IgG Subclass Concentrations in Certified Reference Material 470 and Reference Values for Children and Adults Determined with The Binding Site Reagents

IgG subclass levels in referred hemochromatosis probands with HFE p.C282Y/p.C282Y

BACKGROUND

IgG subclass levels in hemochromatosis are incompletely characterized.

METHODS

We characterized IgG subclass levels of referred hemochromatosis probands with HFE p.C282Y/p.C282Y (rs1800562) and human leukocyte antigen (HLA)-A and -B typing/haplotyping and compared them with IgG subclass levels of eight published cohorts of adults unselected for hemochromatosis.

RESULTS

There were 157 probands (82 men, 75 women; mean age 49±13 y). Median serum ferritin, mean body mass index (BMI), median IgG4, and median phlebotomy units to achieve iron depletion were significantly higher in men. Diabetes, cirrhosis, and HLA-A*03,-B*44, -A*03,B*07, and -A*01,B*08 prevalences and median absolute lymphocyte counts in men and women did not differ significantly. Mean IgG subclass levels [95% confidence interval] were: IgG1 5.31 g/L [3.04, 9.89]; IgG2 3.56 g/L [1.29, 5.75]; IgG3 0.61 g/L [0.17, 1.40]; and IgG4 0.26 g/L [<0.01, 1.25]. Relative IgG subclasses were 54.5%, 36.6%, 6.3%, and 2.7%, respectively. Median IgG4 was higher in men than women (0.34 g/L [0.01, 1.33] vs. 0.19 g/L [<0.01, 0.75], respectively; p = 0.0006). A correlation matrix with Bonferroni correction revealed the following positive correlations: IgG1 vs. IgG3 (p<0.01); IgG2 vs. IgG3 (p<0.05); and IgG2 vs. IgG4 (p<0.05). There was also a positive correlation of IgG4 vs. male sex (p<0.01). Mean IgG1 was lower and mean IgG2 was higher in probands than seven of eight published adult cohorts unselected for hemochromatosis diagnoses.

CONCLUSIONS

Mean IgG subclass levels of hemochromatosis probands were 5.31, 3.56, 0.61, and 0.26 g/L, respectively. Median IgG4 was higher in men than women. There were positive associations of IgG subclass levels. Mean IgG1 may be lower and mean IgG2 may be higher in hemochromatosis probands than adults unselected for hemochromatosis.

Clinical Performance of Immunonephelometric Assay and Chemiluminescent Immunoassay for Detection of IgG Subclasses in Chinese

BACKGROUND

Detection of IgG subclasses (IgGSc) is vital for the diagnosis and management of disease, especially IgG4-related diseases (IgG4-RD). This study aimed to evaluate the performances of the chemiluminescent immunoassay (CLIA) for detecting IgGSc and diagnosing IgG4-RD by IgGSc.

METHODS

A total of 40 individuals with IgG4-RD, 40 with primary Sjogren's syndrome (pSS), and 40 healthy controls (HCs) were enrolled. Serum samples were collected for the simultaneous detection of IgG1, IgG2, IgG3, and IgG4 by the Siemens immunonephelometric assay and the CLIA. The correlation analysis was performed, and diagnostic value was analyzed by the receiver operating characteristic (ROC) curve.

RESULTS

Patients with IgG4-RD had higher IgG4 (p < 0.001) and lower IgG1 (p < 0.001) than those with pSS, and HC. The results by the Siemens immunonephelometric assay and the CLIA showed a strong correlation in detecting IgG1, IgG2, IgG3, and IgG4 (r = 0.937, r = 0.847, r = 0.871, r = 0.990, all p < 0.001, respectively). The sum of IgG1, IgG2, IgG3, and IgG4 using two assays strongly correlated with total IgG by the IMMAGE 800 (r = 0.866, r = 0.811, both p < 0.001, respectively). For discriminating IgG4-RD from pSS and HC, no significant differences were observed in CLIA IgG4 and Siemens immunonephelometric assay IgG4 (z = 0.138, p = 0.891), which provided the area under the curves (AUCs) of 0.951 (p < 0.001) and 0.950 (p < 0.001), respectively. The AUCs of CLIA IgG1 and Siemens immunonephelometric assay IgG1 in distinguishing pSS from IgG4-RD and HC were 0.761 (p < 0.001) and 0.765 (p < 0.001), respectively, with no significant differences (z = 0.228, p = 0.820).

CONCLUSIONS

The CLIA and the Siemens immunonephelometric assay appeared to have good consistency with comparable diagnostic value in detecting IgGSc, especially IgG4, and IgG1 that can accurately identify IgG4-RD or pSS in clinical practice.

Disturbances in the IgG Antibody Profile in HIV-Exposed Uninfected Infants Associated with Maternal Factors

Over the last 20 years, the incidence of vertical HIV transmission has decreased from 25%-42% to less than 1%. Although there are no signs of infection, the health of HIV-exposed uninfected (HEU) infants is notoriously affected during the first months of life, with opportunistic infections being the most common disease. Some studies have reported effects on the vertical transfer of antibodies, but little is known about the subclass distribution of these antibodies. We proposed to evaluate the total IgG concentration and its subclasses in HIV+ mothers and HEU pairs and to determine which maternal factors condition their levels. In this study, plasma from 69 HEU newborns, their mothers, and 71 control pairs was quantified via immunoassays for each IgG isotype. Furthermore, we followed the antibody profile of HEUs throughout the first year of life. We showed that mothers present an antibody profile characterized by high concentrations of IgG1 and IgG3 but reduced IgG2, and HEU infants are born with an IgG subclass profile similar to that of their maternal pair. Interestingly, this passively transferred profile could remain influenced even during their own antibody production in HEU infants, depending on maternal conditions such as CD4+ T-cell counts and maternal antiretroviral treatment. Our findings indicate that HEU infants exhibit an altered IgG subclass profile influenced by maternal factors, potentially contributing to their increased susceptibility to infections.

High-Throughput Glycan Profiling of Human Serum IgG Subclasses Using Parallel Reaction Monitoring Peptide Bond Fragmentation of Glycopeptides and Microflow LC-MS

LC-MS-based N-glycosylation profiling in four human serum IgG subclasses (IgG1, IgG2, IgG3, and IgG4) often requires additional affinity-based enrichment of specific IgG subclasses, owing to the high amino acid sequence similarity of Fc glycopeptides among subclasses. Notably, for IgG4 and the major allotype of IgG3, the glycopeptide precursors share identical retention time and mass and therefore cannot be distinguished based on precursor or glycan fragmentation. Here, we developed a parallel reaction monitoring (PRM)-based method for quantifying Fc glycopeptides through combined transitions generated from both glycosidic and peptide bond fragmentation. The latter enables the subpopulation of IgG3 and IgG4 to be directly distinguished according to mass differences without requiring further enrichment of specific IgG subclasses. In addition, a multinozzle electrospray emitter coupled to a capillary flow liquid chromatograph was used to increase the robustness and detection sensitivity of the method for low-yield peptide backbone fragment ions. The gradient was optimized to decrease the overall run time and make the method compatible with high-throughput analysis. We demonstrated that this method can be used to effectively monitor the relative levels of 13 representative glycoforms, with a good limit of detection for individual IgG subclasses.

Development of an LC-MS/MS method for absolute quantification of IgG4 by evaluating dependence on the digestion efficiency using a non-cleavable/dually-cleavable internal calibrator set

The measurement of serum IgG4 levels is mandatory for the diagnosis of IgG4-related disease, but no widely accepted reference material exists due to a lack of consensus on the standard assay. Therefore, we developed here an LC-MS/MS method for absolute quantification of IgG4 in a purified IgG sample, addressing a concern over the reliability depending on the proteolytic digestion efficiency. Our method uses internal calibrator sets containing unique amino acid sequences within IgG4, each of which comprises non-cleavable and dually-cleavable peptides labeled with different numbers of isotopes for mass separation, to determine digestion efficiency. Surrogate peptides generated by trypsin or lysyl endopeptidase digestion were selected based on selectivity, stability, and identifiability. IgG4 quantification using synthetic calibrator peptides showed high precision across the two conditions with different peptidases (relative differences ≤6.1%), even with low digestion efficiencies (<20%), which was within the interday precision under an established condition (% coefficient of variation ≤6.9%, digestion efficiencies >90%, n = 5). These results indicate that the LC-MS/MS method for quantifying IgG4 is robust against digestion efficiency variations and is applicable to validating an IgG4 reference material.

