The Anti-SARS-CoV-2 IgG1 and IgG3 Antibody Isotypes with Limited Neutralizing Capacity against Omicron Elicited in a Latin Population a Switch toward IgG4 after Multiple Doses with the mRNA Pfizer-BioNTech Vaccine

The aim of this study was to analyze the profiles of IgG subclasses in COVID-19 convalescent Puerto Rican subjects and compare these profiles with those of non-infected immunocompetent or immunocompromised subjects that received two or more doses of an mRNA vaccine. The most notable findings from this study are as follows: (1) Convalescent subjects that were not hospitalized developed high and long-lasting antibody responses. (2) Both IgG1 and IgG3 subclasses were more prevalent in the SARS-CoV-2-infected population, whereas IgG1 was more prevalent after vaccination. (3) Individuals that were infected and then later received two doses of an mRNA vaccine exhibited a more robust neutralizing capacity against Omicron than those that were never infected and received two doses of an mRNA vaccine. (4) A class switch toward the "anti-inflammatory" antibody isotype IgG4 was induced a few weeks after the third dose, which peaked abruptly and remained at high levels for a long period. Moreover, the high levels of IgG4 were concurrent with high neutralizing percentages against various VOCs including Omicron. (5) Subjects with IBD also produced IgG4 antibodies after the third dose, although these antibody levels had a limited effect on the neutralizing capacity. Knowing that the mRNA vaccines do not prevent infections, the Omicron subvariants have been shown to be less pathogenic, and IgG4 levels have been associated with immunotolerance and numerous negative effects, the recommendations for the successive administration of booster vaccinations to people should be revised.

Potent neutralization by monoclonal human IgM against SARS-CoV-2 is impaired by class switch

To investigate the class‐dependent properties of anti‐viral IgM antibodies, we use membrane antigen capture activated cell sorting to isolate spike‐protein‐specific B cells from donors recently infected with SARS‐CoV‐2, allowing production of recombinant antibodies. We isolate 20, spike‐protein‐specific antibodies of classes IgM, IgG, and IgA, none of which shows any antigen‐independent binding to human cells. Two antibodies of class IgM mediate virus neutralization at picomolar concentrations, but this potency is lost following artificial switch to IgG. Although, as expected, the IgG versions of the antibodies appear to have lower avidity than their IgM parents, this is not sufficient to explain the loss of potency.

UnAIDed Class Switching in Activated B-Cells Reveals Intrinsic Features of a Self-Cleaving IgH Locus

Activation-induced deaminase (AID) is the major actor of immunoglobulin (Ig) gene diversification in germinal center B-cells. From its first description, it was considered as mandatory for class switch recombination (CSR), and this discovery initiated a long quest for all of the AID-interacting factors controlling its activity. The mechanisms focusing AID-mediated DNA lesions to given target sequences remain incompletely understood with regards the detailed characterization of optimal substrates in which cytidine deamination will lead to double strand breaks (DSBs) and chromosomal cleavage. In an effort to reconsider whether such CSR breaks absolutely require AID, we herein provide evidence, based on deep-sequencing approaches, showing that this dogma is not absolute in both human and mouse B lymphocytes. In activated B-cells from either AID-deficient mice or human AID-deficient patients, we report an intrinsic ability of the IgH locus to undergo "on-target" cleavage and subsequent synapsis of broken regions in conditions able to yield low-level CSR. DNA breaks occur in such conditions within the same repetitive S regions usually targeted by AID, but their repair follows a specific pathway with increased usage of microhomology-mediated repair. These data further demonstrate the role of AID machinery as not initiating de novo chromosomal cleavage but rather catalyzing a process which spontaneously initiates at low levels in an appropriately conformed IgH locus.

Stepwise generation of AID knock-in and conditional knockout mice from a single gene-targeting event

Activation-induced cytidine deaminase (AID) encoded by the Aicda gene initiates class-switch recombination and somatic hypermutation of immunoglobulin genes. In addition to this function, AID is also implicated in the epigenetic regulation in pluripotent stem cells and in the oncogenesis of lymphoid and non-lymphoid origins. To examine AID's role in specific cell types, we developed mouse strains of conditional knockout (Aicda-FL) and knock-in with a red fluorescent protein gene (RFP) inserted into the Aicda locus (Aicda-RFP). These two strains were obtained from a single targeting event in embryonic stem cells by a three-loxP or tri-lox strategy. Partial and complete recombination among the three loxP sites in the Aicda-RFP locus gave rise to Aicda-FL and AID-deficient loci (Aicda-KO), respectively, after mating Aicda-RFP mice with Cre-expressing mice driven by tissue-non-specific alkaline phosphate promoter. We confirmed RFP expression in B cells of germinal centers of intestine-associated lymphoid tissue. Mice homozygous for each allele were obtained and were checked for AID activity by class-switch and hypermutation assays. AID activity was normal for Aicda-FL but partially and completely absent for Aicda-RFP and Aicda-KO, respectively. Aicda-FL and Aicda-RFP mice would be useful for studying AID function in subpopulations of B cells and in non-lymphoid cells.

