A Özön, SA Çamlar, G Erfidan, ÖÖ Şimşek, C Başaran, D Alaygut, F Mutlubaş, D Yılmaz, BK Demir

Abstract

Objectives: Nephrotic syndrome (NS) may lead to the loss of protective antibodies against infectious agents as a consequence of its underlying pathophysiology. This study aimed to evaluate immunoglobulin G levels specific to measles, mumps, rubella, and varicella in children with NS in remission. Methods: Children aged 2-18 years with NS who had completed the national immunisation schedule and were in remission were included. Exclusion criteria were age under two years, proteinuria, current infection, documented immunodeficiency, or incomplete vaccination. Seropositivity was defined using the following thresholds: >100 mIU/mL for varicella, >10 IU/mL for rubella, >250 mIU/mL for measles, and >25 mIU/mL for mumps. Results: Thirty-nine patients were included (51.4% male), with a median age of 13 years (range 3.7-18). Median follow-up duration was 50 months (range 12-120), and the mean number of relapses was 5.38 (range 1-17). Seropositivity rates were 56.4% for measles, 69.2% for rubella, 43.6% for mumps, and 71.8% for varicella. Patients receiving combined corticosteroid and immunosuppressive therapy showed lower seropositivity rates than those receiving corticosteroids alone; however, these differences were not statistically significant. Conclusion: Vaccine-induced immunity in children with NS may be compromised by both disease-related factors and immunosuppressive treatment. Periodic monitoring of vaccine-specific antibodies may be warranted during follow-up.

Introduction

Nephrotic syndrome (NS) is the most common glomerular disease in childhood and is associated with impairment of both cellular and humoral immunity, including hypogammaglobulinaemia.¹ As a consequence, children with NS have an increased susceptibility to bacterial and viral infections. Reduced serum immunoglobulin G (IgG) levels and decreased concentrations of complement factor B and D have also been reported.^2-4 Viral infections, particularly varicella-zoster virus (VZV), are also more frequently encountered in this population and may trigger disease relapses through immune activation.⁵

Vaccination is a cornerstone of infection prevention; however, impaired T- and B-cell function and hypogammaglobulinaemia may result in reduced vaccine responsiveness in children with NS.⁶ Seropositivity, defined as antibody titres exceeding a predefined protective threshold, is commonly used as a surrogate marker of immunity.⁷ Nevertheless, protective immunity also depends on immunological memory and cell-mediated responses, which are not routinely assessed in clinical practice.⁸ Consequently, most studies rely on serological antibody measurements to evaluate vaccine-induced immunity.⁹ This study aimed to assess seropositivity for measles, rubella, mumps, and varicella in children with idiopathic NS who were in clinical remission.

Methods

This retrospective observational study included children with idiopathic nephrotic syndrome (INS) followed at our centre between November 2018 and June 2021. Eligible patients were in remission, had completed routine childhood immunisation (two doses of measles–mumps–rubella vaccine and one dose of varicella vaccine), and had no active infection at the time of assessment. Exclusion criteria were age under two years, ongoing proteinuria, incomplete vaccination records, active infection, or known primary or secondary immunodeficiency. Patient selection is presented in a STROBE-compliant flow diagram (Figure 1).

Figure 1 STROBE-compliant flow diagram illustrating the patient selection process, inclusion criteria, and final study population of children with nephrotic syndrome.

Demographic and clinical data included age, sex, age at diagnosis, duration of follow-up, number of relapses, and current or previous immunosuppressive treatments (corticosteroids, cyclophosphamide, cyclosporine, rituximab, and mycophenolate mofetil). Histopathological diagnoses were recorded for patients who had undergone renal biopsy.

Laboratory parameters comprised complete blood count, serum biochemistry (urea, creatinine, albumin, cholesterol), inflammatory markers, and total immunoglobulin levels (IgA, IgG, IgM). Vaccine-specific IgG titres for measles, mumps, rubella, and VZV were measured using standardised enzyme-linked immunosorbent assay and chemiluminescence-based methods. The following analysers were used: the Roche Cobas 6000, Roche Hitachi 917, Cobas e411 (Roche Diagnostics), and the Siemens IMMULITE 2000 XPi Immunoassay System (Siemens Healthcare Diagnostics). Seropositivity was defined based on serum IgG levels as follows: >100 mIU/mL for VZV, >250 mIU/mL for measles, >10 IU/mL for rubella, and >25 mIU/mL for mumps. Cases with IgG levels falling within the grey zone were classified as seronegative.