A robust nanoscale RP HPLC-MS approach for sensitive Fc proteoform profiling of IgG allotypes

The conserved region (Fc) of IgG antibodies dictates the interactions with designated receptors thus defining the immunological effector functions of IgG. Amino acid sequence variations in the Fc, recognized as subclasses and allotypes, as well as post-translational modifications (PTMs) modulate these interactions. Yet, the high similarity of Fc sequences hinders allotype-specific PTM analysis by state-of-the-art bottom-up methods and current subunit approaches lack sensitivity and face co-elution of near-isobaric allotypes. To circumvent these shortcomings, we present a nanoscale reversed-phase (RP) HPLC-MS workflow of intact Fc subunits for comprehensive characterization of Fc proteoforms in an allotype- and subclass-specific manner. Polyclonal IgGs were purified from individuals followed by enzymatic digestion releasing single chain Fc subunits (Fc/2) that were directly subjected to analysis. Chromatographic conditions were optimized to separate Fc/2 subunits of near-isobaric allotypes and subclasses allowing allotype and proteoform identification and quantification across all four IgG subclasses. The workflow was complemented by a semi-automated data analysis pipeline based on the open-source software Skyline followed by post-processing in R. The approach revealed pronounced differences in Fc glycosylation between donors, besides inter-subclass and inter-allotype variability within donors. Notably, partial occupancy of the N-glycosylation site in the CH3 domain of IgG3 was observed that is generally neglected by established approaches. The described method was benchmarked across several hundred runs and showed good precision and robustness. This methodology represents a first mature Fc subunit profiling approach allowing truly subclass- and allotype-specific Fc proteoform characterization beyond established approaches. The comprehensive information obtained paired with the high sensitivity provided by the miniaturization of the approach guarantees applicability to a broad range of research questions including clinically relevant (auto)antibody characterization or pharmacokinetics assessment of therapeutic IgGs.

Observation of Heavy-Chain C-Terminal Des-GK Truncation in Recombinant and Human Endogenous IgG4

Therapeutic IgG mAbs have shown presence of three variations of their heavy chain C-termini, including the unprocessed C-terminal lysine, the processed C-terminal lysine, and C-terminal amidation. These variants are also present in endogenous human IgGs, although the level of unprocessed C-terminal lysine is very low. Here we report a new heavy-chain C-terminal variant, i.e., the des-GK truncation, which exists in both recombinant and endogenous human IgG4. The des-GK truncation was found in negligible amount in IgG1, IgG2 and IgG3 subclasses. Observation of a significant level of heavy-chain C-terminal des-GK truncation in endogenous human IgG4 suggests that low level of this variant present in therapeutic IgG4 is unlikely to be a safety concern.

Caprylate/chromatography process to produce highly purified tetanus immune globulin from human plasma

While tetanus toxoid vaccination has reduced the incidence of tetanus in the developed world, this disease remains a substantial health problem in developing nations. Tetanus immune globulin (TIG) is used along with vaccination for prevention of infection after major or contaminated wounds if vaccination status cannot be verified or for active tetanus infection. These studies describe the characterisation of a TIG produced by a caprylate/chromatography process. The TIG potency and presence of plasma protein impurities were analysed at early/late steps in the manufacturing process by chromatography, immunoassay, coagulation and potency tests. The caprylate/chromatography process has been previously shown to effectively eliminate or inactivate potentially transmissible agents from plasma-derived products. In this study, the caprylate/chromatography process was shown to effectively concentrate TIG activity and efficiently remove pro-coagulation factors, naturally present in plasma. This TIG drug product builds on the long-term evidence of the safety and efficacy of TIG by providing a product with higher purity and low pro-coagulant protein impurities.

The impact of IgG subclass deficiency on the risk of mortality in hospitalized patients with COPD

Background

Immunoglobulin G (IgG) deficiency increases the risk of acute exacerbations and mortality in chronic obstructive pulmonary disease (COPD). However, the impact of IgG subclass deficiency on mortality in COPD is unknown. Here, we determined which IgG subclass, if any, is associated with increased risk of mortality in COPD.

Methods

We measured serum IgG subclass concentrations of 489 hospitalized patients with COPD who were enrolled in the Rapid Transition Program (clinicaltrials.gov identifier NCT02050022). To evaluate the impact of IgG subclass deficiency on 1-year mortality, Cox proportional hazards regression analyses were performed with adjustments for potential confounders.

Results

Deficiencies in IgG1, IgG2, IgG3, and IgG4 were present in 1.8%, 12.1%, 4.3%, and 11.2% of patients, respectively. One-year mortality was 56% in patients with IgG1 deficiency, 27% in IgG2 deficiency, 24% in IgG3 deficiency, and 31% in IgG4 deficiency. Cox proportional modeling showed that IgG1 and IgG4 deficiencies increased the 1-year mortality risk with an adjusted hazard ratio of 3.92 (95% confidence interval [CI] = 1.55–9.87) and 1.74 (95% CI = 1.02–2.98), respectively. Neither IgG2 nor IgG3 deficiency significantly increased 1-year mortality. Two or more IgG subclass deficiencies were observed in 5.3%. Patients with 2 or more IgG subclass deficiencies had a higher 1-year mortality than those without any deficiencies (46.2% vs. 19.7%, p < 0.001), with an adjusted hazard ratio of 2.22 (95% CI = 1.18–4.17).

Conclusions

IgG1 and IgG4 deficiency was observed in 1.8% and 11.2% of hospitalized patients with COPD, respectively, and these deficiencies were associated with a significantly increased risk of 1-year mortality.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12931-022-02052-3.

Lung Function and Health Status in Individuals with Severe Alpha-1-Antitrypsin Deficiency at the Age of 42

Background

Severe hereditary alpha-1-antitrypsin deficiency (AATD) is a known risk factor for the early development of pulmonary emphysema and COPD, especially in smokers. By the Swedish national screening programme carried out from 1972 to 1974, a cohort of individuals with severe (PiZZ) AATD was identified and has been followed up regularly. The aim of this study was to investigate health status, quality of life and lung function in this cohort at the age of 42 years compared with an age-matched control group randomly selected from the population registry.

Methods

All study participants answered a questionnaire on smoking habits, symptoms, occupation, exposure to airway irritants and quality of life using Saint George’s Respiratory Questionnaire (SGRQ). They underwent complete pulmonary function tests (PFT) and forced oscillation technique (FOT) for the measurement of airway resistance and reactance. Blood samples were taken for allergies and IgG-subclasses as an indicator of increased risk of airway infections.

Results

The residual volume (RV), total lung capacity (TLC) and RV/TLC ratio were significantly higher in the PiZZ ever-smokers compared to the PiMM ever-smokers and PiZZ never-smokers (p < 0.05). The resistance in the upper, small and total airways was significantly lower in PiZZ subjects compared to PiMM subjects (p < 0.05). A greater proportion of PiZZ never-smokers had an FEV₁/VC ratio <0.7 than PiMM never-smokers (p = 0.043). PiZZ subjects with occupational exposure to airway irritants showed a significantly lower FEV₁, VC and higher RV/TLC ratio than PiMM individuals with exposure (p < 0.05).

Conclusion

At the age of 42, ever-smoking PiZZ individuals have signs of COPD, and also PiZZ never-smokers have early, physiological signs of emphysema.

Quantitation of IgG Subclasses in Serum Using Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS)

Serum IgG subclasses (IgGSC) are measured for a number of indications, but the most common are the identification of selective immunodeficiency disease and the diagnosis of IgG4-related disease (IgG4RD). Traditional nephelometric (IN) assays can suffer from two issues impacting the accuracy of the results: (1) hook effect and (2) antibody cross-reactivity between the subclasses. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) is not vulnerable to these modes of interference and therefore serves as an excellent and relatively inexpensive means of diagnosing and/or monitoring the relevant clinical conditions.We describe a semiautomated and simple method for the accurate and precise measurement of IgGSC from 20 μL of serum using a liquid chromatography and tandem mass spectrometry (LC-MS/MS) method following digestion of serum proteins in 96-well plate format. Due to the high abundance of the target proteins, no specialized sample preparation (such as solid phase extraction) is required. Twenty microliters are injected to the LC-MS/MS system. Quantitation is performed against a five-point duplicate linear calibration curve prepared in blank matrix. The assay calibration range is 0.38-7.74 g/L for IgG1, 0.24-4.46 g/L for IgG2, 0.038-0.752 g/L for IgG3, 0.025-0.435 g/L for IgG4, and 0.62-15.5 g/L for total IgG. Total IgG is used as an internal quality control marker and is compared to the sum of the four subclass results. Total imprecision in clinical production has been observed to be 5.1-10.6% for in-house prepared control materials having IgGSC mean values in the range of 0.38-8.43 g/L for IgG1, 0.22-3.76 g/L for IgG2, 0.0387-0.721 g/L for Ig3, and 0.0279-1.46 g/L for IgG4. Limit of quantitation (LoQ) was determined to be 0.29 g/L for IgG1, 0.22 g/L for IgG2, 0.019 g/L for IgG3, and 0.0067 g/L for IgG4.

A Critical Review on the Standardization and Quality Assessment of Nonfunctional Laboratory Tests Frequently Used to Identify Inborn Errors of Immunity

Inborn errors of immunity (IEI), which were previously termed primary immunodeficiency diseases, represent a large and growing heterogeneous group of diseases that are mostly monogenic. In addition to increased susceptibility to infections, other clinical phenotypes have recently been associated with IEI, such as autoimmune disorders, severe allergies, autoinflammatory disorders, benign lymphoproliferative diseases, and malignant manifestations. The IUIS 2019 classification comprises 430 distinct defects that, although rare individually, represent a group affecting a significant number of patients, with an overall prevalence of 1:1,200-2,000 in the general population. Early IEI diagnosis is critical for appropriate therapy and genetic counseling, however, this process is deeply dependent on accurate laboratory tests. Despite the striking importance of laboratory data for clinical immunologists, several IEI-relevant immunoassays still lack standardization, including standardized protocols, reference materials, and external quality assessment programs. Moreover, well-established reference values mostly remain to be determined, especially for early ages, when the most severe conditions manifest and diagnosis is critical for patient survival. In this article, we intend to approach the issue of standardization and quality control of the nonfunctional diagnostic tests used for IEI, focusing on those frequently utilized in clinical practice. Herein, we will focus on discussing the issues of nonfunctional immunoassays (flow cytometry, enzyme-linked immunosorbent assays, and turbidimetry/nephelometry, among others), as defined by the pure quantification of proteins or cell subsets without cell activation or cell culture-based methods.

