HDs outnumbered those between productive and non-productive rearrangements within HIVDs. HIV infection may exert a dominant impact on the development of the plasmablast repertoire. The impact of selection is of limited significance in shaping the plasmablast repertoire. Overall, the data indicate that the environment in which the plasmablasts live can affect the distribution of the VH and VL genes in the repertoire and the amino acid compositions of the expressed Abs.

The Role of the Nuclear Factor κB Pathway in the Cellular Response to Low and High Linear Energy Transfer Radiation

Astronauts are exposed to considerable doses of space radiation during long-term space missions. As complete shielding of the highly energetic particles is impracticable, the cellular response to space-relevant radiation qualities has to be understood in order to develop countermeasures and to reduce radiation risk uncertainties. The transcription factor Nuclear Factor κB (NF-κB) plays a fundamental role in the immune response and in the pathogenesis of many diseases. We have previously shown that heavy ions with a linear energy transfer (LET) of 100–300 keV/µm have a nine times higher potential to activate NF-κB compared to low-LET X-rays. Here, chemical inhibitor studies using human embryonic kidney cells (HEK) showed that the DNA damage sensor Ataxia telangiectasia mutated (ATM) and the proteasome were essential for NF-κB activation in response to X-rays and heavy ions. NF-κB’s role in cellular radiation response was determined by stable knock-down of the NF-κB subunit RelA. Transfection of a RelA short-hairpin RNA plasmid resulted in higher sensitivity towards X-rays, but not towards heavy ions. Reverse Transcriptase real-time quantitative PCR (RT-qPCR) showed that after exposure to X-rays and heavy ions, NF-κB predominantly upregulates genes involved in intercellular communication processes. This process is strictly NF-κB dependent as the response is completely absent in RelA knock-down cells. NF-κB’s role in the cellular radiation response depends on the radiation quality.

Mechanisms That Shape Human Antibody Repertoire Development in Mice Transgenic for Human Ig H and L Chain Loci

To determine the impact of the milieu on the development of the human B cell repertoire, we carried out a comprehensive analysis of productive and nonproductive Ig gene rearrangements from transgenic mice engineered to express single copies of the unrearranged human H chain and L chain Ig gene loci. By examining the nonproductive repertoire as an indication of the immediate product of the rearrangement machinery without an impact of selection, we discovered that the distribution of human rearrangements arising in the mouse was generally comparable to that seen in humans. However, differences between the distribution of nonproductive and productive rearrangements that reflect the impact of selection suggested species-specific selection played a role in shaping the respective repertoires. Although expression of some VH genes was similar in mouse and human (IGHV3-23, IGHV3-30, and IGHV4-59), other genes behaved differently (IGHV3-33, IGHV3-48, IGHV4-31, IGHV4-34, and IGHV1-18). Gene selection differences were also noted in L chains. Notably, nonproductive human VH rearrangements in the transgenic mice expressed shorter CDRH3 with less N addition. Even the CDRH3s in the productive rearrangements were shorter in length than those of the normal human productive repertoire. Amino acids in the CDRH3s in both species showed positive selection of tyrosines and glycines, and negative selection of leucines. The data indicate that the environment in which B cells develop can affect the expressed Ig repertoire by exerting influences on the distribution of expressed VH and VL genes and by influencing the amino acid composition of the Ag binding site.

V(D)J recombination process and the Pre-B to immature B-cells transition are altered in Fanca-/- mice

B-lymphocytes in the bone marrow (BM) must generate a functional B-cell receptor and overcome the negative selection induced by reactivity with autoantigens. Two rounds of DNA recombination are required for the production of functional immunoglobulin heavy (Ig-HCs) and light (LCs) chains necessary for the continuation of B-lymphocyte development in the BM. Both rounds depend on the joint action of recombination activating gene-1 (RAG-1) and RAG-2 endonucleases with the DNA non-homologous end-joining pathway. Loss of the FANC gene leads to the chromosome breakage and cancer predisposition syndrome Fanconi anemia. Because the FANC proteins are involved in certain aspects of the recombination process, we sought to determine the impact of the FANC pathway on the Ig diversification process using Fanca^−/− mice. In this work we demonstrated that Fanca^−/− animals have a mild B-cell differentiation defect characterized by a specific alteration of the IgM⁻ to IgM⁺ transition of the B220^low B-cell population. Pre-B cells from Fanca^−/− mice show evidence of impaired kLC rearrangement at the level of the Vk-Jk junction. Furthermore, Fanca^−/− mice showed a skewed Vκ gene usage during formation of the LCs Vk-Jk junctions. Therefore, the Fanca protein appears as a yet unidentified factor involved in the primary diversification of Ig.

