Repertoire shift in the humoral response to phosphocholine-keyhole limpet hemocyanin: VH somatic mutation in germinal center B cells impairs T15 Ig function

Prognostic value of serum immunoglobulin M levels in patients with acute coronary syndrome

BACKGROUND AND AIMS

The immuno-inflammatory response is a crucial early step in the development of acute coronary syndrome (ACS). In this study, we investigated whether immunoglobulin M (IgM) in the body's initial immune response can predict the prognosis of patients with ACS.

METHODS

This prospective cohort study enrolled 1556 ACS patients at Beijing Hospital between March 2017 and October 2020. All patients underwent coronary angiography (CAG). The serum IgM concentration and biochemical indicators were evaluated prior to CAG. The primary endpoint was the composite endpoint of major adverse cardiovascular and cerebrovascular events (MACCEs). Multivariate Cox proportional hazards models was used to explore the association between IgM levels and the endpoint.

RESULTS

The average serum IgM levels of the population was 61.3 (42.6-88.4) mg/dL. During the median follow-up period of 55 months, 150 MACCEs occurred. Kaplan-Meier analysis showed that low serum IgM levels were associated with occurrence of MACCEs (log-rank p = 0.009). Univariate Cox proportional hazards models showed that low serum IgM (≤78.05 mg/dL) was associated with MACCEs (hazard ratio (HR) 1.648, 95 % confidence interval (CI): 1.129-2.406, p = 0.010). In patients with IgM ≤78.05 mg/dL, the HR for partially adjusted MACCEs events was 1.576 (95 % CI: 1.075-2.310) and 1.930 (95 % CI: 1.080-3.449) after adjusting for multiple covariates. The subgroup analysis showed that for patients in ≤24 BMI, never smoking and non-dyslipidemia subgroup, the lower serum IgM levels was significantly associated with the risk of MACCEs (pinteraction < 0.001, pinteraction = 0.037, pinteraction = 0.024, respectively).

CONCLUSIONS

Low serum IgM levels was independently associated with MACCEs in ACS patients, especially for patients without obesity, smoking and dyslipidemia.

Ancestral reconstruction reveals catalytic inactivation of activation-induced cytidine deaminase concomitant with cold water adaption in the Gadiformes bony fish

BACKGROUND

Antibody affinity maturation in vertebrates requires the enzyme activation-induced cytidine deaminase (AID) which initiates secondary antibody diversification by mutating the immunoglobulin loci. AID-driven antibody diversification is conserved across jawed vertebrates since bony and cartilaginous fish. Two exceptions have recently been reported, the Pipefish and Anglerfish, in which the AID-encoding aicda gene has been lost. Both cases are associated with unusual reproductive behavior, including male pregnancy and sexual parasitism. Several cold water fish in the Atlantic cod (Gadinae) family carry an aicda gene that encodes for a full-length enzyme but lack affinity-matured antibodies and rely on antibodies of broad antigenic specificity. Hence, we examined the functionality of their AID.

RESULTS

By combining genomics, transcriptomics, immune responsiveness, and functional enzymology of AID from 36 extant species, we demonstrate that AID of that Atlantic cod and related fish have extremely lethargic or no catalytic activity. Through ancestral reconstruction and functional enzymology of 71 AID enzymes, we show that this enzymatic inactivation likely took place relatively recently at the emergence of the true cod family (Gadidae) from their ancestral Gadiformes order. We show that this AID inactivation is not only concordant with the previously shown loss of key adaptive immune genes and expansion of innate and cell-based immune genes in the Gadiformes but is further reflected in the genomes of these fish in the form of loss of AID-favored sequence motifs in their immunoglobulin variable region genes.

CONCLUSIONS

Recent demonstrations of the loss of the aicda gene in two fish species challenge the paradigm that AID-driven secondary antibody diversification is absolutely conserved in jawed vertebrates. These species have unusual reproductive behaviors forming an evolutionary pressure for a certain loss of immunity to avoid tissue rejection. We report here an instance of catalytic inactivation and functional loss of AID rather than gene loss in a conventionally reproducing vertebrate. Our data suggest that an expanded innate immunity, in addition to lower pathogenic pressures in a cold environment relieved the pressure to maintain robust secondary antibody diversification. We suggest that in this unique scenario, the AID-mediated collateral genome-wide damage would form an evolutionary pressure to lose AID function.