Application of a caprylate/chromatography purification process for production of a high potency rabies immune globulin from pooled human plasma

BACKGROUND

Human rabies immunoglobulin (RIG) is an integral part of post-exposure prophylactic treatment of rabies (along with rabies vaccination). Infiltration of most, if not all, of the RIG dose at the wound site is recommended. RIG produced by a caprylate/chromatography manufacturing process (RIG-C; HyperRAB) increased the potency and purity of this product over the existing licensed RIG from a solvent/detergent process (RIG-S/D; HyperRAB-S/D).

METHODS

A series of studies were conducted to characterize the content and purity of RIG-C. A single-dose pharmacokinetic study in rabbits was performed to compare intramuscular (IM) immunoglobulin products manufactured by two different purification processes, solvent/detergent (IGIM-S/D) and caprylate/chromatography (IGIM-C).

RESULTS

RIG-C was found to be a highly purified IgG formulation with high monomer content and formulated with twice the anti-rabies potency of RIG-S/D while maintaining the same overall protein concentration. RIG-C facilitates IM administration at the wound site by halving the injection volume. The new caprylate/chromatography process eliminated detectible levels of pro-coagulant impurities and IgA that were carried through in the prior S/D process. These impurities have been associated with thrombotic complications and allergic reactions in susceptible patients. After single dose administration, IGIM-C was pharmacokinetically equivalent to IGIM-S/D in rabbits.

CONCLUSION

RIG-C is a more potent RIG formulation with less impurities yielding a safer and more convenient product with similar pharmacokinetic profile.

Factors associated with IgG levels in adults with IgG subclass deficiency

Background

Factors associated with IgG levels in adults with IgG subclass deficiency (IgGSD) are incompletely understood. We studied adults with IgGSD with subnormal IgG1 only, subnormal IgG1/IgG3, or subnormal IgG3 only without other subnormal IgG subclasses, IgA, or IgM. We compiled: age; sex; autoimmune condition(s) (AC); atopy; IgG, IgG subclasses, IgA, IgM; IgGsum (IgG1 + IgG2 + IgG3 + IgG4); and D (percentage difference between IgGsum and IgG). We compared attributes of patients with/without subnormal IgG (< 7.00 g/L; subnormal IgG1 subclass groups only) and analyzed IgGsum and IgG relationships. We performed backward stepwise regressions on IgG using independent variables IgG subclasses, age, and sex and on D using independent variables age and sex.

Results

There were 39 patients with subnormal IgG1 only (89.7% women), 53 with subnormal IgG1/IgG3 (88.7% women), and 115 with subnormal IgG3 only (91.3% women). Fifteen patients (38.5%) and 32 patients (60.4%) in the respective subnormal IgG1 subclass groups had subnormal IgG. Attributes of patients with/without IgG < 7.00 g/L were similar, except that AC prevalence was lower in patients with subnormal IgG1 only and IgG < 7.00 g/L than ≥ 7.00 g/L (p = 0.0484). Mean/median IgG1 and IgG2 were significantly lower in patients with IgG < 7.00 g/L in both subnormal IgG1 subclass groups (p < 0.0001, all comparisons). Regressions on IgG in three subclass groups revealed positive associations with IgG1 and IgG2 (p < 0.0001 each association). Regressions on D revealed no significant association. IgG1 percentages of IgGsum were lower and IgG2 percentages were higher in patients with subnormal IgG1 subclass levels than subnormal IgG3 only (p < 0.0001 all comparisons).

Conclusions

We conclude that both IgG1 and IgG2 are major determinants of IgG in patients with subnormal IgG1, combined subnormal IgG1/IgG3, or subnormal IgG3 and that in patients with subnormal IgG1 or combined subnormal IgG1/IgG3, median IgG2 levels are significantly lower in those with IgG < 7.00 g/L than those with IgG ≥ 7.00 g/L.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12865-021-00447-3.

Highly Sensitive Flow Cytometry Allows Monitoring of Changes in Circulating Immune Cells in Blood After Tdap Booster Vaccination

Antigen-specific serum immunoglobulin (Ag-specific Ig) levels are broadly used as correlates of protection. However, in several disease and vaccination models these fail to predict immunity. In these models, in-depth knowledge of cellular processes associated with protective versus poor responses may bring added value. We applied high-throughput multicolor flow cytometry to track over-time changes in circulating immune cells in 10 individuals following pertussis booster vaccination (Tdap, Boostrix®, GlaxoSmithKline). Next, we applied correlation network analysis to extensively investigate how changes in individual cell populations correlate with each other and with Ag-specific Ig levels. We further determined the most informative cell subsets and analysis time points for future studies. Expansion and maturation of total IgG1 plasma cells, which peaked at day 7 post-vaccination, was the most prominent cellular change. Although these cells preceded the increase in Ag-specific serum Ig levels, they did not correlate with the increase of Ig levels. In contrast, strong correlation was observed between Ag-specific IgGs and maximum expansion of total IgG1 and IgA1 memory B cells at days 7 to 28. Changes in circulating T cells were limited, implying the need for a more sensitive approach. Early changes in innate immune cells, i.e. expansion of neutrophils, and expansion and maturation of monocytes up to day 5, most likely reflected their responses to local damage and adjuvant. Here we show that simultaneous monitoring of multiple circulating immune subsets in blood by flow cytometry is feasible. B cells seem to be the best candidates for vaccine monitoring.

Time-related variation in IgG subclass concentrations in a group of healthy Danish adults

Introduction

Immunoglobulin G subclass measurements are important for the diagnostic work‐up of immunodeficiencies and immunoglobulin G4 (IgG4) related diseases. It is currently unknown whether a single sampling is truly representative for an individual's IgG subclass concentrations. This study aimed to investigate whether IgG and IgG subclass concentrations in healthy individuals are stable over time.

Method

With a span of median 42 weeks, four samples from each of 54 (34M, 20F) healthy adult volunteers (24–66 years) were analyzed for IgG and IgG1–4 using turbidimetry. Concentrations were compared within and between individuals.

Results

IgG and IgG subclass concentrations followed either a normal (IgG, IgG1, and IgG3) or log normal (IgG2 and IgG4) distribution. Immunoglobulin 4 demonstrated by far the widest range of concentrations between individuals (670‐fold: 0.004–2.68 g/L). Immunoglobulin G subclass variations within individuals were expressed as pooled standard deviations (PSD). These ranged from 0.056 (IgG4) to 0.955 g/L (IgG) and correlated with mean concentration of IgG or the particular IgG subclass. As a consequence, the relative PSDs (i.e., PSD divided by mean IgG or IgG subclass concentration) fell within a narrow range: 5.82%–10.1%. Based on these numbers, the 95%‐upper one‐sided confidence limits for intraindividual IgG and IgG subclass variation was calculated to range from 9.82% (IgG2) to 16.9% (IgG4).

Conclusion

The study documents that IgG or IgG subclass concentrations within healthy individuals are very stable over at least 42 weeks. The expected variation for IgG4 concentrations at a 95% confidence level does not exceed ±16.9%.

Low serum IgG4 level: a potential diagnostic biomarker for IgA nephropathy

Background

In contrast to intense investigations of galactose-deficient immunoglobulin A (IgA)1 specific immunoglobulin G (IgG), little is known about the IgG subclasses in IgA nephropathy (IgAN). Low IgG4 levels in IgAN were noticed in our preliminary experiment. We aimed to verify the low IgG4 levels and investigate the related immune mechanism in IgAN.

Methods

A total of 112 healthy controls (HC) and 112 newly diagnosed IgAN patients were enrolled in this study. Patients with idiopathic membranous nephropathy (IMN), minimal change disease (MCD), or lupus nephritis (LN) were selected as disease controls (DC) (n=122). Serum IgG4 and IgG levels were detected by enzyme-linked immunosorbent assay (ELISA). The IgG4⁺ B, T helper 1 (Th1), and Th2 cells were measured by flow cytometry. Receiver operating characteristic curves (ROC) were performed to evaluate the diagnostic value of IgG4.

Results

Both IgG4 levels and IgG4/IgG in IgAN were lower than HC and DC (all P<0.001). Severe IgAN displayed lower IgG4 levels than mild IgAN (P=0.039). Patients with higher risk of renal progression (>50%) demonstrated lower IgG4 levels than lower-risk (≤15%) patients (P=0.019). The cutoff value of IgG4 in differentiating IgAN from HC and DC was 0.26 mg/mL [sensitivity 98.2%, specificity 82.4%, area under the curve (AUC): 0.941, P<0.0001] and 0.17 mg/mL (sensitivity 90.2%, specificity 85.2%, AUC: 0.937, P<0.0001), respectively. IgG4/IgG displayed similar diagnostic and differential ability. The IgG4⁺ B/B cells (P<0.0001) and Th2/Th (P=0.042) of IgAN were lower than HC.

