The immunopathological processes underlying pediatric MCD arise from an imbalance among T-cell subsets, which is exacerbated by the age-dependent immaturity of immune regulatory circuits in children. Clinical data from multiple independent cohort studies have revealed a strong association between Treg-cell dysfunction and relapse risk in pediatric MCD [14]. In particular, a Japanese cohort study showed that, after steroid therapy, Treg-cell expansion was minimal in 128 patients with INS who had frequent relapses (24.8% increase from baseline) but substantial in patients without relapses (779.2% increase; P<0.001). Furthermore, a post-therapy Treg-cell increase of <400% presaged subsequent relapses with 94% sensitivity [4]. In a smaller European cohort (n=45), the sensitivity was slightly lower (89%), which may be attributable to differences in steroid dosing regimens and population-specific genetic backgrounds [14]; such differences would highlight the importance of population variability in pediatric MCD immune phenotypes.

This pediatric Treg-cell functional impairment stems primarily from overactivation of the mechanistic target of rapamycin complex 1 (mTORC1). Elevated levels of phosphorylated ribosomal protein S6, a downstream phosphorylation target of mTORC1 signaling, inhibit FOXP3 promoter activity via phosphorylation of signal transducer and activator of transcription 3, thereby directly impairing Treg-cell maturation and functional stability [11]. In pediatric Treg cells, the FOXP3 locus undergoes dynamic epigenetic maturation throughout childhood. Promoter methylation levels are higher and transcriptional stability is lower in preschool-aged children than in adolescents; thus, the Treg cells of young children are more vulnerable to mTORC1-mediated dysfunction. Beyond Treg-cell dysfunction, pediatric MCD is characterized by a marked imbalance in the Treg-cell/T-helper 17 (Th17)-cell axis. Active disease is associated with the expansion of proinflammatory Th17 cells, which secrete IL-17A to directly induce podocyte actin cytoskeletal injury; together with pre-existing Treg-cell functional impairment, this creates a self-reinforcing pathogenic cycle [15]. The heightened propensity for Th17 polarization in response to infectious triggers is unique to the developing pediatric immune system and may be a mechanistic link between common childhood infections and MCD relapses.

T-follicular helper (TFH) cells also exhibit stage-specific alterations in pediatric MCD. Upregulation of inducible T-cell co-stimulator is observed in new-onset cases, whereas elevation of OX40 levels predominates during relapses. This difference reflects a transition from acute immune initiation to persistent memory immune response [6]. In allergy-associated MCD, which is disproportionately prevalent among preschool-aged children, TFH cell–derived IL-4 drives B-cell immunoglobulin E production, providing a key mechanistic link between atopy and MCD flares in the pediatric population [16]. These T-cell subsets directly engage podocytes in a bidirectional pathogenic loop. Treg-cell dysfunction reduces cytotoxic T lymphocyte–associated protein 4-mediated suppression of podocyte CD80 expression, which triggers activation of the nucleotide-binding oligomerization domain (NOD)-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome and induces pyroptosis. Concurrently, TFH cell–derived IL-13 upregulates podocyte CD80 expression and initiates cytoskeletal damage mediated by Ras homolog family member A/Rho-associated coiled-coil-containing protein kinase (RhoA/ROCK) signaling. Thus, a vicious cycle of amplification of immune activation and podocyte injury is created [16,17]. Multiple independent clinical cohort studies have validated the correlation between circulating Treg-cell frequency and function and long-term prognosis in pediatric MCD, further supporting the central role of Treg-cell impairment in disease progression [18].

Extrafollicular B (EFOB) cell activation is a defining pediatric feature of MCD pathogenesis and is tightly coupled to the upstream T-cell dysregulation described previously. In humoral immunity, a key developmental distinction between children and adults is that children younger than 5 years rely heavily on EFOB-cell responses because germinal center formation and function remain immature during early life. This developmental trait accounts for why EFOB-cell activation plays a far more prominent role in pediatric MCD than in adult MCD. Clinicians have observed a significant correlation between elevated circulating EFOB-cell counts and cow’s milk protein allergy in pediatric patients with MCD, particularly among children younger than 5 years. These findings support targeted dietary interventions in this subgroup, but large-scale randomized controlled trials are still needed to confirm causality [19].

