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

High-Coverage Disulfide Mapping Enabled by Programmable Disulfide-Ene Reaction Integrated onto a Bottom-Up Protein Analysis Workflow

Mapping disulfide linkages is crucial for characterizing pharmaceutical proteins during drug development and quality control. Traditional bottom-up protein analysis workflows often suffer from incomplete mapping for tryptic peptides consisting of multiple disulfide bonds. Although the employment of a partial reduction of disulfide bonds can improve disulfide mapping, it becomes a bottleneck of analysis because individual tuning is often needed. Herein, we have developed an online disulfide-ene reaction system in which the composition of the reaction solvent can be programmed to achieve optimal partial reduction of tryptic disulfide peptides after liquid chromatography separation. By coupling this system onto a bottom-up protein analysis workflow, high coverage for sequencing (71-83%) and disulfide mapping (84-100%) was achieved for standard proteins consisting of 4-19 disulfide bonds. The analytical capability was further demonstrated by mapping 13 scrambled disulfide bonds in lysozyme and achieving compositional analysis of IgG isotypes (κ and λ) and subclasses (IgG1-IgG4) from human plasma.

Immunoglobulin G4 in primary Sjögren's syndrome and IgG4-related disease - connections and dissimilarities

Primary Sjögren's syndrome (pSS) is an autoimmune disease, with B cell hyperactivation and autoantibody production as its immunological hallmarks. Although the distinction between immunoglobulin G4-related disease (IgG4-RD) and pSS, based on the presence or absence of certain autoantibodies, seems easy to make, possibility of elevated serum IgG4 concentration and often similar organ involvement may lead to a misdiagnosis. The increased serum concentration of IgG4 in IgG4-RD is not clearly linked to the pathogenesis of IgG-RD and it has been suggested that it may constitute just an epiphenomenon. The aim of this article is to discuss the presence of IgG4 in pSS and IgG4-RD and its potential significance for these two diseases.

Nano-Photonic Crystal D-Shaped Fiber Devices for Label-Free Biosensing at the Attomolar Limit of Detection

Maintaining both high sensitivity and large figure of merit (FoM) is crucial in regard to the performance of optical devices, particularly when they are intended for use as biosensors with extremely low limit of detection (LoD). Here, a stack of nano-assembled layers in the form of 1D photonic crystal, deposited on D-shaped single-mode fibers, is created to meet these criteria, resulting in the generation of Bloch surface wave resonances. The increase in the contrast between high and low refractive index (RI) nano-layers, along with the reduction of losses, enables not only to achieve high sensitivity, but also a narrowed resonance bandwidth, leading to a significant enhancement in the FoM. Preliminary testing for bulk RI sensitivity is carried out, and the effect of an additional nano-layer that mimics a biological layer where binding interactions occur is also considered. Finally, the biosensing capability is assessed by detecting immunoglobulin G in serum at very low concentrations, and a record LoD of 70 aM is achieved. An optical fiber biosensor that is capable of attaining extraordinarily low LoD in the attomolar range is not only a remarkable technical outcome, but can also be envisaged as a powerful tool for early diagnosis of diseases.

An acute rheumatic fever immune signature comprising inflammatory markers, IgG3, and Streptococcus pyogenes-specific antibodies

Understanding the immune profile of acute rheumatic fever (ARF), a serious post-infectious sequelae of Streptococcal pyogenes (group A Streptococcus [GAS]), could inform disease pathogenesis and management. Circulating cytokines, immunoglobulins, and complement were analyzed in participants with first-episode ARF, swab-positive GAS pharyngitis and matched healthy controls. A striking elevation of total IgG3 was observed in ARF (90% > clinical reference range for normal). ARF was also associated with an inflammatory triad with significant correlations between interleukin-6, C-reactive protein, and complement C4 absent in controls. Quantification of GAS-specific antibody responses revealed that subclass polarization was remarkably consistent across the disease spectrum; conserved protein antigens polarized to IgG1, while M-protein responses polarized to IgG3 in all groups. However, the magnitude of responses was significantly higher in ARF. Taken together, these findings emphasize the association of exaggerated GAS antibody responses, IgG3, and inflammatory cytokines in ARF and suggest IgG3 testing could beneficially augment clinical diagnosis.

Suboptimal Response to Biologics in Severe Asthma-A Marker of Humoral Immunodeficiencies

BACKGROUND

Asthmatic patients with antibody deficiencies (AD) have more severe disease and higher risk of exacerbations. No data exist about the efficacy of biologics in severe asthma (SA) patients with AD.