Conclusions

Serum IgG4 levels were low in IgAN. Lower IgG4 levels indicated more severe disease conditions and higher risk of renal progression. Low serum IgG4 seemed to be a potential diagnostic biomarker for IgAN. Decreased IgG4⁺ B cells and Th2 cells may contribute to the low IgG4 levels in IgAN.

Immunoglobulin deficiencies in treated patients suffering from rheumatoid arthritis

Immunoglobulins and antibodies to immunoglobulins (autoimmunoglobulins) have been identified to be implicated in the pathogenesis of rheumatoid arthritis (RA). Immunoglobulin deficiencies have been suggested to account for the increased risk of infections in RA patients. This study was carried out to determine the prevalence of immunoglobulin deficiencies in patients with RA and the identification of putative contributing factors. Immunoglobulin levels in blood samples of patients with rheumatoid arthritis were evaluated by an immunonephelometric assay. Demographic and disease related data (including age, sex, smoking habits, disease duration and activity, inflammatory markers) were assessed, and associations were identified by regression analysis. 539 patients were enrolled between 2011 and 2013. The most common immunoglobulin (Ig) deficiencies were those of IgM (24.5%) and IgG (19.9%). Most frequent deficiencies of subclasses were observed for IgG1 (42.3%), followed by IgG4 (10.4%), IgG2 (7.2%), and IgG3 (5.4%). Regression analyses revealed that deficiencies of IgM, IgG, IgG1, and IgG2 were more prevalent in older patients. In addition, smoking was associated with IgG2 deficiency, and IgA deficiency was associated with female sex. Occurrence of infections was significantly increased in patients with IgG, IgG2, and IgG4 deficiencies. RA patients displayed high rates of IgG and IgM deficiencies. In consequence, the assessment of immunoglobulin status should precede the application of immune modulating drugs to prevent a potential risk of infectious diseases. Prospective studies are needed to investigate the influence of immune modulating drugs on IgG and IgG subclass levels.

Cut-off values of serum IgG4 among three reagents, including a novel IgG4 reagent: a multicenter study

Elevated serum IgG4 is a useful marker of IgG4-related disease (IgG4-RD) activity. However, there is no uniformity in the cut-off values of IgG4 among the various reagents. The aim of this study was to compare the measured and cut-off values of IgG4 assessed using three different reagents. This study enrolled 466 IgG4-RD and non-IgG4-RD patients who required measurement of serum IgG4 levels to diagnose or treat IgG4-RD. Serum IgG4 was measured using three reagents: N-assay LA IgG4 Nittobo (Nittobo), BS-NIA IgG4 (TBS), and N Latex IgG4 (Siemens). The values obtained using the three reagents were compared, and cut-off values were calculated for each. Although there was good correlation among the results with the three reagents, the measured and cut-off values were all different. The Nittobo values were 1.4 times the TBS values and the TBS values were almost half those of the Siemens values. ROC curve analysis showed cut-off values for the Nittobo, TBS, and Siemens reagents of 1.42, 1.31, and 2.38 g/L, respectively. The measured and cut-off values of serum IgG4 vary depending on the reagents used for the assay, although there is good correlation among the values measured by the three reagents.

Characterization of adult patients with IgG subclass deficiency and subnormal IgG2

Background

Adults with IgG subclass deficiency (IgGSD) with subnormal IgG2 are inadequately characterized.

Methods

We retrospectively analyzed observations in unrelated adults with IgGSD evaluated in a single hematology clinic (1991–2019) and selected those with subnormal serum IgG2 (<117 mg/dL (<1.2 g/L)) without corticosteroid therapy to describe: age; prevalence of women; upper/lower respiratory infection; autoimmune condition(s); atopy; other allergy; frequent or severe respiratory tract infection in first-degree relatives; IgG, IgG subclasses, IgA, and IgM; blood lymphocyte subpopulations; human leukocyte antigen (HLA)-A and -B types and haplotypes; and 23-valent pneumococcal polysaccharide vaccination (PPSV23) responses. We determined the prevalence of subnormal IgG2 among unrelated adults with IgGSD without corticosteroid therapy and compared general characteristics of those with and without subnormal IgG2.

Results

There were 18 patients (94.4% women) with subnormal IgG2. Mean age was 52 ± 11 y. Upper/lower respiratory infection occurred in 94.4%/74.8%, respectively. Autoimmune condition(s), atopy, other allergy, and frequent or severe respiratory infection in first-degree relatives occurred in 44.4%, 44.4%, 61.1%, and 22.2%, respectively. Median IgG2 was 105 mg/dL (83, 116). Subnormal IgG, IgG1, IgG3, IgG4, IgA, and IgM was observed in 66.7%, 50.0%, 100.0%, 5.6%, 33.3%, and 0%, respectively. Lymphocyte subpopulations were normal in most patients. HLA frequencies were similar in patients and controls. Three of 4 patients had no protective S. pneumoniae serotype-specific IgG levels before or after PPSV23. These 18 patients represent 7.6% of 236 adults with IgGSD. Prevalence of subnormal IgG, subnormal IgG3, and subnormal IgA was significantly greater in 18 adults with subnormal IgG2 than 218 adults without subnormal IgG2. Prevalence of subnormal IgM was significantly lower in patients with subnormal IgG2.

Conclusions

Characteristics of adults with IgGSD with subnormal IgG2 include female predominance, other immunologic abnormalities, subnormal IgG3 and/or IgG1, lack of HLA-A and -B association, and suboptimal PPSV23 response.

Chromosome 6p SNP microhaplotypes and IgG3 levels in hemochromatosis probands with HFE p.C282Y homozygosity

Subnormal IgG1 or IgG3 levels occurred in 30% of hemochromatosis probands with HFE p.C282Y homozygosity and were concordant in HLA-identical siblings. We sought to identify factors associated with IgG subclasses in Alabama probands with p.C282Y homozygosity evaluated for 500 kb microhaplotypes AAT and GGG defined by SNPs in chromosome 6p genes PGBD1, ZNF193, and ZNF165. In regressions on IgG subclasses, we used: age; sex; GGG (dichotomous); iron removed to achieve depletion; CD8+ T-lymphocytes; and other IgG subclasses. Among 49 probands, AAT and GGG occurred in 95.9% and 16.3%, respectively. Thirteen probands (26.5%) had subnormal IgG1; 11 probands (22.4%) had subnormal IgG3. Mean IgG3 was higher in probands with than without GGG (75 mg/dL [95% confidence interval 63, 89] vs. 58 mg/dL [49, 71], respectively; p = 0.0321). Regression on IgG3 revealed: GGG positivity (p = 0.0106); and IgG1 (p = 0.0015). In a replication cohort of 22 Portugal probands with p.C282Y homozygosity, mean IgG3 was higher in probands with than without GGG (46 ± 16 vs. 31 ± 12 mg/dL, respectively; p = 0.0410). We conclude that mean IgG3 levels are higher in hemochromatosis probands with p.C282Y homozygosity with chromosome 6p microhaplotype GGG than in probands homozygous for microhaplotype AAT.

Immunological Role of IgG Subclasses

The loss of tolerance to self-antigens is the unequivocal "red line" of autoimmunity: both development of autoreactive T and B cells and production of polyclonal autoantibodies represent seminal keys to the pathogenesis of protean autoimmune diseases. Most of these autoantibodies are immunoglobulins G (IgG), functionally distinguished in four subclasses named IgG1, IgG2, IgG3, and IgG4, due to structural differences in the hinge and heavy chain constant regions. Different studies analyzed serum levels of IgG subclasses in the course of different disorders, showing that they might have a pathogenic role by regulating interactions among immunoglobulins, Fc-gamma receptors, and complement. To date, the mechanisms promoting different IgG subclasses distribution during the natural history of most autoimmune diseases remain somewhat unclear. Evidence from the medical literature shows that the serum IgG profile is peculiar for many autoimmune diseases, suggesting that different subclasses could be specific for the underlying driving autoantigens. A better knowledge of IgG subsets may probably help to elucidate their pathological task, but also to define their relevance for diagnostic purposes, patients' personalized management, and prognosis assessment.

Serum IgG Levels and Risk of COPD Hospitalization: A Pooled Meta-analysis

BACKGROUND

Hypogammaglobulinemia (serum IgG levels < 7.0 g/L) has been associated with increased risk of COPD exacerbations but has not yet been shown to predict hospitalizations.

RESEARCH QUESTION

To determine the relationship between hypogammaglobulinemia and the risk of hospitalization in patients with COPD.

STUDY DESIGN AND METHODS

Serum IgG levels were measured on baseline samples from four COPD cohorts (n = 2,259): Azithromycin for Prevention of AECOPD (MACRO, n = 976); Simvastatin in the Prevention of AECOPD (STATCOPE, n = 653), Long-Term Oxygen Treatment Trial (LOTT, n = 354), and COPD Activity: Serotonin Transporter, Cytokines and Depression (CASCADE, n = 276). IgG levels were determined by immunonephelometry (MACRO; STATCOPE) or mass spectrometry (LOTT; CASCADE). The effect of hypogammaglobulinemia on COPD hospitalization risk was evaluated using cumulative incidence functions for this outcome and deaths (competing risk). Fine-Gray models were performed to obtain adjusted subdistribution hazard ratios (SHR) related to IgG levels for each study and then combined using a meta-analysis. Rates of COPD hospitalizations per person-year were compared according to IgG status.

