Synbiotic Combination of Lactococcus lactis LB1022 and Fructo-Oligosaccharides Mitigates the Atopic March by Modulating the Microbiota-Gut–Skin–Lung Axis

TL;DR

A synbiotic combining Lactococcus lactis LB1022 and fructo-oligosaccharides reduces allergic skin and lung inflammation in mice by modulating gut and immune health.

Contribution

This study introduces a novel synbiotic formulation that effectively mitigates the progression of allergic diseases via microbiota modulation.

Findings

The synbiotic reduced skin pathology and airway inflammation in a murine model of allergic disease.

Synbiotic treatment enriched SCFA-producing bacteria and lowered Th2 cytokine responses.

The formulation showed protective effects through modulation of the gut-skin-lung axis.

Abstract

Dysregulated gut microbiota is increasingly recognized as a major contributor to allergic diseases and their progression. A key clinical manifestation of this progression is the atopic march, in which atopic dermatitis (AD) precedes the development of allergic airway disease. Although prebiotics and probiotics individually improve AD symptoms, their combined use as synbiotics, especially with regard to preventing the progression from cutaneous inflammation to airway hypersensitivity, has not been clearly established. In this study, we assessed the biological activity of a synbiotic composed of fructo-oligosaccharides (FOS) and Lactococcus lactis LB1022 in an ovalbumin (OVA)-induced murine model of AD and asthma-like inflammation. Female BALB/c mice were treated for eight weeks with FOS, L. lactis LB1022, or their combination following OVA sensitization. The synbiotic formulation produced the strongest protective effects, markedly reducing AD-like skin pathology, suppressing airway inflammatory cell influx, and lowering Th2-skewed cytokine responses. These protective effects were further supported by significant reductions in serum IgE and Th2-associated IgG1 levels. Synbiotic treatment also enriched multiple short-chain fatty acid (SCFA)-producing taxa, including Lactobacillus and Bifidobacterium species, resulting in increased fecal SCFA concentrations that were closely associated with improvements in systemic and mucosal immunity. These results demonstrate that the FOS–L. lactis LB1022 synbiotic mitigates both epidermal and respiratory allergic inflammation through coordinated regulation of the microbiota-gut–skin–lung axis. The findings highlight a promising dietary approach for reducing the risk of progression along the atopic march and address an important gap in current allergy-related microbiome research.

Figures

C](#F1)). These microbial families include taxa known to contribute to short-chain fatty acid (SCFA) production and immune homeostasis. Consistent with these family-level shifts, OTU-level analysis revealed enrichment of taxa belonging to the genera *Bacteroides*, *Lactobacillus*, *Bifidobacterium*, and *Prevotella* in the synbiotic group ([Fig. 1D](#F1)), suggesting a microbial composition functionally linked to enhanced SCFA availability and improved host physiological responses observed in subsequent analyses.

A](#F2)). Correlation analysis revealed that several SCFA-producing species including *Bacteroides acidifaciens*, *Bifidobacterium pseudolongum*, *Lactobacillus crispatus*, *Limosilactobacillus reuteri*, and *Roseburia intestinalis* were positively associated with increased SCFA concentrations (*p* < 0.01) ([Fig. 2B](#F2)). Conversely, *Ruminococcus gnavus*, a taxon frequently linked to gut inflammation and atopic conditions, showed negative correlations with propionate and butyrate levels (*p* < 0.01). These findings demonstrate that synbiotic supplementation not only improved microbial compo

F](#F3)). Specifically, IL-4 and IL-13 mRNA levels in the synbiotic group were reduced to approximately 40% of those observed in the OVA control group (*p* < 0.001). IL-10 expression decreased across all supplemented groups, consistent with reduced inflammatory burden and immune activation.

C](#F4)), indicating attenuation of allergic and inflammatory immune activation. The downregulation of both Th2 and Th17 pathways highlights the capacity of synbiotics to rebalance mucosal immunity and reduce susceptibility to downstream airway inflammation.

A](#F5)). IgG1, an indicator of Th2-biased responses, was likewise reduced ([Fig. 5B](#F5)). Interestingly, IgG2a levels were selectively reduced in the synbiotic group, suggesting broader immunomodulatory activity compared with probiotic supplementation alone ([Fig. 5C](#F5)). These data confirm that synbiotic supplementation alleviates systemic Th2-driven inflammation and improves immune balance in OVA-sensitized mice.