In a landmark 2023 study involving 96 pediatric patients with INS, investigators identified marked expansion of EFOB cells and enhanced signaling through the type I interferon/pro­liferation-inducing ligand (APRIL) pathway during active disease, wherein EFOB-cell activation is fully dependent on CD4+ T-cell help and closely associated with circulating levels of IL-13 and tumor necrosis factor alpha (TNF-α), which are key Th2/Th1 cytokines in MCD [2]. Pediatric podocytes express 1.8-fold higher levels of CD80 than adult podocytes and are therefore significantly more sensitive to EFOB cell–derived IL-13-mediated injury. This is a key pediatric mechanism that exacerbates the downstream pathological effects of EFOB-cell activation [8]. The well-documented efficacy of the B cell–depleting agent rituximab in pediatric MCD further supports the central role of B cells in disease pathogenesis. Colucci et al. [13] observed elevated memory B-cell counts in pediatric patients with frequently relapsing MCD and demonstrated that repeated rituximab administration prolonged the duration of pediatric remission from 10 to 16 months. This outcome significantly outperformed that reported in adults with MCD (median remission duration, 8 months) [13,18]. At the molecular level, EFOB cell–derived IL-13 activates the classical complement pathway, whereas anti-nephrin antibodies secreted by memory B cells bind directly to podocyte slit diaphragms. Together, these mechanisms generate a synergistic “antibody–complement injury” effect in which upstream immune dysregulation leads to downstream podocyte damage [8,20,21].

The discovery of anti-podocyte slit diaphragm autoantibodies has revolutionized the understanding of MCD immunopathogenesis. The striking pediatric predominance distinguishes childhood from adult disease: approximately 30% of children with MCD, compared with only 15% of adults, test positive for anti-nephrin antibodies [22,23]. These pathogenic autoantibodies serve as a direct molecular bridge between adaptive immune dysregulation and podocyte injury, acting as critical effector molecules of the driver layer. Ichikawa et al. [24] confirmed immunoglobulin G–nephrin colocalization in 84% of glomeruli from pediatric patients with MCD, a finding that is correlated directly with proteinuria severity and resolves completely with disease remission.

Data regarding the prevalence of anti-nephrin antibodies in pediatric cohorts have been inconsistent. Watts et al. [22] reported a 30% positivity rate in a North American cohort (n=87), whereas Hengel et al. [23], using optimized spatial immunofluorescence assays, detected antibodies in 42% of a European cohort (n=113). These discrepancies probably stem from differences both in detection methods (immunoprecipitation vs. high-resolution spatial imaging) and in disease activity status at the time of sampling; thus, standardized and age-appropriate detection assays are urgently needed for clinical use. Age-stratified analyses reveal that anti-nephrin antibody prevalence is as high as 47% among preschool-aged children (aged 3–6 years), compared with only 22% among adolescents aged 13–18 years. This finding mirrors the age-related gradient in relapse risk observed in clinical practice. In steroid-resistant pediatric cases, 48.5% of patients harbor anti-nephrin or anti-podocin antibodies. Moreover, second-line immunosuppressants, such as rituximab, are effective in 92.3% of these autoantibody-positive patients but in only 20% of antibody-negative patients [20]. The direct pathogenicity of these antibodies is further evidenced by animal studies, in which injection of purified anti-nephrin antibodies from pediatric patients with MCD induced massive proteinuria in nude mice [21]. At the molecular level, these autoantibodies trigger production of robust reactive oxygen species in podocytes, which directly induces ferroptosis and activates the NLRP3 inflammasome to drive pyroptosis; thus, they are central mediators linking systemic autoimmunity to podocyte death in pediatric MCD [21,25].

NLRP3-mediated pyroptosis, a proinflammatory form of programmed cell death, plays a disproportionately prominent role in pediatric MCD because pediatric podocytes exhibit higher basal NLRP3 expression and greater sensitivity to oxidative stress than adult podocytes [9]. A 2024 study of 26 pediatric patients with MCD revealed significantly reduced podocyte density (9.75±0.66 vs. 17.96±0.83 in healthy controls) and elevated urinary levels of IL-18, a key downstream effector of pyroptosis; however, the strength of these findings is limited by the small sample size and lack of age-stratified analyses [9]. The underlying signaling cascade involves upregulated CD36-mediating oxidized low-density lipoprotein (ox-LDL) influx, which in turn activates the NLRP3/gasdermin D pathway to trigger pyroptotic cell death [9].