RESULTS

The overall frequency of hypogammaglobulinemia was 28.4%. Higher incidence estimates of COPD hospitalizations were observed among participants with low IgG levels compared with those with normal levels (Gray's test, P < .001); pooled SHR (meta-analysis) was 1.29 (95% CI, 1.06-1.56, P = .01). Among patients with prior COPD admissions (n = 757), the pooled SHR increased to 1.58 (95% CI, 1.20-2.07, P < .01). The risk of COPD admissions, however, was similar between IgG groups in patients with no prior hospitalizations: pooled SHR = 1.15 (95% CI, 0.86-1.52, P =.34). The hypogammaglobulinemia group also showed significantly higher rates of COPD hospitalizations per person-year: 0.48 ± 2.01 vs 0.29 ± 0.83, P < .001.

INTERPRETATION

Hypogammaglobulinemia is associated with a higher risk of COPD hospital admissions.

Dynamics of immunoglobulin G subclasses during the first two years of life in Malawian infants born to HIV-positive mothers

Background

Maternal antibodies are key components of the protective responses of infants who are unable to produce their own IgG until 6 months of life. There is evidence that HIV-exposed uninfected children (HEU) have IgG levels abnormalities, that can be partially responsible for the higher vulnerability to infections in the first 2 years of the life of this population.

This retrospective study aimed to characterize the dynamics in plasma levels of total IgG and their isotypes during the first 2 years of life in HEU infants exclusively breastfed through 6 months of age.

Methods

Total IgG, IgG1, IgG2, IgG3 and IgG4 isotypes, and IgM and IgA plasma concentrations were determined by nephelometric methods in 30 Malawian infants born to HIV-positive women at month 1, 6 and 24 of life.

Results

At 1-month infants had a median concentration of total IgG of 8.48 g/l, (IQR 7.57–9.15), with an overrepresentation of the IgG1 isotype (89.0% of total) and low levels of IgG2 (0.52 g/l, IQR, 0.46–0.65). Total IgG and IgG1 concentrations were lower at 6 months (− 2.1 and − 1.12 g/dl, respectively) reflecting disappearance of maternal antibodies, but at 24 months their levels were higher with respect to the reported reference values for age-matched pairs. Abnormal isotype distribution was still present at 24 months with IgG2 remaining strongly underrepresented (0.87 g/l, 7.5% of total IgG).

Conclusion

HIV exposure during pregnancy and breastfeeding seems to influence the IgG maturation and isotype distribution that persist in 2-year old infants.

Immune globulin subcutaneous, human 20% solution (Xembify®), a new high concentration immunoglobulin product for subcutaneous administration

Immune globulin subcutaneous, human 20% solution (IGSC-C 20%, Xembify®)-a new 20% immunoglobulin (IgG) liquid product for subcutaneous (SC) administration-has been developed by Grifols. The IGSC-C 20% formulation is based on knowledge acquired from the formulation of Immune Globulin Injection (Human),10% Caprylate/Chromatography Purified (IGIV-C 10%, Gamunex®-C). The protein concentration was increased from 10% to 20% to provide a smaller volume for SC administration. The IGSC-C 20% manufacturing process employs the same caprylate/chromatography purification steps as IGIV-C 10%, with the addition of an ultrafiltration step so that the product can be formulated at a higher protein concentration. IGSC-C 20% has been produced at full industrial scale to support clinical studies and licensure. These batches were characterized using a comprehensive panel of analytical testing. The new IGSC-C 20% product maintains the same composition, neutralizing activity, purity, and quality characteristics found in IGIV-C 10%.

Basic Research and Clinical Reports Associated with Low Serum IgG4 Concentrations

Elevated IgG4 concentrations in serum have received a great deal of attention recently, whereas the significance of decreased IgG4 levels was frequently neglected in spite of its close relation with infectious and noninfectious inflammations. In this review, based on the structural and functional characteristics of IgG4, we bring together case reports and research related to low levels of IgG4 and try to scratch the importance of decreased IgG4 concentrations in serum. As with elevated IgG4 levels, low serum IgG4-related diseases can be involved in multiple systems such as infection in the respiratory system, stroke in the circulatory system, and glomerulonephritis in the urinary system. Both genetic and immune dysregulation can contribute to decreased IgG4 levels. In the light of animal experiments, we believe that the mystery of low IgG4 can be revealed as long as enough attention is acquired.

Evaluation of a novel serum IgG4 assay and determination of reference interval for the Japanese population

BACKGROUND

IgG4-related disease (IgG4-RD) is a new syndrome characterized by elevated serum IgG4 concentration and tissue infiltration of IgG4-positive plasma cells. Here, we evaluated the analytical performance of a new IgG4 assay reagent featuring a wide dynamic range, highly specific monoclonal antibody, and the reversed passive latex agglutination assay and determined the IgG4 reference interval (RI) for the Japanese population.

METHODS

Performance evaluations were conducted on precision, linearity, sensitivity, interference, and method comparison with The Binding Site (TBS) and Siemens reagents. The RI was derived by the parametric method from 619 apparently healthy Japanese 18 to 65 years of age.

RESULTS

Between-day precisions ranged from 1.99 to 5.52 CV%. Linearity was confirmed up to 5.0 g/l. The limit of quantitation was 0.085 g/l. Interfering substances did not significantly influence values. Method comparison among the 3 reagents yielded correlation coefficients between 0.973 and 0.988. Values for the new reagent matched those of TBS reagent except at a higher concentration range, where reactivity dissociated. The RI was 0.11-1.21 g/l without distinction by sex and age.

CONCLUSION

The novel IgG4 assay reagent demonstrated satisfactory analytical performance for clinical use. Because of matched value with TBS reagent at low concentrations, it is possible to use the IgG4-RD cut-off value determined by TBS reagent.

Variable and inaccurate serum IgG4 levels resulting from lack of standardization in IgG subclass assay calibration

Background

The quantification of serum IgG4 is commonly performed during the diagnostic workup of IgG4-related diseases (IgG4-RD). According to recent literature, IgG4 values above 1.35 g/L are characteristic of IgG4-RD and support its diagnosis at initial presentation. The purpose of this study was to evaluate comparability and accuracy of the two main commercially available IgG4 assays (Siemens Healthineers and The Binding Site).

Methods

Method comparison was performed for IgG and IgG subclasses using a collective of selected samples with elevated serum IgG4. In addition, we assessed the accuracy of both assays using purified polyclonal and monoclonal IgG4 preparations.

Results

Our data show significant discrepancies between the two IgG subclass assays for the measurement of IgG4 and, to a lesser extent, IgG3.

Conclusions

The lack of standardization between the two main providers of commercially available IgG4 assays leads to significant inter-assay result discrepancies, which might potentially cause unnecessary clinical workup. We conclude that serum IgG4 assay-specific decision limits, and not an assay-independent single cut-off level for IgG4 (e.g. 1.35 g/L), should be used when assessing patients for IgG4-RD. An internationally recognized, certified reference material for IgG subclasses is urgently needed, and assay manufactures are encouraged to undertake steps toward standardization of measurements of IgG4 and other IgG subclasses.

Clinical and laboratory associations of mannose-binding lectin in 219 adults with IgG subclass deficiency

Background

Mannose-binding lectin (MBL) deficiency may increase risk of respiratory tract infection in adults unselected for IgG or IgG subclass levels. In a retrospective study, we sought to determine associations of serum MBL levels with clinical and laboratory characteristics of unrelated non-Hispanic white adults at diagnosis of IgG subclass deficiency (IgGSD). We computed the correlation of first and second MBL levels expressed as natural logarithms (ln) in a patient subgroup. We compared these characteristics of all adults with and without MBL ≤50 ng/mL: age; sex; body mass index; upper/lower respiratory tract infection; diabetes; autoimmune condition(s); atopy; other allergy; corticosteroid therapy; and subnormal serum IgG subclasses, IgA, and IgM. We performed logistic regression on MBL ≤50 ng/mL (dichotomous) using the three independent variables with the lowest values of p in univariate comparisons.

Results

There were 219 patients (mean age 51 ± 13 y; 82.5% women). Thirty-six patients (16.4%) had MBL ≤50 ng/mL. Two MBL measurements were available in 14 patients. The median interval between the first and second measurements was 125 d (range 18–1031). For ln-transformed data, we observed adjusted r² = 0.9675; Pearson correlation coefficient 0.9849; and p < 0.0001. Characteristics of patients with and without MBL ≤50 ng/mL did not differ significantly in univariate comparisons. We performed a regression on MBL ≤50 ng/mL using: subnormal IgM (p = 0.0565); upper respiratory tract infection (p = 0.1094); and body mass index (p = 0.1865). This regression revealed no significant associations. Conclusions: We conclude that the proportion of the present IgGSD patients with serum MBL ≤50 ng/mL is similar to that of healthy European adults. MBL ≤50 ng/mL was not significantly associated with independent variables we studied.