OBJECTIVE

To evaluate the efficacy of biologics in SA patients with and without AD.

METHODS

A case-control real-life study was conducted including 68 patients divided into 2 groups: group 1 with SA-AD and group 2 with SA.

RESULTS

Treatment with biologics for 6 months was effective for decreasing the number of exacerbations, hospitalizations, and emergency department (ED) visits and improving the Asthma Control Questionnaire (ACQ) score; biologics also proved a systemic corticosteroid-sparing effect. Despite benefits, the number of exacerbations, hospitalizations, and ED visits, the mean ACQ score, and the cumulative dose of systemic corticosteroids remain higher in group 1 than in group 2, with lower lung function parameters. The rates of responses in group 1 were inferior to those in group 2, with a decrease by ≥50% of exacerbation rate in 76% versus 97% of patients (P = .006), no hospitalization in 44% versus 91% of patients (P < .001), no ED visit in 56% versus 82% of patients (P = .018), a significant improvement of the ACQ score by ≥0.5 in 68% versus 100% of patients (P < .001), and an increase of forced expiratory volume in the first second by >10% in 32% versus 65% of patients (P = .007).

CONCLUSIONS

Despite evident benefits, SA patients with AD have suboptimal responses to biologics compared with those immunocompetent. A multidisciplinary approach is necessary to optimize the management of these patients in practice.

Comparison of the Efficacy of Longer versus Shorter Pulsed High Dose Dapsone Combination Therapy in the Treatment of Chronic Lyme Disease/Post Treatment Lyme Disease Syndrome with Bartonellosis and Associated Coinfections

Twenty-five patients with relapsing and remitting Borreliosis, Babesiosis, and bartonellosis despite extended anti-infective therapy were prescribed double-dose dapsone combination therapy (DDDCT), followed by one or several courses of High Dose Dapsone Combination Therapy (HDDCT). A retrospective chart review of these 25 patients undergoing DDDCT therapy and HDDCT demonstrated that 100% improved their tick-borne symptoms, and patients completing 6-7 day pulses of HDDCT had superior levels of improvement versus 4-day pulses if Bartonella was present. At the completion of treatment, 7/23 (30.5%) who completed 8 weeks of DDDCT followed by a 5-7 day pulse of HDDCT remained in remission for 3-9 months, and 3/23 patients (13%) who recently finished treatment were 1 ½ months in full remission. In conclusion, DDDCT followed by 6-7 day pulses of HDDCT could represent a novel, effective anti-infective strategy in chronic Lyme disease/Post Treatment Lyme Disease Syndrome (PTLDS) and associated co-infections, including Bartonella, especially in individuals who have failed standard antibiotic protocols.

Association of serum IgG4 and disease outcomes in patients with inflammatory bowel disease

Background

The etiology of inflammatory bowel disease (IBD) is multifactorial and thought to be influenced by inappropriate activation of the gut mucosal immune system. As the only immunoglobulin G (IgG) subclass unable to activate the classical complement cascade, the role of IgG4 in IBD pathophysiology as an immunomodulator is controversial. This study aimed to determine the association of low, normal and high IgG4 levels with the outcomes of IBD patients.

Methods

This was a retrospective study of a multisite tertiary care center database evaluating patients with IBD who had an IgG4 level drawn between 2014 and 2021. Subjects were divided into low, normal, and high IgG4 level groups for evaluation of demographic and clinical indicators of IBD activity and severity.

Results

Of 284 patients with IBD, 22 had low (7.7%), 16 high (5.6%), and 246 (86.6%) normal IgG4 levels. There was no difference in IBD subtype, mean age, age at IBD diagnosis, or smoking between the 3 groups. There was no difference in number of hospitalizations (P=0.20), C-reactive protein levels, need for intestinal resection (P=0.85), or presence of primary sclerosing cholangitis (P=0.15), pancreatitis (P=0.70), or perianal disease (P=0.68) between the groups. Significantly more patients in the low IgG4 group had previous exposure to vedolizumab compared to the other groups and more patients in the low IgG4 group received vedolizumab (P=0.04), azathioprine (P=0.04) and prednisone (P=0.03) during the 5-year follow up.

Conclusion

In this study, a low serum IgG4 level was associated with higher rates of vedolizumab, azathioprine, and steroid use.