Patients were classified as having steroid-sensitive or steroid-resistant NS according to Kidney Disease: Improving Global Outcomes (KDIGO) and International Pediatric Nephrology Association (IPNA) guidelines.¹⁰ Subgroup analyses were also performed based on treatment exposure.

Statistical Analysis
Descriptive statistics were expressed as mean ± standard deviation (SD) for normally distributed variables, and as median (interquartile range) for non-normally distributed variables. The distribution of variables was assessed using the Shapiro–Wilk test. For the comparison of independent quantitative variables, the independent samples t-test was applied to normally distributed data, while the Mann–Whitney U test was used for non-normally distributed data. Categorical variables were analysed using the Chi-square test. All statistical analyses were performed using SPSS Statistics version 24.0 (IBM Corp., Armonk, NY, USA). A p-value of less than 0.05 was considered statistically significant.

Results

A total of 39 patients aged 3-18 years were enrolled in the study. Demographic characteristics are summarised in Table 1. Renal biopsy findings were available for 29 patients and included minimal change disease (43.3%), focal segmental glomerulosclerosis (20%), membranoproliferative glomerulonephritis (10%), membranous glomerulonephritis (3.3%), C3 glomerulonephritis (3.3%), IgM nephropathy (13.3%), and IgA nephropathy (6.7%). Based on serum IgG levels, seropositivity for MMR, and VZV was detected in 22 (56.4%), 27 (69.2%), 17 (43.6%), and 28 (71.8%) patients, respectively.

At the time of the first relapse of NS, all treatments received by the patients prior to the relapse were retrospectively reviewed. Thirteen patients (33.0%) were treated with corticosteroids alone, while 15 patients (38.5%) received a combination of corticosteroids and cyclosporine. In addition, four patients (10.3%) were treated with corticosteroids, cyclosporine, and rituximab; two patients (5.1%) received corticosteroids, cyclosporine, and mycophenolate mofetil; two patients (5.1%) received corticosteroids, cyclosporine, and cyclophosphamide; and three patients (7.7%) were treated with corticosteroids and cyclophosphamide. During the study period, treatment status was retrospectively assessed. Seventeen patients (43.6%) were not receiving any active treatment, three patients (7.7%) were receiving corticosteroids alone, three patients (7.7%) were receiving corticosteroids in combination with cyclophosphamide, seven patients (17.9%) were receiving corticosteroids and cyclosporine, three patients (7.7%) were treated with corticosteroids in combination with other immunosuppressive agents, and six patients (15.4%) were receiving immunosuppressive therapy without corticosteroids.

Based on steroid responsiveness, 31 patients (79.5%) were classified as having steroid-sensitive nephrotic syndrome (SSNS), while 8 patients (20.5%) were classified as having steroid-resistant nephrotic syndrome (SRNS). Among SSNS cases, 17 patients (54.8%) exhibited a steroid-dependent or frequently relapsing course. There was no significant difference in mean age between patients with SRNS (12.61±4.6 years) and those with SSNS (12.38±3.9 years) (p=0.895).

Seropositivity rates for measles-mumps-rubella and varicella did not differ significantly between the SSNS and SRNS patients (Table 2). Although lower seropositivity rates were observed among patients receiving combined immunosuppressive therapy compared with corticosteroid monotherapy, these differences did not reach statistical significance (Table 3). No significant associations were found between seropositivity and pulse corticosteroid use or number of relapses.

Discussion

NS represents a leading cause of glomerular disease in childhood and is associated with impairment of both cellular and humoral immunity. This includes hypogammaglobulinaemia, which may compromise the persistence of vaccine-induced antibodies.^10-13 In our cohort, total IgG levels tended to correlate with seronegativity; however, this did not reach statistical significance, likely owing to the limited sample size. Alongside disease-related immunoglobulin loss, prolonged or intensive immunosuppressive therapy may further contribute to declining antibody levels over time, thereby increasing susceptibility to vaccine-preventable infections.^9,14-17 In this study, we evaluated seropositivity rates for MMR, and VZV in children with NS who had completed the national immunisation schedule and were in clinical remission. Overall, seropositivity rates for all four live attenuated vaccines were lower than expected, consistent with previous studies reporting waning seroprotection in this population.^13,14 These findings support the concept that vaccination during early childhood may not guarantee long-term seroprotection in the context of chronic immune dysfunction.¹ Notably, mumps IgG seropositivity was lower than that observed for measles and rubella. This observation is consistent with existing evidence indicating that the mumps component of the MMR vaccine is less immunogenic and associated with more rapid waning of antibody titres, even in healthy populations. In children with NS, disease-related hypogammaglobulinaemia and immunosuppressive treatments may further impair the generation and maintenance of long-term mumps-specific antibody responses. This may contribute to increasing seronegativity over time.