Duration of frequent or severe respiratory tract infection in adults before diagnosis of IgG subclass deficiency

Many adults with IgG subclass deficiency (IgGSD) experience long intervals of frequent/severe respiratory tract infection before IgGSD diagnosis, but reasons for delays in IgGSD diagnoses are incompletely understood. We performed a retrospective study of 300 white adults (ages ≥18 y) with IgGSD including frequency analyses of age at IgGSD diagnosis, duration of frequent/severe respiratory tract infection before IgGSD diagnosis, and age at onset of frequent/severe infection (calculated). We performed multivariable regressions on age at diagnosis, infection duration, and age at infection onset using these variables, as appropriate: sex; age at diagnosis; diabetes; autoimmune condition(s); atopy; allergy; corticosteroid use; body mass index; serum immunoglobulin isotype levels; blood lymphocyte subsets; three IgGSD-associated human leukocyte antigen-A and -B haplotypes; and referring physician specialties. Mean age at diagnosis was 50 ± 12 (standard deviation) y (median 50 y (range 19–79)). There were 247 women (82.3%). Mean infection duration at IgGSD diagnosis was 12 ± 13 y (median 7 y (range 1–66)). Mean age at infection onset was 38 ± 16 y (median 38 y (range 4, 76)). Age at infection onset was ≥18 y in 95.7% of subjects. Regressions on age at diagnosis and infection duration revealed no significant associations. Regression on age at infection onset revealed one positive association: age at diagnosis (p <0.0001). We conclude that the median duration of frequent/severe respiratory tract infection in adults before IgGSD diagnosis was 7 y. Older adults may be diagnosed to have IgGSD after longer intervals of infection than younger adults. Duration of frequent/severe respiratory tract infection before IgGSD diagnosis was not significantly associated with routine clinical and laboratory variables, including referring physician specialties.

Reference ranges for serum immunoglobulin (IgG, IgA, and IgM) and IgG subclass levels in healthy children

Background/aim

The serum immunoglobulin levels are used routinely in clinical practice because they provide key information on the humoral immune status. This study aimed to determine the age-related reference values of serum immunoglobulin levels in healthy children.

Materials and methods

A total of 330 healthy children, aged between 0 and 18 years, were included in this study. The serum immunoglobulin levels were measured using a nephelometric method in a total of 11 groups, each group consisting of 30 individuals, and IgG subclasses in 6 groups of children aged more than 2 years.

Results

The serum IgG levels were high during the newborn period, decreased until the sixth month, and again increased to a maximum level at the age of 18 years. The level of IgA was found to be extremely low in the newborn period and then increased with age. While the lowest value was in the newborn period for serum IgM level, the highest value was in the 16- to 18-year-old period. The IgG subclasses varied depending on the age groups.

Conclusion

The updated reference intervals of immunoglobulin levels in children may be used for the accurate diagnosis of immune deficiencies.

Comparison of reference systems in the assessment of age-related serum immunoglobulin levels in pediatric patients

Background/aim

Ig level assessment is frequently used in the diagnosis and follow-up of immunodeficiency, as well as in studies investigating the prevalence of low serum Ig level in specific diseases.Material and methods: Patients who underwent Ig testing in the inpatient and outpatient clinics of our hospital in the years 2010–2016 were included. The Ig levels of the patients were assessed separately according to two reference systems commonly used in Turkey and another reference system used in the USA.

Results

A total of 20,138 patients (57.6% male) were included in the study. The median age of the patients was 55.7 months (interquartile range: 23.1–96.7). According to the reference intervals determined by Tezcan et al., 30.6% of the patients were deficient in one or more Ig values. This rate was 4 times higher than those based on the reference intervals determined by Aksu et al. (7.7%) and those in the Nelson Textbook of Pediatrics (6.8%). We also determined that the frequency of low Ig levels with three reference systems.Conclusion: In this study, we found that the rates of low Ig level in a group of pediatric patients differed significantly when evaluated using three different reference systems for age-related serum Ig levels

Contemporary analysis of functional immune recovery to opportunistic and vaccine-preventable infections after allogeneic haemopoietic stem cell transplantation

Objectives

Infections are a major cause of mortality after allogeneic haemopoietic stem cell transplantation (alloHSCT), and immune recovery is necessary for prevention. Novel transplant procedures have changed the epidemiology of infections but contemporary data on functional immune recovery are limited. In this pilot study, we aimed to measure immune recovery in the current era of alloHSCT.

Methods

Twenty, 13, 11, 9 and 9 alloHSCT recipients had blood collected at baseline (time of conditioning) and 3‐, 6‐, 9‐, and 12‐months post‐alloHSCT, respectively. Clinical data were collected, and immune recovery was measured using immunophenotyping, lymphocyte proliferation, cytokine analysis and antibody isotyping.

Results

Median absolute T‐ and B‐cell counts were below normal from baseline until 9‐ to 12‐months post‐alloHSCT. Median absolute CD4⁺ T‐cell counts recovered at 12‐months post‐alloHSCT. Positive proliferative responses to Aspergillus, cytomegalovirus (CMV), Epstein‐Barr virus (EBV), influenza and tetanus antigens were detected from 9 months. IL‐6 was the most abundant cytokine in cell cultures. In cultures stimulated with CMV, EBV, influenza and tetanus peptides, the CD4⁺ T‐cell count correlated with IL‐1β (P = 0.045) and CD8⁺ T‐cell count with IFNγ (P = 0.013) and IL‐1β (P = 0.012). The NK‐cell count correlated with IL‐1β (P = 0.02) and IL‐17a (P = 0.03). Median serum levels of IgG1, IgG2 and IgG3 were normal while IgG4 and IgA were below normal range throughout follow‐up.

Conclusions

This pilot study demonstrates that immune recovery can be measured using CD4⁺ T‐cell counts, in vitro antigen stimulation and selected cytokines (IFNγ, IL‐1β, IL‐4, IL‐6, IL‐17, IL‐21, IL‐31) in alloHSCT recipients. While larger studies are required, monitoring immune recovery may have utility in predicting infection risk post‐alloHSCT.

Immunoglobulin G (IgG) and IgG subclass reference intervals in children, using Optilite® reagents

Background:

Immunoglobulin G (IgG) and IgG subclass assays are indicated in patients with suspected primary immunodeficiency (PID). Commercially available assays for IgG subclass determination are calibrated against various preparations, and so specific reference values are required for each of them. Using Optilite® reagents from The Binding Site Group Ltd., we sought to determine the pediatric IgG and IgG subclass reference intervals with respect to the ERM-DA470k certified reference material.

Methods:

Levels of IgG and IgG subclasses were analyzed in serum samples collected from a large cohort of PID-free children and adolescents. Reference intervals were calculated for previously published age groups (6–12 months, 12–18 months, 18 months–2 years, 2–3 years, 3–4 years, 4–6 years, 6–9 years, 9–12 years and 12–18 years), according to the Clinical and Laboratory Standards Institute’s C28-A3c protocol.

Results:

A total of 456 serum samples were analyzed. The correlation between the total IgG and the sum of the IgG subclasses was good (r2=0.96). No statistically significant gender-specific differences were observed. Our results for the changes over time in IgG and IgG subclass levels are consistent with previous reports. The differences between our lower/upper reference limits and those in the literature are probably due to variations in calibration.

Conclusions:

Our present results provide a reliable basis for the diagnosis of PIDs in childhood and for the accreditation of laboratories using Optilite® immunoturbidimetric reagents for IgG subclass measurement. Laboratory scientists and clinicians should be aware of the need for manufacturer-specific IgG subclass reference intervals.

No Overt Clinical Immunodeficiency Despite Immune Biological Abnormalities in Patients With Constitutional Mismatch Repair Deficiency

Immunoglobulin class-switch recombination (CSR) and somatic hypermutations (SHMs) are prerequisites for antibody and immunoglobulin receptor maturation and adaptive immune diversity. The mismatch repair (MMR) machinery, consisting of homologs of MutSα, MutLα, and MutSβ (MSH2/MSH6, MLH1/PMS2, and MSH2/MSH3, respectively) and other proteins, is involved in CSR, primarily acting as a backup for nonhomologous end-joining repair of activation-induced cytidine deaminase-induced DNA mismatches and, furthermore, in addition to error-prone polymerases, in the repair of SHM-induced DNA breaks. A varying degree of antibody formation defect, from IgA or selective IgG subclass deficiency to common variable immunodeficiency and hyper-IgM syndrome, has been detected in a small number of patients with constitutional mismatch repair deficiency (CMMRD) due to biallelic loss-of-function mutations in one of the MMR genes (PMS2, MSH6, MLH1, or MSH2). To elucidate the clinical relevance of a presumed primary immunodeficiency (PID) in CMMRD, we systematically collected clinical history and laboratory data of a cohort of 15 consecutive, unrelated patients (10 not previously reported) with homozygous/compound heterozygous mutations in PMS2 (n = 8), MSH6 (n = 5), and MLH1 (n = 2), most of whom manifested with typical malignancies during childhood. Detailed descriptions of their genotypes, phenotypes, and family histories are provided. Importantly, none of the patients showed any clinical warning signs of PID (infections, immune dysregulation, inflammation, failure to thrive, etc.). Furthermore, we could not detect uniform or specific patterns of laboratory abnormalities. The concentration of IgM was increased in 3 out of 12, reduced in 3 out of 12, and normal in 6 out of 12 patients, while concentrations of IgG and IgG subclasses, except IgG4, and of IgA, and specific antibody formation were normal in most. Class-switched B memory cells were reduced in 5 out of 12 patients, and in 9 out of 12 also the CD38^hiIgM⁻ plasmablasts were reduced. Furthermore, results of next generation sequencing-based analyses of antigen-selected B-cell receptor rearrangements showed a significantly reduced frequency of SHM and an increased number of rearranged immunoglobulin heavy chain (IGH) transcripts that use IGHG3, IGHG1, and IGHA1 subclasses. T cell subsets and receptor repertoires were unaffected. Together, neither clinical nor routine immunological laboratory parameters were consistently suggestive of PID in these CMMRD patients, but previously shown abnormalities in SHM and rearranged heavy chain transcripts were confirmed.