Salmonella Typhi Vaccination Response as a Tool for the Stratification of Risk in Patients with Predominantly Antibody Deficiencies

Predominantly antibody deficiencies are the most frequent type of primary immunodeficiency (PID). Diagnosis requires evaluation of the immune function by distinguishing the presence or absence of a response against polysaccharide antigens. Salmonella enterica serovar Typhi-based vaccines have proved to be a suitable tool. We studied a group of patients with suspicion of primary immunodeficiency and classified them by final diagnosis. We analyzed the vaccination response to S. Typhi and other immune biomarkers and clinical data. The aim of this study was to classify patients regarding the intensity of their immune response measured as the difference between specific immunoglobulin G levels before and after vaccination and antibody levels in the post-vaccination sample in order to improve clinical decisions regarding follow up and treatment of immunodeficiency patients. We established four groups of response: Non responders (NR), Low responders (LR), Intermediate responders (IR), and High responders (HR), where we found differences in IgG, IgG1, IgG2, IgG4, IgA, IgA1, IgA2, and IgM, and where the finally achieved diagnosis was also different and corresponding to the level of vaccination response.

Comparison of different sets of immunological tests to identify treatable immunodeficiencies in adult bronchiectasis patients

Background

The reported prevalence of immunodeficiencies in bronchiectasis patients is variable depending on the frequency and extent of immunological tests performed. European Respiratory Society guidelines recommend a minimum bundle of tests. Broadening the spectrum of immunological tests could increase the number of patients diagnosed with an immunodeficiency and those who could receive specific therapy. The primary objective of the present study was to assess the performance of different sets of immunological tests in diagnosing any, primary, secondary or treatable immunodeficiencies in adults with bronchiectasis.

Methods

An observational, cross-sectional study was conducted at the Bronchiectasis Program of the Policlinico University Hospital in Milan, Italy, from September 2016 to June 2019. Adult outpatients with a clinical and radiological diagnosis of bronchiectasis underwent the same immunological screening during the first visit when clinically stable consisting of: complete blood count; immunoglobulin (Ig) subclass tests for IgA, IgG, IgM and IgG; total IgE; lymphocyte subsets; and HIV antibodies. The primary endpoint was the prevalence of patients with any immunodeficiencies using five different sets of immunological tests.

Results

A total of 401 bronchiectasis patients underwent the immunological screening. A significantly different prevalence of bronchiectasis patients diagnosed with any, primary or secondary immunodeficiencies was found across different bundles. 44.6% of bronchiectasis patients had a diagnosis of immunodeficiency when IgG subclasses and lymphocyte subsets were added to the minimum bundle suggested by the guidelines.

Conclusion

A four-fold increase in the diagnosis of immunodeficiencies can be found in adults with bronchiectasis when IgG subclasses and lymphocyte subsets are added to the bundle of tests recommended by guidelines.

Advection-Enhanced Kinetics in Microtiter Plates for Improved Surface Assay Quantitation and Multiplexing Capabilities

Surface assays such as ELISA are pervasive in clinics and research and predominantly standardized in microtiter plates (MTP). MTPs provide many advantages but are often detrimental to surface assay efficiency due to inherent mass transport limitations. Microscale flows can overcome these and largely improve assay kinetics. However, the disruptive nature of microfluidics with existing labware and protocols has narrowed its transformative potential. We present WellProbe, a novel microfluidic concept compatible with MTPs. With it, we show that immunoassays become more sensitive at low concentrations (up to 9× signal improvement in 12× less time), richer in information with 3-4 different kinetic conditions, and can be used to estimate kinetic parameters, minimize washing steps and non-specific binding, and identify compromised results. We further multiplex single-well assays combining WellProbe's kinetic regions with tailored microarrays. Finally, we demonstrate our system in a context of immunoglobulin subclass evaluation, increasingly regarded as clinically relevant.

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%.

Immunoglobulin G Deficiency in Children with Recurrent Respiratory Infections with and Without History of Allergy

Recurrent respiratory tract infections (RTI) are one of the most common diseases in childhood. Frequent infections adversely affect the development of a child and may lead to suspicion of immunodeficiency. An additional allergy component is thought conducive to infection occurrence. In this study, we retrospectively assessed medical records of 524 children hospitalized with RTI. Patients were divided into two groups: RTI-alone (n = 394) and RTI with a history of allergy (n = 130). Overall, we found that a great majority of children with RTI had the immunoglobulin G within the normal limit, irrespective of allergy. A variable IgG deficiency, most often affecting IgG1, IgG3, and IgG4 subclass, was present in less than one-third of children. Proportions of specific IgG subclass deficiency, varying from about 10% to 40%, were similar in both RTI-alone and RTI-allergy groups. The only significant effect was a modestly smaller proportion of children with IgG4 deficiency in the RTI-allergy group when compared with the RTI-alone group. We also found that IgG deficiencies were age-dependent as their number significantly increased with children's age, irrespective of allergy. The results demonstrate a lack of distinct abnormalities in the immunoglobulin G profile which would be characteristic to a clinical history of allergy accompanying recurrent RTI in children. Thus, we conclude that the assessment of IgGs could hardly be of help in the differential diagnostics of the allergic background of RTI.