Standard steroid therapy reduces circulating ox-LDL and urinary IL-18 levels but fails to inhibit upstream CD36/NLRP3 activation in podocytes, which suggests that steroids target only the downstream inflammatory effects of pyroptosis. This limitation is a critical drawback for pediatric mechanism–targeted therapies. Pyroptosis participates in bidirectional crosstalk with the upstream driver layer. IL-18 released during pyroptosis upregulates transferrin receptor (TFRC) to expand podocyte iron pools (which exacerbates ferroptosis) and promotes IL-13 secretion by EFOB cells; this results in cyclic exacerbation of immune dysregulation and podocyte injury [9,25]. Moreover, C5a, a key complement-derived fragment, activates NLRP3 signaling via the podocyte C5aR, integrating complement signaling into this pathogenic loop [26]. Urinary levels of cleaved gasdermin D and IL-18 are promising biomarkers of pyroptotic activity in pediatric MCD that can be measured noninvasively. Their levels strongly correspond to disease activity and decline rapidly with treatment-induced remission.

Although adaptive immunity remains the core focus of research on MCD pathogenesis, accumulating evidence indicates that innate immune cells are key modulators of the pediatric MCD disease network, encompassing environmental triggers, adaptive immune activation, and podocyte injury. Because of the developmental immaturity of the innate immune system, which remains highly responsive to microbial and inflammatory stimuli throughout early childhood, the role of innate immune cells is disproportionately prominent in children.

Circulating levels of nonclassical CD16⁺ monocytes are elevated in the peripheral blood of pediatric patients with INS during active disease and normalize after disease remission [27]. These activated monocytes secrete high levels of proinflammatory cytokines including TNF-α and IL-1β, which contribute to the initiation and recurrence of minimal change nephrotic syndrome by inducing glomerular injury and proteinuria [28]. The M1/M2 polarization balance of renal-infiltrating macrophages is developmentally regulated in children. Younger children exhibit a greater propensity for proinflammatory M1 macrophage polarization in response to infectious stimuli, which further exacerbates glomerular injury. In pediatric MCD, viral or bacterial triggers activate plasmacytoid dendritic cells, which then produce large amounts of type I interferon that drive EFOB-cell activation and autoantibody production [2]. The heightened type I interferon response to viral stimuli in preschool-aged children provides a mechanistic explanation for the high rate of infection-triggered relapses observed in this age group. Type 2 innate lymphoid cells, activated by epithelium-derived cytokines (IL-25 and IL-33) in the context of allergy or infection, secrete large amounts of IL-13 and IL-4, which directly drive podocyte CD80 expression and cytoskeletal damage and promote B-cell production of immunoglobulin E [29]. The high level of activity of these lymphoid cells in early life is considered a key driver of the high incidence of allergy-associated MCD among preschool-aged children. Importantly, innate immune cells function not only as upstream drivers of adaptive immune dysregulation but also as direct responders to podocyte injury signals, forming a bidirectional crosstalk between the driver and execution layer of the disease network (Fig. 2).

Integrin β1 (ITGB1) is the key adhesion molecule responsible for anchoring podocytes to the glomerular basement membrane (GBM), and its aberrant cytoplasmic localization—observed in 16.8% of adult podocytopathies—compromises podocyte–GBM adhesion in pediatric MCD and directly underpins podocyte foot process fusion and podocyte detachment [30]. ITGB1 expression in podocytes is developmentally regulated. Podocyte expression is notably reduced in children younger than 3 years compared with adolescents. Consequently, podocytes in young children are inherently more vulnerable to adhesion defects and detachment. High glucose and IL-13 levels activate the urokinase-type plasminogen activator receptor/plasminogen activator inhibitor-1 pathway linked to ITGB1 endocytosis in animal models; however, its role in human pediatric MCD remains incompletely understood. In a small pilot study (n=12), researchers failed to detect overexpression of urokinase-type plasminogen activator receptor in pediatric MCD kidney biopsy samples, in contrast to adult samples [31]. This finding further highlights key age-related differences in the mechanisms underlying podocyte adhesion defects.

Reduced podocyte–GBM adhesion activates multiple stress-response pathways. Integrin β5 (ITGB5)/focal adhesion kinase pathway activation drives pyroptosis, whereas acyl-coenzyme A synthetase long-chain family member 4 (ACSL4)-linked ferroptosis represents another critical injury mechanism triggered by adhesion loss [25,32]. The interplay between these pathways in pediatric podocytes must be explored further because current data are extrapolated largely from adult or animal models. The pediatric-specific expression patterns of ITGB subunits (e.g., ITGB1 and ITGB5) across different age groups remain uncharacterized.