Analysis of differences between total IgG and sum of the IgG subclasses in children with suspected immunodeficiency - indication of determinants

Background

Deficits in disorders of humoral immunity associated with a deficit of antibodies are the most common primary immunodeficiency. Total IgG and IgG subclasses measurements are used to diagnose, differentiate and control in patients with primary and secondary immunodeficiencies.

Methods

The purpose of the study was to analyze the structure patients group according to difference between total IgG and sum of the IgG subclasses and to determine factors affecting the level of this difference. This study was based on data collected from 670 children referred to the Department of Clinical Immunology and Pediatrics in order to diagnose the immune disorders. For all children the level of the total of immunoglobulins IgG and of the IgG subclasses (IgG1, IgG2, IgG3, IgG4) were determined. The group of children was divided into subgroups according to gender, age (under 6 years of age, 6.5–12 years, and 12–18 years), and IgG abnormality (below the normal range, normal and above the normal range). In the patients group, the total IgG values were on average higher than sum of the IgG subclasses.

Results

Statistical analysis shown the all parameters under study (age, gender and IgG abnormality) influence statistically significant on the discrepancy between the sum of the IgG subclasses and total IgG. Assessment of IgG and IgG subclasses levels is based on different methods what causes the discrepancy between the sum of the IgG subclasses and total IgG.

Conclusions

Standardization in that regard is crucial. In addition, we have shown the reliability of the results obtained. Despite the determination in two different laboratories and on different analyzers, as well as the freezing process does not affect the test results.

IgG response against Staphylococcus aureus is associated with severe atopic dermatitis in children

BACKGROUND

An altered immune response against Staphylococcus aureus might contribute to inflammation and barrier damage in atopic dermatitis (AD).

OBJECTIVES

To profile IgG antibodies against 55 S. aureus antigens in sera of children with mild-to-severe AD and to evaluate the association between IgG levels and disease severity.

METHODS

In this cross-sectional study, we included children with AD from two interventional study cohorts, the Shared Medical Appointment (SMA) cohort (n = 131) and the older DAVOS cohort (n = 76). AD severity was assessed using the Self-Administered Eczema Area and Severity Index (SA-EASI) and levels of thymus and activation-regulated chemokine (TARC) in serum. IgG antibody levels against 55 S. aureus antigens were quantified simultaneously using a Luminex assay. Pair-wise correlations were calculated between the 55 IgG levels using the Spearman rank correlation test. Linear regression analysis was performed to test for associations between 55 IgG levels and SA-EASI and TARC, adjusting for age, sex and S. aureus colonization.

RESULTS

In the SMA cohort, 16 antigens were associated with SA-EASI and 12 with TARC (10 overlapping antigens; P-values 0·001-0·044). The associated IgG antibodies targeted mainly secreted proteins with immunomodulatory functions. In the DAVOS study, IgG levels against only four and one S. aureus antigen(s) were associated with SA-EASI and TARC, respectively (no overlap).

CONCLUSIONS

In young children, severity of AD is associated with an IgG response directed against S. aureus antigens with mainly immunomodulatory functions. These findings encourage further evaluation of the role of S. aureus in the pathogenesis of AD.

The Clinical Utility of Measuring IgG Subclass Immunoglobulins During Immunological Investigation for Suspected Primary Antibody Deficiencies

Measurement of IgG subclass concentrations is a standard laboratory test run as part of a panel to investigate the suspicion of antibody deficiency. The assessment is clinically important when total IgG is within the normal age-specific reference range. The measurement is useful for diagnosis of IgG subclass deficiency, to aid the diagnosis of specific antibody deficiency, as a supporting test for the diagnosis of common variable immunodeficiency, as well as for risk stratification of patients with low IgA. The measurement of IgG subclasses may also help determine a revaccination strategy for patients and support patient management. In certain circumstances, the measurement of IgG subclasses may be used to monitor a patient’s humoral immune system. In this review, we discuss the utility of measuring IgG subclass concentrations.

Age-specific pediatric reference ranges for immunoglobulins and complement proteins on the Optilite™ automated turbidimetric analyzer

BACKGROUND

Measurement of immunoglobulins and complement proteins are frontline tests used in the assessment of immune system integrity, and reference values can vary with age. Their measurement provides an insight into the function of the innate and adaptive immune systems.

METHODS

We generated pediatric reference ranges for IgG, IgA, IgM, IgD, the IgG and IgA subclasses, and C3 and C4 using the Optilite™ turbidimetric analyzer.

RESULTS

The concentrations of IgG, IgA, and IgD showed an increase with age, as expected, while IgM remained stable between the age groups. For the IgG subclasses, no significant differences were observed in IgG1 or IgG3, while IgG2 and IgG4 concentrations increased steadily with age. The concentration of IgG2 plateaued at 15-18 years, while IgG4 plateaued at 10-14 years. The trend of concentrations across all groups was IgG1 > IgG2 > IgG3 > IgG4. For both IgA1 and IgA2, concentrations increased significantly with age, plateauing at 15-18 years. The median IgA1 concentration was greater than IgA2 across all groups. There was a good correlation between the total IgG or IgA concentration and summation of their subclasses (R²  = 0.89, P < .0001, slope y = 0.98x + 14.51 mg/dL and R²  = 0.91, P < .0001, slope y = 1.35x-3.28 mg/dL, respectively). The concentration of C3 and C4 remained stable across the groups, with no significant differences observed.

CONCLUSION

We have generated age-specific reference ranges in healthy children for C3, C4, IgG, IgA, IgM, IgD and the IgG and IgA subclasses using the Optilite^™ turbidimetric analyzer. These ranges will help identify individuals with abnormal concentrations, thus will aid in the diagnosis of both primary and secondary immunological disorders.

A reference interval for serum IgG subclasses in Chinese children

Background

Reference intervals (RIs) for serum IgG subclasses vary greatly among different geographical regions. The present study aimed to establish RIs for serum IgG subclasses in Chinese children, which is essential for interpretation of laboratory findings and making clinical decisions.

Methods

This study was performed in accordance with guideline C28-A3, proposed by the International Federation of Clinical Chemistry and the Clinical and Laboratory Standards Institute. In total, 607 apparently healthy Chinese children were enrolled, and serum levels of IgG subclasses were measured. Individuals were stratified by age and the RIs were determined through statistical analysis.

Results

Following were the median values of RIs for serum IgG subclasses in Chinese children: IgG1, 2.78 g/L; IgG2, 0.85 g/L; IgG3, 0.13 g/L; IgG4, 0.06 g/L at 1–6 months of age; IgG1, 3.64 g/L; IgG2, 0.73 g/L; IgG3, 0.19 g/L; IgG4, 0.03 g/L at 6–12 months of age; IgG1, 5.15 g/L; IgG2, 0.87 g/L; IgG3, 0.19 g/L; IgG4, 0.07 g/L at 1–2 years of age; IgG1, 5.26 g/L; IgG2, 1.23 g/L; IgG3, 0.14 g/L; IgG4, 0.11 g/L at 2–3 years of age; IgG1, 6.33 g/L; IgG2, 1.8 g/L; IgG3, 0.2 g/L; IgG4, 0.21 g/L at age 3–4 years; IgG1, 7.05 g/L; IgG2, 1.87 g/L; IgG3, 0.25 g/L; IgG4, 0.29 g/L at 4–6 years of age; IgG1, 6.19 g/L; IgG2, 1.93 g/L; IgG3, 0.2 g/L; IgG4, 0.28 g/L at 6–9 years of age; IgG1, 6.76 g/L; IgG2, 2.29 g/L; IgG3, 0.27 g/L; IgG4, 0.37 g/L at 10–12 years of age; IgG1, 7.45 g/L; IgG2, 2.92 g/L; IgG3, 0.28 g/L; IgG4, 0.38 g/L at 13–16 years of age.

Conclusion

To our knowledge, this study is the first to establish RIs for serum IgG subclasses exclusively in Chinese children.

Deficit of IgG2 in HIV-positive pregnant women is responsible of inadequate IgG2 levels in their HIV-uninfected children in Malawi

BACKGROUND

Transplacental passage of IgGs is impaired in HIV + pregnant women, possibly determining an inadequate immunological protection in their children. We aimed to determine the impact of maternal immunological IgG profile and immunoactivation status on the efficiency of transplacental passage of IgG subclasses in HIV + mothers.

METHODS

16 mother/infants pairs were studied in Malawi. Mothers received antiretroviral therapy (ART) from the third trimester of pregnancy. Determinations of pre-ART levels of maternal sCD14, of IgG subclasses in mothers at delivery and in their 1-month-old infants, were performed using commercial ELISA kits.