C](#F6)). Levels of IL-33 and TARC—key mediators of Th2 cell recruitment and activation—were also lower in lung tissue and serum (Fig. S2). Histological assessment revealed that synbiotic supplementation reduced general inflammatory infiltration around the airways ([Fig. 6D](#F6) and [6E](#F6)). PAS staining demonstrated attenuation of mucus hypersecretion and goblet cell hyperplasia in the synbiotic group, whereas the OVA control group exhibited extensive remodeling characteristic of asthma-like pathology ([Fig. 6F](#F6)). Together, these findings show that synbiotic supplementation effective

Full text

Introduction

The global incidence of allergic diseases, including atopic dermatitis (AD), asthma, and allergic rhinitis, has increased markedly over recent decades [1, 2]. AD often presents early in life and is widely regarded as the initiating step of the atopic march, a clinical trajectory in which cutaneous inflammation precedes the onset of chronic respiratory allergic disorders [3]. Although the mechanisms that drive this progression remain to be fully clarified, immune imbalance, impairment of epithelial barriers, and compositional changes in the gut microbiota are consistently implicated as central contributing factors [4]. Furthermore, individuals with allergic conditions frequently display heightened susceptibility to metabolic disturbances, emphasizing the importance of early preventive strategies [5].

The gut microbiota has emerged as a key regulator of immune development, mucosal barrier function, and microbial metabolite production [6]. Patients with AD and asthma often exhibit reduced microbial diversity together with decreased levels of beneficial genera, including Bifidobacterium and Lactobacillus [7-9]. These findings have motivated research into dietary interventions that modify the gut ecosystem as a means of controlling allergic inflammation [10, 11].

Probiotics such as Lactobacillus and Lactococcus strains are reported to alleviate AD symptoms by modulating Th1/Th2 immunity and reshaping the gut microbial community [12-15]. Prebiotics promote the growth of beneficial taxa and mitigate allergen-induced inflammation. Typical prebiotics such as fructo-oligosaccharides (FOSs) have been reported to ameliorate dust mite-induced airway inflammation [16]. However, prebiotics have predominantly focused on the host without a comprehensive analysis of changes in the gut microbiota composition.

Synbiotics, which combine probiotics with their complementary prebiotic substrates, offer the potential for additive or synergistic benefits [17]. However, their impact on halting the transition from AD to asthma-like disease has not been comprehensively evaluated, and the crosstalk among the gut, skin, and airway compartments requires deeper mechanistic understanding.

Lactococcus lactis LB1022 has previously been shown to exhibit anti-allergic and immunomodulatory activities in both in vitro systems and an OVA-induced atopic dermatitis mouse model [18]. Likewise, FOS, including kestose-enriched formulations, has been reported to alleviate AD by promoting short-chain fatty acid (SCFA)-producing microbes and modulating gut–immune interactions [19]. Building on these findings, combining L. lactis LB1022 with FOS may provide enhanced and complementary protection against the progression of the atopic march.

The objectives of this study were twofold: (i) to assess the efficacy of FOS, L. lactis LB1022, and their synbiotic combination in ameliorating AD-like skin lesions and preventing asthma-like airway inflammation in OVA-sensitized mice, and (ii) to determine how synbiotic treatment influences the gut microbiota and SCFA production in relation to immune modulation. Through these analyses, we provide evidence that synbiotics may serve as a practical dietary approach to limit the progression of allergic diseases.

Materials and Methods

Preparation of Synbiotic, Probiotic, and Prebiotic Formulations

L. lactis LB1022, originally isolated from cheese, was maintained in our laboratory culture collection. Fructo-oligosaccharides (FOS; purity > 98%) were obtained from the Food R&D Center of Samyang Corporation (Republic of Korea). For preparation of the probiotic suspension, L. lactis LB1022 was streaked onto tryptic soy agar (TSA; BD, USA) and incubated aerobically for 16 h at 30°C using an MIR-253 incubator (Sanyo, Japan). Bacterial cells were harvested by centrifugation (8,000 ×g, 20 min, 4°C), washed twice with sterile phosphate-buffered saline (PBS), and resuspended in PBS. Fresh bacterial suspensions were prepared weekly and stored at −20°C to maintain short-term stability. Prior to oral gavage, aliquots were thawed on ice, and viable cell counts were verified by plate counting on TSA. Colony-forming units (CFUs) were confirmed at the time of preparation and periodically during the storage period, and suspensions were adjusted as necessary to ensure a consistent daily dose of 1 × 10^8^ CFU/200 μl per mouse. The probiotic suspension and FOS solution were mixed immediately before administration to minimize potential loss of bacterial viability and to ensure dosing consistency.

Animal Experimental Design

Female BALB/c mice (5 weeks old, 18–20 g; n = 30) were purchased from Central Lab Animal Inc. (Republic of Korea). After a 1-week acclimation period, animals were housed under a 12 h light/12 h dark cycle with free access to chow and water. All procedures adhered to the guidelines of the Korean Ministry of Food and Drug Safety and were approved by the Institutional Animal Care and Use Committee of Chung-Ang University (IACUC No. 2018-00022).