The actin cytoskeleton is the core of podocyte structure and filtration function, and its dysregulation is a universal hallmark of podocytopathies [33]. In pediatric MCD, TFH cell–derived IL-13 mediates cytoskeletal disorganization in podocytes by downregulating synaptopodin and α-actinin-4, two key actin-stabilizing proteins, while simultaneously activating RhoA/ROCK signaling to promote actin depolymerization [7,17]. Synaptopodin expression in podocytes increases progressively with age. As preschool-aged children (aged 3–6 years) have considerably lower levels than older patients, their podocyte cytoskeletons are inherently less stable and more sensitive to inflammatory injury. The RhoA/ROCK signaling pathway is more sensitive in preschool-aged children than in older children, although this assertion awaits validation in age-stratified clinical studies.

Histone deacetylase 6 (HDAC6) overactivation further contributes to cytoskeletal dysfunction in pediatric MCD through deacetylation of α-tubulin, disruption of microtubule stability, and impairment of autophagic flux in podocytes [34]. HDAC6 may synergize with RhoA/ROCK signaling to exacerbate podocyte injury, but this interaction remains unconfirmed in primary human podocytes. HDAC6 inhibitors (e.g., tubastatin A) have shown promise in preclinical studies, but rigorous validation in pediatric cohorts is needed. In addition, because HDAC6 plays critical roles in neuronal development, its use in children younger than 5 years old raises safety concerns about toxicity [34].

Hyperactivation of mTORC1 is a key component of podocyte injury in pediatric MCD, driven primarily by reduced expression of DNA repair enzymes in developing podocytes, which leads to increased DNA damage and subsequent mTORC1 activation [5]. Preclinical studies have shown that rapamycin, an mTORC1 inhibitor, improves podocyte health and reduces DNA damage in Ercc1-knockout mice. However, it fails to reduce established proteinuria, indicating that mTORC1 inhibition alone is insufficient to reverse advanced podocyte injury [5]. Such a cross-module signaling molecule integrates both immune and podocyte pathogenic pathways: mTORC1 inhibits Treg-cell differentiation in the driver layer, and TFRC is upregulated to promote podocyte ferroptosis in the execution layer. In this way, the entire pathogenic network is reinforced [8,11,25]. During kidney development, mTORC1 plays a critical physiological role in regulating podocyte growth and maturation, and its dysregulation in children thus not only causes acute injury but also disrupts normal podocyte developmental programming, a mechanism unique to the pediatric population.

Ferroptosis, an iron-dependent form of regulated cell death driven by lethal lipid peroxidation, is pathogenic in children, resulting from the immaturity of systemic iron metabolism and the developmental characteristics of pediatric podocytes. The core regulatory axis of ferroptosis comprises TFRC-mediated iron overload, ACSL4-mediated lipid peroxidation, and glutathione peroxidase 4/solute carrier family 7 member 11 (GPX4/SLC7A11)-mediated antioxidant defense. This axis has been well characterized in podocyte injury across multiple glomerular diseases [25]. In the context of MCD, in vitro studies have confirmed that IL-13 and complement C5b-9 can trigger ferroptosis in podocytes by inhibiting SLC7A11 activity, a key component of the system Xc^– cystine/glutamate antiporter [24,26].

Children, particularly preschool-aged children, are vulnerable to ferroptosis because of developmental factors. Rapid growth increases intestinal iron absorption, which causes systemic iron availability to increase, and immature podocytes express higher levels of TFRC and have weaker antioxidant capacity than do mature adult podocytes. Oxidative stress, which is more severe in active pediatric MCD, inhibits nuclear factor erythroid 2-related factor 2, a transcription factor, downregulating its downstream targets heme oxygenase-1 and GPX4 to further promote ferroptosis [35,36]. Cross-activation between ferroptosis and pyroptosis creates a self-reinforcing vicious cycle of podocyte injury. Lipid peroxides derived from ferroptosis activate the NLRP3 inflammasome to drive pyroptosis, whereas complement C5b-9 inhibits SLC7A11 to exacerbate ferroptosis [24-26]. This mutually reinforcing pathogenic network highlights the need for multitarget therapeutic strategies in pediatric MCD, as inhibition of a single pathway may be insufficient to disrupt the vicious cycle of podocyte injury and death.