RESULTS

At delivery, after a median of 10 weeks of ART, 12/16 mothers were hypergammaglobulinemic, with IgG levels (20.5 mg/ml, 95% CI:18.8-26.8) directly correlated to the plasmatic levels of sCD14 (r = 0.640, p = 0.014). IgG1 levels (17.9 mg/ml) accounted for 82% of IgG, IgG3 and IgG4 levels were in the normal range. A profound deficit of IgG2 was observed both in mothers (0.60 mg/ml) and in infants (0.14 mg/ml). Placental transfer ratio (range 0.16-0.42) did not show a selective impairment between the different IgG subclasses. The transplacental passage of all IgG subclasses was decreased in the presence of maternal IgG over 16 mg/ml (significantly for IgG1, p = 0.031) and of high levels of sCD14 (p = 0.063).

CONCLUSIONS

Transplacental passage was reduced for all IgG subclasses and inversely correlated to high levels of maternal IgGs and to the degree of immunoactivation. The profound depression of IgG2 in mothers suggests that IgG2 neonatal levels mostly reflect the maternal deficit rather than a selective impairment of IgG2 transfer.

Serum IgG subclass levels and risk of exacerbations and hospitalizations in patients with COPD

BACKGROUND

The literature is scarce regarding the prevalence and clinical impact of IgG subclass deficiency in COPD. We investigated the prevalence of IgG subclass deficiencies and their association with exacerbations and hospitalizations using subjects from two COPD cohorts.

METHODS

We measured IgG subclass levels using immunonephelometry in serum samples from participants enrolled in two previous COPD trials: Macrolide Azithromycin for Prevention of Exacerbations of COPD (MACRO; n = 976) and Simvastatin for the Prevention of Exacerbations in Moderate-to-Severe COPD (STATCOPE; n = 653). All samples were collected from clinically stable participants upon entry into both studies. IgG subclass deficiency was diagnosed when IgG subclass levels were below their respective lower limit of normal: IgG1 < 2.8 g/L; IgG2 < 1.15 g/L; IgG3 < 0.24 g/L; and IgG4 < 0.052 g/L. To investigate the impact of IgG subclass levels on time to first exacerbation or hospitalization, we log-transformed IgG levels and performed Cox regression models, with adjustments for confounders.

RESULTS

One or more IgG subclass deficiencies were found in 173 (17.7%) and 133 (20.4%) participants in MACRO and STATCOPE, respectively. Lower IgG1 or IgG2 levels resulted in increased risk of exacerbations with adjusted hazard ratios (HR) of 1.30 (95% CI, 1.10-1.54, p < 0.01) and 1.19 (95% CI, 1.05-1.35, p < 0.01), respectively in the MACRO study, with STATCOPE yielding similar results. Reduced IgG1 or IgG2 levels were also associated with increased risk of hospitalizations: the adjusted HR for IgG1 and IgG2 was 1.52 (95% CI: 1.15-2.02, p < 0.01) and 1.33 (95% CI, 1.08-1.64, p < 0.01), respectively for the MACRO study; in STATCOPE, only IgG2 was an independent predictor of hospitalization. In our multivariate Cox models, IgG3 and IgG4 levels did not result in significant associations for both outcomes in either MACRO or STATCOPE cohorts.

CONCLUSIONS

Approximately 1 in 5 COPD patients had one or more IgG subclass deficiencies. Reduced IgG subclass levels were independent risk factors for both COPD exacerbations (IgG1 and IgG2) and hospitalizations (IgG2) in two COPD cohorts.

TRIAL REGISTRATION

This study used serum samples from participants of the MACRO ( NCT00325897 ) and STATCOPE ( NCT01061671 ) trials.

Adult reference intervals for IgG subclasses with Siemens immunonephelometric assays in Chinese population

Objective

To determine the adult reference intervals for the Siemens IgG subclass reagents.

Methods

636 blood samples of healthy adults were analyzed to determine the level of IgG subclass using the reagents of Siemens immunonephelometric assay with molecular biology kits.

Results

IgGSc reference intervals were as follows: IgG1 4.45–9.76 g/L, IgG2 2.07–8.57 g/L, IgG3 0.08–0.80 g/L and IgG4 0.05–1.54 g/L. There was an excellent correlation between the total IgG and the sum of the IgG subclasses. No significant gender and age differences were observed.

Conclusions

Our data provide the missing reference intervals and enable the use of the nephelometric IgG subclass reagents in Chinese. The study can offer reference on clinic diagnose.

IgG subclasses quantitation: Analytical performance of The Binding Site SPAPLUS® human assay and comparison with Siemens BNII® assay

OBJECTIVES

Accurate evaluation of analyzers is highly recommended before these devices are broadly introduced for routine testing. Concerning quantification of IgG subclasses (IgGSc), standardization has not yet been reached and thus different assays might lead to different results. Here we report the analytical performances of The Binding Site (TBS) SPA_PLUS® human IgGSc assay and the concordance with the Siemens BNII® human IgGSc assay.

DESIGN AND METHODS

We evaluated precision, LoB, LoD and linearity of TBS SPA_PLUS® human IgGSc immunoassay. Quantitation of IgGSc in 53 patients' serum samples was performed in parallel on both analyzers. Results from both assays were compared.

RESULTS

Analytical performances of the TBS SPA_PLUS® human IgGSc assay are acceptable for routine clinical use. According to the method comparison study, TBS assay measures lower values than Siemens assay for IgG1 and IgG4, whereas for IgG2 and IgG3 TBS provides greater values. All assays present a proportional bias, greater in the case of IgG3 and IgG4 assays. Individual subclass agreement, based on the classification of samples within three categories (low, normal and high) according to assay-specific reference intervals, range from 75% (IgG1) to 92% (IgG2). However, total classification agreement over all four subclasses only account for 55% of samples.

CONCLUSION

Results obtained from both assays are not interchangeable. Standardization of IgGSc assay and review of the reference ranges must be accomplished in order to achieve a higher degree of agreement between different methods.

IgG subclass deficiencies in children: Facts and fiction

The chance to analyse the four IgG subclasses arose with the publication of Terry and Fahey¹ . Since then, a lot of new information on the role of subclasses and their deficiency states in humans has been obtained. This review tries to analyse critically our current knowledge of subclass deficiencies in children.

Detection of drug-responsive B lymphocytes and antidrug IgG in patients with β-lactam hypersensitivity

BACKGROUND

Delayed-type β-lactam hypersensitivity develops in subset of patients. The cellular immunological processes that underlie the drug-specific response have been described; however, little is known about involvement of the humoral immune system. Thus, the aim of this study was to utilize piperacillin hypersensitivity as an exemplar to (i) develop cell culture methods for the detection of drug-specific B-cell responses, (ii) characterize drug-specific IgG subtypes and (iii) assess reactivity of IgG antibodies against proteins modified to different levels with piperacillin haptens.

METHODS

IgG secretion and CD19⁺ CD27⁺ expression on B cells were measured using ELISPOT and flow cytometry, respectively. A piperacillin-BSA adduct was used as an antigen in ELISA antibody binding studies. Adducts generated using different ratios of drug to protein were used to determine the degree of conjugation required to detect IgG binding.

RESULTS

B cells from hypersensitive patients, but not controls, were stimulated to secrete IgG and increase CD27 expression when cultured with soluble piperacillin. A piperacillin-BSA adduct with cyclized and hydrolysed forms of the hapten bound to eight lysine residues was used to detect hapten-specific IgG 1-4 subclasses in patient plasma. Hapten inhibition and the use of structurally unrelated hapten-BSA adducts confirmed antigen specificity. Antibody binding was detected with antigens generated at piperacillin/BSA ratios of 10:1 and above, which corresponded to a minimum epitope density of 1 for antibody binding.

CONCLUSION

These data show that antigen-specific B lymphocytes and T lymphocytes are activated in piperacillin-hypersensitive patients. Further work is needed to define the role different IgG subtypes play in regulating the iatrogenic disease.

IgA and IgM protein primarily drive plasma corona-induced adhesion reduction of PLGA nanoparticles in human blood flow

The high abundance of immunoglobulins (Igs) in the plasma protein corona on poly(lactic-co-glycolic) acid (PLGA)-based vascular-targeted carriers (VTCs) has previously been shown to reduce their adhesion to activated endothelial cells (aECs) in human blood flow. However, the relative role of individual Ig classes (e.g., IgG, IgA, and IgM) in causing adhesion reduction remains largely unknown. Here, we characterized the influence of specific Ig classes in prescribing the binding efficiency of PLGA nano-sized VTCs in blood flow. Specifically, we evaluated the flow adhesion to aECs of PLGA VTCs with systematic depletion of various Igs in their corona. Adhesion reduction was largely eliminated for PLGA VTCs when all Igs were removed from the corona. Furthermore, re-addition of IgA or IgM to the Igs-depleted corona reinstated the low adhesion of PLGA VTCs, as evidenced by ∼40-70% reduction relative to particles with an Igs-deficient corona. However, re-addition of a high concentration of IgG to the Igs-depleted corona did not cause significant adhesion reduction. Overall, the presented results reveal that PLGA VTC adhesion reduction in blood flows is primarily driven by high adsorption of IgA and IgM in the particle corona. Pre-coating of albumin on PLGA VTCs mitigated the extent of adhesion reduction in plasma for some donors but was largely ineffective in general. Overall, this work may shed light into effective control of protein corona composition, thereby enhancing VTC functionality in vivo for eventual clinical use.