To induce AD-like inflammation, dorsal skin was shaved weekly, and mice received intraperitoneal injections of ovalbumin (OVA; 50 μg) mixed with alum at weeks 1, 3, 5, and 7. At week 15, airway challenge was performed by intranasal administration of OVA (50 μg/day) for four consecutive days (Fig. S1). At week 16, skin assessments, bronchoalveolar lavage fluid (BALF), blood, tissue samples (skin, ileum, lung), and fecal pellets were collected.

Details of the experimental diet are provided in the Supplementary Material. Prebiotics, probiotics, or synbiotics (in 200 μl of sterilized water) were orally administered daily (by gavage) until the 16th week as follows: probiotic group (Pro) – L. lactis LB1022 was administered at 10^8^ CFU/day; prebiotic group (Pre) – FOS was administered at 3.7 mg/day, and synbiotic group (Syn) was administered a combined dose of the prebiotic and probiotic. The unsupplemented control OVA-sensitized group was treated with an equal volume of PBS (200 μl) daily.

Assessment of AD-Like Skin Symptoms

AD-like dermatitis severity was evaluated twice weekly. Four parameters, including erythema, edema, dryness, and excoriation, were scored individually on a 0–3 scale (0, none; 3, severe). The cumulative dermatitis score was used as an index of skin inflammation.

RNA Extraction and Quantitative Real-Time PCR

Skin, ileum, and lung tissues were homogenized, and total RNA was isolated using the RNeasy Mini Kit (Qiagen, Germany). DNase-treated RNA was reverse-transcribed into cDNA and analyzed using quantitative real-time PCR (RT-qPCR). Primer sequences are listed in Table S1. Gene expression was normalized to housekeeping genes and quantified using the ^ΔΔ^Ct method.

Measurement of Serum Cytokines and Immunoglobulins

Blood was collected and allowed to clot at 4°C for 1 h, followed by centrifugation (5,000 ×g, 1 h). Serum concentrations of IgE, IgG1, IgG2a, IL-4, IL-5, IL-12, IL-13, IL-33, IL-1β, TARC, and eotaxins were determined using ELISA kits (R&D Systems, USA; Abcam, UK) according to manufacturer protocols.

Histological Examination

Skin, ileum, and lung tissues were fixed in 10% neutral-buffered formalin for 48 h, embedded in paraffin, and cut into 4–5 μm sections. Sections were stained with hematoxylin and eosin (H&E) for inflammation, toluidine blue for mast cells, and periodic acid–Schiff (PAS) for mucus production [20]. Images were captured using a DM4000 B microscope (Leica Microsystems, Germany).

Bronchoalveolar Lavage Fluid (BALF) Analysis

Following tracheal cannulation, lungs were lavaged twice with 1 ml PBS. Total BALF cells were counted using a TC20 automated counter (Bio-Rad, USA). Cytospin slides were stained with Wright–Giemsa, and 500 cells per slide were classified into macrophages, eosinophils, neutrophils, and lymphocytes. Airway inflammation scores were calculated according to established criteria.

Short-Chain Fatty Acid (SCFA) Quantification

Fecal short-chain fatty acid levels were determined by high-performance liquid chromatography (HPLC) using an Ultimate 3000 system (Thermo Dionex, USA). Fecal pellets were suspended in distilled water, homogenized, and centrifuged at 8,000 ×g for 15 min at 4°C. The resulting supernatants were collected and purified using Sep-Pak C18 cartridges (Waters Corp., USA). Acetate, propionate, butyrate, and lactate were separated on an Aminex HPX-87H column (300 × 10 mm; Bio-Rad, USA) using 0.01 N sulfuric acid as the mobile phase at a flow rate of 0.5 ml/min under isocratic conditions. SCFA peaks were detected using a refractive index detector (RefractoMAX520; ERC, Japan).

Gut Microbiome Analysis

Genomic DNA was extracted from fecal samples using the FastDNA SPIN Kit (MP Biomedicals, USA). The V3–V4 regions of the 16S rRNA gene were amplified with primers 341F/805R and sequenced on an Illumina MiSeq platform (Macrogen Inc., Republic of Korea). Reads were processed in QIIME2, clustered into operational taxonomic units (OTUs) at 97% similarity, and annotated using the SILVA reference database. For the diversity analysis, the phyloseq, DESeq2, and microbiome packages in R [21-23] were used, and visualization of the plots was done using the ggplot2 package [24] in R. Group differences were evaluated using PERMANOVA (vegan package). Sequencing data were submitted to the NCBI SRA under accession numbers SRR17901942–SRR17901971.

Statistical Analysis

Statistical analyses were conducted using GraphPad Prism 8 (GraphPad Software, USA). Data are presented as mean ± SEM. Group comparisons were performed using one-way ANOVA with Tukey’s post-hoc test or the Kruskal–Wallis test with Dunn’s correction. Differences were considered statistically significant at p < 0.05.