Barry et al. [12] identified the rs412175 variation in the NPHS1 gene (odds ratio, 1.65) and the HLA-DQA1 haplotype (odds ratio, 3.56) as significant risk factors for pediatric SSNS. These alleles are more common among children of European ancestry than among Asian children. The effect of the HLA-DQA1 haplotype is strongest among preschool-aged children and diminishes with age, mirroring the age-related decline in MCD incidence and relapse risk. Of the patients with pediatric SRNS, 24.7% carry monogenic pathogenic variants, most commonly COL4A5 (11.2%) and NPHS2 (5.6%), which are associated with a 9.1% immune therapy response rate and 10-fold higher risk for CKD, as detailed in section 4 [10,11]. Routine genetic testing for pediatric SRNS-MCD is increasingly recommended in international guidelines. To guide global implementation, cost-effectiveness analyses are needed in low-resource settings.

Epidemiological studies have identified a 1.5–2 times higher incidence of childhood INS in boys than in girls, particularly among children younger than 10 years of age [1,3]. These sex differences likely result from multiple interacting factors. Sex hormones modulate immune cell function even in prepubertal development, X chromosome-linked genes such as COL4A5 directly influence sex differences in genetic susceptibility, and sex-related differences in drug metabolism affect treatment responses in boys and girls [10,39,40]. However, the molecular mechanisms underlying these sex-specific differences remain poorly understood, and sex should be incorporated as a biological variable in future studies to facilitate the development of truly individualized precision therapies.

Downregulation of Krüppel-like factor 4 (KLF4), a key podocyte transcription factor, is correlated with nephrin promoter hypermethylation, a critical epigenetic mechanism in pediatric MCD [41]. KLF4 maintains nephrin promoter accessibility, and its reduction causes DNA methyltransferase 1 (DNMT1) to be added to methylate CpG islands, which inhibits nephrin transcription [37,41]. Renin–angiotensin–aldosterone system (RAAS) activation suppresses KLF4 activity, whereas RAAS inhibitors exert an epigenetic memory effect by restoring KLF4 expression and reversing these repressive epigenetic markers. This suggests that epigenetic-based therapies have potential for treating pediatric MCD [37]. Podocyte epigenome is highly plastic during kidney development. Dynamic DNA methylation patterns are more susceptible to environmental modulation (e.g., infection, diet, and drug exposure) in children than in adults. Serum levels of members of the miR-30 family and urinary levels of miR-30a-5p fluctuate with disease activity in pediatric MCD; thus, they have potential as biomarkers of disease activity that can be measured noninvasively [42].

Since 2015, research on the pathogenesis of childhood MCD has been reconceptualized. The long-standing “single T-cell defect” theory has been replaced by a coordinated T-cell/B-cell dysregulation model that has been validated in multicenter pediatric clinical cohort studies. The core pathogenic elements of this model include Treg-cell functional immaturity, activation of the TFH-cell/EFOB-cell axis, and the development of anti-nephrin autoantibodies. These discoveries have provided clear, actionable targets for B cell–targeted immunotherapies in children. These mechanistic insights have helped identify multiple actionable therapeutic targets across the three-layer pathogenic network (Table 2). In addition, several key emerging mechanistic insights with promising preclinical and preliminary pediatric clinical evidence have reshaped clinicians’ understanding of the disease. First, pyroptosis and ferroptosis, with mutual reinforcement via the IL-18–TFRC axis and the C5b-9–SLC7A11 axis, are key execution pathways of podocyte injury in pediatric MCD. Second, genetic susceptibility (presence of HLA-DQA1 or COL4A5), epigenetic regulation (KLF4–DNMT1 axis), and the gut–kidney axis (butyrate–HDAC–FOXP3 pathway) are key modulators of the disease network. The entire pathogenic network is inherently governed by pediatric development. The immaturity of the immune system and the biological characteristics of developing podocytes profoundly shape disease manifestations, treatment responsiveness, and long-term outcomes in childhood MCD.

In future research, investigators should prioritize three core directions: (1) resolving inconsistencies in anti-nephrin antibody prevalence through the development of standardized detection assays and age-stratified multicenter pediatric studies; (2) validating multimodal biomarker panels integrating immune, epigenetic, and urinary podocyte injury markers to distinguish SSNS, SRNS, and frequent relapsing INS across different pediatric age groups; and (3) developing pediatric-specific targeted therapies, prioritizing agents with minimal effects on growth and immune development. In summary, clinicians’ understanding of MCD has evolved from a simplistic single-link dysregulation model to a sophisticated, multilayered pathogenic network. Future interdisciplinary research integrating developmental biology, immunology, and epigenetics will advance treatment beyond symptom control to mechanism-based cures for children affected by this disease.