Vaccine effectiveness is defined as the ability of a vaccine to confer protection against a seesfectious agent. Seropositivity–defined as an antibody titre exceeding a predefined protective threshold–is commonly used as a surrogate marker of immunity.⁷ However, the interpretation of vaccine-specific IgG levels in paediatric patients is complicated by the lack of well-validated protective antibody thresholds for this population. Moreover, measured IgG concentrations do not assess functional neutralising antibody activity or cell-mediated immunity. Both may remain preserved despite low or undetectable serum IgG levels, especially following live attenuated vaccination.^8-10 Despite their importance, the routine assessment of cell-mediated immunity remains challenging in daily clinical practice. Therefore, as in many previous studies, we assessed serological antibody responses as a measure of vaccine-induced immunity.

Immunosuppressive therapies are frequently required in the management of NS; however, these treatments may adversely affect vaccine-induced protection against infections.⁹ In NS, antibody production is thought to be reduced, and seropositive individuals may lose protective antibody levels more rapidly than the healthy population. Reduction in antibody titres against live attenuated vaccines, including MMR and VZV, have been reported following immunosuppressive therapy.^13,18-21 Although seropositivity rates in our cohort tended to be lower among patients receiving combined corticosteroid and other immunosuppressive therapies compared with corticosteroid monotherapy, these differences were not statistically significant. Similarly, no significant differences were observed between steroid-sensitive and steroid-resistant NS groups. This likely reflects the small number of patients with steroid-resistant disease and the inclusion of frequently relapsing and steroid-dependent patients within the steroid-sensitive group.¹⁶ Limited data on rituximab-treated patients precluded meaningful subgroup analysis, although seropositivity rates tended to be lower in this subset.^22,23

Our study represents one of the few studies evaluating measles, rubella, mumps, and varicella IgG levels in paediatric patients with NS. The reduced seropositivity observed across all four live attenuated vaccines may reflect urinary IgG loss – a well-recognised feature of NS pathophysiology – as well as the immunosuppressive effects of corticosteroids and other immunosuppressive therapies used in disease management.

This study has several limitations. The cross-sectional, single-centre design and relatively small sample size limited statistical power and precluded longitudinal assessment of antibody dynamics. Additionally, baseline (pre-diagnosis) antibody levels were unavailable, preventing within-patient comparison over time. Heterogeneity in underlying renal pathology remains a potential confounder, as different disease entities may involve distinct mechanisms of T- and B-cell dysfunction. An additional methodological limitations is the potential for false-negative serology results, particularly for mumps IgG assays, which are known for lower analytical sensitivity and greater variability. Furthermore, measured IgG concentrations do not assess functional neutralising activity or cellular immune memory; therefore, it is possible that some patients may retain partial immune protection despite seronegativity.

In conclusion, our findings suggest that vaccine-induced antibody responses may decline in children with NS, even during remission. These findings highlight the clinical relevance of periodic assessment of vaccine-specific immunity and support individualised approaches to antibody monitoring, including consideration of booster vaccination in this vulnerable population.

Disclosures Ethics Committee Approval

This study was approved by the Ethics Committee of Tepecik Training and Research Hospital (2020/13-1).

Conflict of Interest

All authors declared that they have no conflict of interest.

Funding

There is no funding, grant or other source of support for this manuscript.

Authorship Contributions

Conception - S.A.Ç, Design – S.A.Ç, D.Y.; Supervision – F.M, B.K.D.; Materials – A.Ö., G.E, Ö.Ö.Ş; Data Collection and/or Processing – A.Ö, C.B. ,Ö.Ö.Ş; Analysis and/or Interpretation – S.A.Ç., D.A.; Literature Search – S.A.Ç., D.Y,G.E.R; Writing – S.A.Ç, A.Ö.; Critical Review – B.K.D.

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