NF-κB regulates DNA double-strand break repair in conjunction with BRCA1-CtIP complexes

NF-κB is involved in immune responses, inflammation, oncogenesis, cell proliferation and apoptosis. Even though NF-κB can be activated by DNA damage via Ataxia telangiectasia-mutated (ATM) signalling, little was known about an involvement in DNA repair. In this work, we dissected distinct DNA double-strand break (DSB) repair mechanisms revealing a stimulatory role of NF-κB in homologous recombination (HR). This effect was independent of chromatin context, cell cycle distribution or cross-talk with p53. It was not mediated by the transcriptional NF-κB targets Bcl2, BAX or Ku70, known for their dual roles in apoptosis and DSB repair. A contribution by Bcl-xL was abrogated when caspases were inhibited. Notably, HR induction by NF-κB required the targets ATM and BRCA2. Additionally, we provide evidence that NF-κB interacts with CtIP-BRCA1 complexes and promotes BRCA1 stabilization, and thereby contributes to HR induction. Immunofluorescence analysis revealed accelerated formation of replication protein A (RPA) and Rad51 foci upon NF-κB activation indicating HR stimulation through DSB resection by the interacting CtIP-BRCA1 complex and Rad51 filament formation. Taken together, these results define multiple NF-κB-dependent mechanisms regulating HR induction, and thereby providing a novel intriguing explanation for both NF-κB-mediated resistance to chemo- and radiotherapies as well as for the sensitization by pharmaceutical intervention of NF-κB activation.

Decreased expression in nuclear factor-κB essential modulator due to a novel splice-site mutation causes X-linked ectodermal dysplasia with immunodeficiency

X-linked ectodermal dysplasia with immunodeficiency (XL-ED-ID) is caused by hypomorphic mutations in NEMO, which encodes nuclear factor-kappaB (NF-κB) essential modulator. We identified a novel mutation, 769-1 G>C, at the splicing acceptor site of exon 7 in NEMO in a Japanese patient with XL-ED-ID. Although various abnormally spliced NEMO messenger RNAs (mRNAs) were observed, a small amount of wild-type (WT) mRNA was also identified. Decreased NEMO protein expression was detected in various lineages of leukocytes. Although one abnormally spliced NEMO protein showed residual NF-κB transcription activity, it did not seem to exert a dominant-negative effect against WT-NEMO activity. CD4(+) T cell proliferation was impaired in response to measles and mumps, but not rubella. These results were consistent with the clinical and laboratory findings of the patient, suggesting the functional importance of NEMO against specific viral infections. The 769-1 G>C mutation is responsible for decreased WT-NEMO protein expression, resulting in the development of XL-ED-ID.

Recovering probabilities for nucleotide trimming processes for T cell receptor TRA and TRG V-J junctions analyzed with IMGT tools

Background

Nucleotides are trimmed from the ends of variable (V), diversity (D) and joining (J) genes during immunoglobulin (IG) and T cell receptor (TR) rearrangements in B cells and T cells of the immune system. This trimming is followed by addition of nucleotides at random, forming the N regions (N for nucleotides) of the V-J and V-D-J junctions. These processes are crucial for creating diversity in the immune response since the number of trimmed nucleotides and the number of added nucleotides vary in each B or T cell. IMGT^® sequence analysis tools, IMGT/V-QUEST and IMGT/JunctionAnalysis, are able to provide detailed and accurate analysis of the final observed junction nucleotide sequences (tool "output"). However, as trimmed nucleotides can potentially be replaced by identical N region nucleotides during the process, the observed "output" represents a biased estimate of the "true trimming process."

Results

A probabilistic approach based on an analysis of the standardized tool "output" is proposed to infer the probability distribution of the "true trimmming process" and to provide plausible biological hypotheses explaining this process. We collated a benchmark dataset of TR alpha (TRA) and TR gamma (TRG) V-J rearranged sequences and junctions analysed with IMGT/V-QUEST and IMGT/JunctionAnalysis, the nucleotide sequence analysis tools from IMGT^®, the international ImMunoGeneTics information system^®, . The standardized description of the tool output is based on the IMGT-ONTOLOGY axioms and concepts. We propose a simple first-order model that attempts to transform the observed "output" probability distribution into an estimate closer to the "true trimming process" probability distribution. We use this estimate to test the hypothesis that Poisson processes are involved in trimming. This hypothesis was not rejected at standard confidence levels for three of the four trimming processes: TRAV, TRAJ and TRGV.

Conclusion

By using trimming of rearranged TR genes as a benchmark, we show that a probabilistic approach, applied to IMGT^® standardized tool "outputs" opens the way to plausible hypotheses on the events involved in the "true trimming process" and eventually to an exact quantification of trimming itself. With increasing high-throughput of standardized immunogenetics data, similar probabilistic approaches will improve understanding of processes so far only characterized by the "output" of standardized tools.

From infectious diseases to primary immunodeficiencies

The field of primary immunodeficiencies has expanded, thanks to the exploration of novel clinical phenotypes and their connection with morbid genotypes, and the subsequent exploration of new patients who have known primary immunodeficiency-defining clinical phenotypes and their connection with novel morbid genotypes. This two-way process is becoming increasingly active, particularly for patients who have infectious diseases in whom the underlying immunologic and genetic causes remain mostly unexplained. The authors review how the exploration of children who have clinical infectious diseases caused by mycobacteria, pneumococcus, and herpes simplex virus recently led to the description of three new groups of primary immunodeficiencies. These three examples justify the continuation of the genetic exploration of novel infectious phenotypes and novel patients who have infections. This challenging process will eventually reap its rewards, to the benefit of patients and their families.