Impact of Tocilizumab (Anti-IL-6R) Treatment on Immunoglobulins and Anti-HLA Antibodies in Kidney Transplant Patients With Chronic Antibody-mediated Rejection

BACKGROUND

Chronic antibody-mediated rejection (cAMR) results in the majority of renal allograft losses. Currently, there are no approved therapies. We recently reported on clinical use of tocilizumab (TCZ) for treatment of cAMR in HLA-sensitized kidney transplant patients. IgG1 and IgG3 subclasses of IgG are potent effectors of complement- and antibody-dependent cellular cytotoxicity, which are critical mediators of AMR. Here, we examined the impact of TCZ treatment for cAMR on total IgG, IgG1-4 subclasses, and anti-HLA-IgG (total and subclasses).

METHODS

Archived plasma obtained pre- and post-TCZ treatment (8 mg/kg, 6×, monthly) from 12 cAMR patients who failed standard of care treatment with intravenous immune globulin + rituximab with or without plasma exchange were tested for total IgG and IgG1-4 by ELISA, anti-HLA-total IgG, IgG3 and IgG4, and donor-specific antibody by Luminex assay. Archived plasma from 14 cAMR patients treated with the standard of care were included as controls.

RESULTS

Total IgG and IgG1-3 were significantly reduced post-TCZ, whereas no reduction was seen post-treatment in the control group. Of 11 patients, 8 (73%) showed reduction of anti-HLA-total IgG and IgG3 post-TCZ, but this was not statistically significant.

CONCLUSIONS

TCZ reduced total IgG and IgG1-3 and anti-HLA-total IgG and IgG3 levels, suggesting that TCZ suppresses Ig production in B cells nonspecifically, likely through inhibition of interleukin 6-mediated signaling to B cells and plasma cells. This may be a contributing factor for the beneficial effect of TCZ on cAMR observed in this patient population.

Immunoglobulin G and immunoglobulin G subclass concentrations differ according to sex and race

BACKGROUND

Serum immunoglobulin G (IgG) concentrations are integral to the workup of immune deficiencies and IgG4-related disease (IgG4-RD). Demographic differences in IgG concentrations are poorly described but can influence test interpretation, contribute to racial disparities in primary immunodeficiency diagnosis, and explain demographic differences in IgG concentrations in IgG4-RD.

OBJECTIVE

To assess differences in IgG and IgG subclass concentrations according to sex and race.

METHODS

We identified patients with IgG and IgG subclass concentrations measured in a large health care system. Multivariate-adjusted differences in IgG and IgG subclass concentrations and the proportion of subjects with results outside of reference ranges according to sex and race were estimated.

RESULTS

Of the 12,851 patients, the mean age was 54.7 years and 7917 (62%) were female. Of these, 11,673 (91%) were white, 611 (5%) were black, and 302 (2%) were Asian. Compared with the mean concentrations of white patients, Asian and black patients had higher mean concentrations of IgG (1340.0 and 1504.4 vs 988.1 mg/dL, P < .001), IgG1 (782.0 and 938.4 vs 592.4 mg/dL, P < .001), IgG2 (493.5 and 384.2 vs 305 mg/dL, P < .001), IgG3 (76.6 and 91.9 vs 55.9 mg/dL, P < .001), and IgG4 (140.4 and 53.6 vs 41.6 mg/dL, P < .001). Immunoglobin G subclass 4 concentrations were higher in males than those in females (56.3 vs 37.4 mg/dL, P < .001). Similar observations were made when comparing the proportions of patients with results outside of reference ranges and after stratifying by diagnosis.

CONCLUSION

Immunoglobin G and IgG subclass concentrations differ according to sex and race. These findings may have implications for the interpretation of these test results but require confirmation in diverse, healthy populations.