NMR-based metabolic characterization of chicken tissues and biofluids: a model for avian research

INTRODUCTION

Poultry is one of the most consumed meat in the world and its related industry is always looking for ways to improve animal welfare and productivity. It is therefore essential to understand the metabolic response of the chicken to new feed formulas, various supplements, infections and treatments.

OBJECTIVES

As a basis for future research investigating the impact of diet and infections on chicken's metabolism, we established a high-resolution proton nuclear magnetic resonance (NMR)-based metabolic atlas of the healthy chicken (Gallus gallus).

METHODS

Metabolic extractions were performed prior to 1H-NMR and 2D NMR spectra acquisition on twelve biological matrices: liver, kidney, spleen, plasma, egg yolk and white, colon, caecum, faecal water, ileum, pectoral muscle and brain of 6 chickens. Metabolic profiles were then exhaustively characterized.

RESULTS

Nearly 80 metabolites were identified. A cross-comparison of these matrices was performed to determine metabolic variations between and within each section and highlighted that only eight core metabolites were systematically found in every matrice.

CONCLUSION

This work constitutes a database for future NMR-based metabolomic investigations in relation to avian production and health.

Atherosclerosis Susceptibility in Mice Is Independent of the V1 Immunoglobulin Heavy Chain Gene

Supplemental Digital Content is available in the text.

The V1 (V_HS107.1.42) immunoglobulin heavy chain gene is thought to be critical in producing IgM natural antibodies of the T15-idiotype that protect against both atherosclerosis and infection from Streptococcus pneumoniae. Our aim was to determine whether genetic loss of the V1 gene increased atherosclerotic plaque burden in vivo because of a reduction in the T15-idiotype or other atheroprotective antibodies.

An asymmetric antibody repertoire is shaped between plasmablasts and plasma cells after secondary immunization with (4-hydroxy-3-nitrophenyl)acetyl chicken γ-globulin

Studies on the structural basis of antibody affinity maturation have been carried out by measuring the affinity of secreted antibodies, and information on structures has often been obtained from nucleotide sequences of BCRs of memory B cells. We considered it important to establish whether the repertoire of secreted antibodies from plasma cells is really in accord with that of BCRs on memory B cells at the same time points post-immunization. We isolated plasma cells secreting antibodies specific to (4-hydroxy-3-nitrophenyl)acetyl (NP) hapten by affinity matrix technology using biotin-anti-CD138 and streptavidin-NP-allophycocyanin, to which anti-NP antibodies secreted by autologous plasma cells bound preferentially. We found that plasmablasts occupied >90% of the antibody-secreting cell compartment in the primary response and that they secreted antibodies whose VH regions were encoded by V186.2(+)Tyr95(+) sequences, which provided an increase in the medium level of affinity by somatic hypermutation (SHM) of heavy chains at position 33. After secondary immunization, a further increase in antibody affinity was observed, which was explained by the appearance of a number of plasma cells secreting V186.2(+)Gly95(+) antibodies that acquired high affinity by multiple SHMs as well as plasmablasts secreting V186.2(+)Tyr95(+) antibodies. However, we did not detect any plasmablasts secreting V186.2(+)Gly95(+) antibodies, showing that plasmablasts and plasma cells have a different antibody repertoire, i.e. their respective repertoires are asymmetric. On the basis of these findings, we discussed the relationship between the BCR affinity of memory B cells and plasmablasts as well as plasma cells as pertaining to their ontogeny.