Local increase in IgE and class switch recombination to IgE in nasal polyps in chronic rhinosinusitis

BACKGROUND

Chronic rhinosinusitis with nasal polyps is generally characterized by local Th2 inflammation and is categorized into two subtypes in Japan: eosinophilic chronic rhinosinusitis (similar to chronic rhinosinusitis with nasal polyps in western countries) and non-eosinophilic chronic rhinosinusitis (characterized by Th1-dominant inflammation).

OBJECTIVE

To investigate local IgE production and class switch recombination to IgE in these two subtypes of chronic rhinosinusitis with nasal polyps.

METHODS

The identity of IgE-positive cells was determined using double-immunofluorescent staining for IgE and cell-type-specific molecular markers. To investigate the local class switch recombination to IgE and IgE synthesis in the mucosa, we performed real-time polymerase chain reaction to examine the mRNA expression of Th2 cytokines and class-switch-related molecules, including IL-4, IL-5, IL-13, ε germline gene transcripts, IgE mature transcript, IgG mature transcript, RAG1, RAG2 and activation-induced cytidine deaminase in eosinophilic polyps, non-eosinophilic polyps and controls.

RESULTS

The concentrations of total IgE and number of IgE-positive cells were significantly higher in the eosinophilic polyps compared with control and non-eosinophilic polyps. IgE-positive cells were predominantly mast cells in eosinophilic polyps and significantly correlated with the number of FcεR1-positive cells in the subepithelial layer. IL-5 and IL-13 mRNA and ε germline gene transcripts expression levels were significantly higher in eosinophilic polyps compared with control and non-eosinophilic polyps. In contrast, the number of plasma cells and the expression of IgG mature transcripts were increased in non-eosinophilic polyps compared with eosinophilic polyps. RAG2 mRNA was significantly increased in both eosinophilic and non-eosinophilic polyps compared with control mucosa.

CONCLUSION AND CLINICAL RELEVANCE

The current study suggests local class switching to IgE, production of IgE and IgE localization to the surface of mast cells in eosinophilic chronic rhinosinusitis in the Japanese population. The difference in the IgE-related profiles between eosinophilic chronic rhinosinusitis and non-eosinophilic chronic rhinosinusitis suggests heterogeneity in the pathogenesis of chronic rhinosinusitis with nasal polyps.

Retinoic acid, acting as a highly specific IgA isotype switch factor, cooperates with TGF-β1 to enhance the overall IgA response

The present study demonstrates that RA has activity of an IgA switch factor and is more specific than TGF-β1. RA independently caused only IgA switching, whereas TGF-β1 caused IgA and IgG2b switching. We found that RA increased IgA production and that this was a result of its ability to increase the frequency of IgA-secreting B cell clones. Increased IgA production was accompanied by an increase of GLTα. RA activity was abrogated by an antagonist of the RAR. Additionally, RA affected intestinal IgA production in mice. Surprisingly, RA, in combination with TGF-β1, notably enhanced not only IgA production and GLTα expression but also CCR9 and α4β7 expression on B cells. These results suggest that RA selectively induces IgA isotype switching through RAR and that RA and TGF-β have important effects on the overall gut IgA antibody response.

Liposome-based polymer complex as a novel adjuvant: enhancement of specific antibody production and isotype switch

The aim of vaccination is to induce appropriate immunity against pathogens. Antibody-mediated immunity is critical for protection against many virus diseases, although it is becoming more evident that coordinated, multifunctional immune responses lead to the most effective defense. Specific antibody (Ab) isotypes are more efficient at protecting against pathogen invasion in different locations in the body. For example, compared to other Ab isotypes, immunoglobulin (Ig) A provides more protection at mucosal areas. In this study, we developed a cationic lipopolymer (liposome-polyethylene glycol-polyethyleneimine complex [LPPC]) adjuvant that strongly adsorbs antigens or immunomodulators onto its surface to enhance or switch immune responses. The results demonstrate that LPPC enhances uptake ability, surface marker expression, proinflammatory cytokine release, and antigen presentation in mouse phagocytes. In contrast to Freund’s adjuvant, LPPC preferentially activates Th1- immunity against antigens in vivo. With lipopolysaccharides or CpG oligodeoxynucleotides, LPPC dramatically enhances the IgA or IgG2A proportion of total Ig, even in hosts that have developed Th2 immunities and high IgG1 serum titers. Taken together, the results demonstrate that the LPPC adjuvant not only increases the immunogenicity of antigens but also modulates host immunity to produce an appropriate Ab isotype by combining with immunomodulators.