Physiological role of plasma and its components and the clinical implications of different methods of apheresis: A narrative review

Nowadays, therapeutic plasmapheresis (TP) is accepted as part of the treatment for specific groups of diseases. The availability of different methods, including double filtration and adsorption, increases selectivity for the removal of substances. However, the use of these techniques requires a thorough understanding of the characteristics and components of plasma. By considering pivotal papers from several databases, the aim of this narrative review is to describe the characteristics of plasma related to apheresis techniques. We have tried to cover the clinical implications including physiology, estimation of plasma volume, viscosity, and a description of its components including the size, volume of distribution, and half-lives of the different substances to be removed or maintained depending on the clinical situation and applied apheresis technique. Applying this knowledge will help us to choose the right method and dosage and improve the efficacy of the procedure by preventing or addressing any complications.

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.

Reconstitution of IgG Subclasses following Immunoglobulin Therapy in Adult Primary Hypogammaglobulinemia

BACKGROUND

Immunoglobulin (Ig) therapy is highly effective in reducing the frequency and severity of infections. However, a subset of patients does not respond adequately.

OBJECTIVE

To determine in adult patients with primary hypogammaglobulinemia (a) if failure to reconstitute IgG subclass(es) is associated with inadequate clinical response, (b) whether reconstitution of IgG subclasses differs between routes of Ig administration, (c) which subclasses contribute to low total IgG, and (d) what are the most commonly impaired Streptococcus pneumoniae serotypes.

METHODS

A retrospective review of the records of patients with primary hypogammaglobulinemia followed up at the Immunology Clinic between 2010 and 2018 was conducted. Demographic, clinical, and laboratory data were collected.

RESULTS

Seventy-one patients with primary hypogammaglobulinemia were included. All subclasses were reconstituted in 85% of the patients. IgG3 and IgG4 were most commonly not reconstituted. Reconstitution occurred in 85% of the patients on intravenous Ig (IVIG), 81% of the patients on conventional subcutaneous Ig (SCIG), and 100% of the patients on enzyme-facilitated subcutaneous Ig (fSCIG). The annual infection rate was 0.87 with IVIG, 0.88 with conventional SCIG, and 0.6 with fSCIG. IgG subclasses contributing to low total IgG included IgG1 (61%), IgG2 (49%), IgG3 (23%), and IgG4 (28%). In patients with concomitant specific antibody deficiency (n = 47), the most commonly impaired antibody responses were against pneumococcal serotypes 3, 4, 6b, 12f, and 23f.

CONCLUSIONS

Failure to reconstitute subclasses does not correlate with an inadequate clinical response to immunoglobulin therapy in primary hypogammaglobulinemia. Full reconstitution of IgG subclasses was observed with fSCIG. A smaller panel of pneumococcal antibody responses may be used to define specific antibody deficiency.

Appropriate lung management in patients with primary antibody deficiencies

Introduction: Human primary immunodeficiency diseases (PIDs) include a broad spectrum of more than 350 disorders, involving different branches of the immune system and classified as 'rare diseases.' Predominantly antibody deficiencies (PADs) represent more than half of the PIDs diagnosed in Europe and are often diagnosed in the adulthood. Areas covered: Although PAD could first present with autoimmune or neoplastic features, respiratory infections are frequent and respiratory disease represents a relevant cause of morbidity and mortality. Pulmonary complications may be classified as infection-related (acute and chronic), immune-mediated, and neoplastic. Expert opinion: At present, no consensus guidelines are available on how to monitor and manage lung complications in PAD patients. In this review, we will discuss the available diagnostic, prognostic and therapeutic instruments and we will suggest an appropriate and evidence-based approach to lung diseases in primary antibody deficiencies. We will also highlight the possible role of promising new tools and strategies in the management of pulmonary complications. However, future studies are needed to reduce of diagnostic delay of PAD and to better understand lung diseases mechanisms, with the final aim to ameliorate therapeutic options that will have a strong impact on Quality of Life and long-term prognosis of PAD patients.

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.

Identification of IgG3-specific epitope that remedies problem in diagnostic IgG subclass determination due to human genetic variation

There are four subtypes of human IgG with different effector functions. Quantifying the relative amount of each IgG subtype is important for laboratory diagnosis in multiple settings. However, in an evolving landscape of the appreciation of human variability and the need for precision/personalised laboratory diagnosis, it has also been shown that there are numerous natural variants of IgG subtypes, with at least 29 having been described. It has recently been reported that commercially available polyclonal antisera to IgG3 cross react with variants of other IgG subtypes, while available monoclonal anti-IgG3 have a blind-spot for the IgG3-04 variant. Herein, we report that IgG3-04 contains an epitope in common with all known IgG3 variants and absent in other subtypes. A novel monoclonal anti-IgG3 is described that is specific to IgG3 but without any blind-spots for known IgG3 variants, providing a remedy to the problem of genetic variability of IgG3.