The amino acid residue at position 95 and the third CDR region in the H chain determine the ceiling affinity and the maturation pathway of an anti-(4-hydroxy-3-nitrophenyl)acetyl antibody

Two groups of anti-(4-hydroxy-3-nitrophenyl)acetyl (NP) Abs each possessing a different amino acid, Tyr or Gly, at position 95, appeared respectively at early and late stages of immunization. The early Abs predominantly harbored Tyr95 and were referred to as the Tyr95 type. These had ∼100-fold lower ceiling affinity than the late Abs harboring Gly95, which were referred to as the Gly95 type. We found that in order to raise affinity, the Tyr95 type utilized a mutation at position 33 in V(H), while the Gly95 type used multiple mutations in both V(H) and V(L), and that the effect of the mutations was reciprocal; the former mutation had a positive effect on Tyr95 type Abs but a negative effect on Gly95 type Abs, and vice versa. The reciprocal effect of these mutations on affinity enabled us to assess the type of Abs prepared by introducing 20 different amino acids at position 95. We found that Abs harboring Lys95, Arg95, Pro95, and Tyr95 belonged to the Tyr95 type and those with Ala95 and Gly95, to the Gly95 type. Since this dependency on the amino acid at position 95 was observed in H chains whose third CDR (CDR 3H) consisted of 9 amino acids and not 11, the CDR 3H region was also considered to play an important role in determining the maturation pathway and the magnitude of the ceiling affinity.

Generation of B cell memory to the bacterial polysaccharide alpha-1,3 dextran

B1b B cells generate a novel form of memory and provide Ab mediated-protection to persisting bacterial pathogens. To understand how B1b B cells establish memory to polysaccharide Ags, we studied an oligoclonal B cell response to alpha-1,3 dextran (DEX) expressed on Enterobacter cloacae. B cells specific for DEX enrich in the marginal zone (MZ) and B1b B cell populations. After E. cloacae immunization, MZ B cells were responsible for the generation of initial peak DEX-specific Ab titers, whereas, DEX-specific B1b B cells expanded and played an important role in boosted production of DEX-specific Ab titers upon E. cloacae rechallenge. Cell transfer experiments demonstrate that B1b B cells possess the capacity for both robust proliferation and plasma cell differentiation, thus distinguishing themselves from MZ B cells, which uniformly commit to plasma cell differentiation. These results define B1b B cells as the principal reservoir for memory to bacterial-associated polysaccharide Ags.

Mouse monoclonal antibodies to pneumococcal C-polysaccharide backbone show restricted usage of VH-DH-JH gene segments and share the same kappa chain

The immunization of BALB/c mice with heat-killed cells of Streptococcus mitis SK598 allowed the rescue of mouse monoclonal antibodies (mAbs) reactive with the pneumococcal cell wall C-polysaccharide backbone. We report for the first time the genetic and molecular characterization of these mAbs, which altogether reflect a typical thymus-independent type 2 immune response. They were isotype-diverse (IgM, IgG1, IgG2b and IgG3). They made use of restricted and scarcely mutated VH-DH-JH combinations, and the same kappa chain, essentially in germ line configuration. Interestingly, this light chain was also found making up part of an anti-phosphorylcholine mAb. These mAbs were not inhibited by phosphorylcholine and related compounds, nor N-acetylneuraminic acid (NANA), nor the Forssman disaccharide; some of them showed limited reactivity with the meningococcal C polysaccharide. Their CDR-H3s do not show any recognizable patterns resembling those found in antibodies to bacterial polysaccharides that have already been characterized.

Sensitization with Xenogeneic Tissues Alters the Heavy Chain Repertoire of Human Anti-Galα1–3Gal Antibodies

BACKGROUND

Antigen sensitization alters the use of genes encoding the variable and constant regions of immunoglobulin, changing avidity, and function. Alterations in variable region genes induced by carbohydrate antigens have been studied extensively in animals but are incompletely characterized in humans. We asked how sensitization with the carbohydrate Galalpha1-3Gal modifies antibody heavy chain use.

METHODS

To overcome limited access to B cells, we analyzed anti-Galalpha1-3Gal antibodies from the serum of naïve and sensitized human subjects with anti-sera specific for VH families.

RESULTS

We find that in preimmune subjects, heavy chains of IgM anti-Galalpha1-3Gal derived primarily from VH3 family members, whereas the heavy chains of IgG are from diverse VH families. After sensitization, heavy chains of IgM and IgG antibodies both derived from diverse VH families.

CONCLUSIONS

The preimmune repertoire of IgM antibodies to Galalpha1-3Gal is thus more restricted than the antibody repertoire after sensitization, suggesting an antigen-induced shift in the repertoire.