Evolution of antibody class switching: identification and transcriptional control of an Inu exon in the duck (Anas platyrhynchos)

Immunoglobulin class switching is characteristic to the tetrapod lineage, but the nature of this process has been elucidated only in mammals, where I-exon transcription initiates and directs the recombination in the IgH locus. Here, it is shown that an I-exon occurs 5' of the nu (IgY constant region) gene of the duck (Anas platyrhynchos): it is longer than mammalian I-exons and comprised primarily of tandem repeats. The Inu promoter was identified and shown to be responsive to stimulation with IL-4 but not LPS. It contains Oct, LYF-1, ATF, and C/EBP motifs. Site directed mutagenesis indicates that 2 C/EBP motifs are uniquely necessary for the response of the promoter to IL-4, as tested in the mouse pre-B cell line, 70Z/3. These results support the conclusion that the signal transduction pathways controlling I-exon promoter responses to cytokines have been highly conserved in vertebrate evolution.

Processing of switch transcripts is required for targeting of antibody class switch recombination

Antibody class switching is mediated by somatic recombination between switch regions of the immunoglobulin heavy chain gene locus. Targeting of recombination to particular switch regions is strictly regulated by cytokines through the induction of switch transcripts starting 5' of the repetitive switch regions. However, switch transcription as such is not sufficient to target switch recombination. This has been shown in mutant mice, in which the I-exon and its promoter upstream of the switch region were replaced with heterologous promoters. Here we show that, in the murine germline targeted replacement of the endogenous gamma1 promoter, I-exon, and I-exon splice donor site by heterologous promoter and splice donor sites directs switch recombination in activated B lymphocytes constitutively to the gamma1 switch region. In contrast, switch recombination to IgG1 is inhibited in mutant mice, in which the replacement does not include the heterologous splice donor site. Our data unequivocally demonstrate that targeting of switch recombination to IgG1 in vivo requires processing of the Igamma1 switch transcripts. Either the processing machinery or the processed transcripts are involved in class switch recombination.

A protein binding specifically to the IgG2b switch region

The Abelson-virus-transformed mouse pre-B-cell line 18-81 switches almost exclusively from mu to gamma 2b. From nuclear extracts of this cell line, we have isolated a factor that specifically binds to S gamma 2b. After an eight-step purification scheme, in which different types of DNA-affinity chromatography were used as key elements, we obtained a preparation with two narrowly spaced bands at approximately 69 kD on a silver-stained SDS gel. Binding specificity of main-peak fractions of affinity-purified proteins was analyzed by gel shift assays, in which S gamma 2b, but not S mu, competes. The results are consistent with this factor being part of the switch recombinase.

Circulating IgA, IgG, and IgM class antibody against Haemophilus parainfluenzae antigens in patients with IgA nephropathy

We previously demonstrated a close relationship between the outer membranes of Haemophilus parainfluenzae (HP) antigens (OMHP) and IgA nephropathy (IgAN). Our objective was to clarify the relationship among IgA, IgG, and IgM class antibody against OMHP in the sera of 44 patients with IgAN and 62 patients with other glomerular diseases (OGD) by ELISA. Patients with IgAN showed a significantly higher level of IgA antibodies (P less than 0.0005) and IgG antibodies (P less than 0.001) against OHMP, than did patients with OGD. Positive correlations were observed between IgA and IgG antibodies, between IgA and IgM antibodies, and between IgG and IgM antibodies against OMHP in the sera of patients with IgAN. Immunoblotting showed that IgA, IgG, or IgM antibodies against OMHP in the sera of all patients with IgAN bound to components of OMHP. Amino acid sequences of three components of OMHP recognized by the sera from patients with IgAN revealed homology with those reported for outer membrane protein (OMP) P6 precursor, OMP P5, and P2 porin protein of H. influenzae. Results suggest that patients with IgAN have glomerular deposits of OMP P6 precursor, OMP P5, or P2 porin protein of HP, and a specific increase in the production of IgA antibodies against OMHP via polyclonal activation against these, with switching of production from one isotype to another, e.g. from IgM to IgA.