Results

Synbiotic Supplementation Modulated Gut Microbial Communities and Enhanced SCFA Production

A total of 2,406,815 high-quality paired-end reads were obtained from 30 fecal samples, with an average of 41,973 ± 404.8 reads per mouse. Principal coordinate analysis based on Bray–Curtis dissimilarity revealed clear separation among the experimental groups, indicating distinct microbial community compositions following dietary intervention (PERMANOVA, R^2^ = 0.5684, p = 0.001) (Fig. 1A). OVA sensitization markedly reduced microbial richness and phylogenetic diversity, whereas mice receiving synbiotic supplementation displayed a significant restoration of Faith’s phylogenetic diversity compared with the OVA control group (p < 0.01) (Fig. 1B). Although Shannon’s diversity index did not differ significantly among groups, synbiotic-treated mice exhibited a community structure clearly distinct from both the OVA control and single-component supplementation groups.

At the taxonomic level, the synbiotic group exhibited reduced relative abundances of Firmicutes families commonly associated with gut dysbiosis, including Lachnospiraceae and Ruminococcaceae, while showing increased abundances of Bacteroidaceae, Lactobacillaceae, Prevotellaceae, and Bifidobacteriaceae (Fig. 1C). These microbial families include taxa known to contribute to short-chain fatty acid (SCFA) production and immune homeostasis. Consistent with these family-level shifts, OTU-level analysis revealed enrichment of taxa belonging to the genera Bacteroides, Lactobacillus, Bifidobacterium, and Prevotella in the synbiotic group (Fig. 1D), suggesting a microbial composition functionally linked to enhanced SCFA availability and improved host physiological responses observed in subsequent analyses.

To assess metabolic consequences of these compositional changes, SCFA levels were evaluated. Principal coordinate analysis of SCFA profiles showed clear gradients associated with synbiotic treatment, including increased butyrate (R^2^ = 0.1233, p = 0.001), propionate (R^2^ = 0.111, p = 0.002), lactate (R^2^ = 0.179, p = 0.001), and acetate (R^2^ = 0.085, p = 0.018) (Fig. 2A). Correlation analysis revealed that several SCFA-producing species including Bacteroides acidifaciens, Bifidobacterium pseudolongum, Lactobacillus crispatus, Limosilactobacillus reuteri, and Roseburia intestinalis were positively associated with increased SCFA concentrations (p < 0.01) (Fig. 2B). Conversely, Ruminococcus gnavus, a taxon frequently linked to gut inflammation and atopic conditions, showed negative correlations with propionate and butyrate levels (p < 0.01). These findings demonstrate that synbiotic supplementation not only improved microbial composition but also enhanced metabolic output associated with immune regulation.

Synbiotic Supplementation Ameliorated AD-Like Skin Lesions and Reduced Cutaneous Immune Activation

OVA-sensitized mice developed pronounced AD-like skin inflammation characterized by erythema, edema, dryness, and excoriation. Synbiotic-treated mice showed a marked reduction in visible dermatitis severity, reflected by diminished cumulative skin scores compared with the OVA control group (Fig. 3A and 3B). Histological examination revealed substantial reductions in epidermal hyperplasia and dermal thickening in both the probiotic and synbiotic groups; however, the improvement was most pronounced in synbiotic-treated mice (Fig. 3C and 3D).

Toluidine blue staining demonstrated that mast cell accumulation, a hallmark of allergic skin inflammation, was significantly reduced in the probiotic and synbiotic groups (Fig. 3E). Eosinophil infiltration followed the same trend. Prebiotic supplementation alone produced milder improvements but did not fully suppress inflammatory cell recruitment.

RT-qPCR analysis showed that OVA sensitization strongly induced expression of Th2-associated cytokines (IL-4, IL-13), Th17 cytokines (IL-17), and epithelial alarmins (IL-33, TSLP). Synbiotic supplementation significantly downregulated IL-4, IL-13, IL-17, and IL-33, indicating broad attenuation of Th2/Th17-dominated inflammation (Fig. 3F). Specifically, IL-4 and IL-13 mRNA levels in the synbiotic group were reduced to approximately 40% of those observed in the OVA control group (p < 0.001). IL-10 expression decreased across all supplemented groups, consistent with reduced inflammatory burden and immune activation.

Together, these results demonstrate that the synbiotic formulation exerts potent protective effects against AD-like skin inflammation through suppression of cytokine expression and inflammatory cell infiltration.

Synbiotic Treatment Improved Gut Mucosal Immune Responses and Reduced Ileal Inflammation

To determine whether synbiotic supplementation modulates mucosal immunity beyond the skin, ileal tissues were examined. Mast cell infiltration into the ileal mucosa was significantly reduced in the probiotic and synbiotic groups (Fig. 4A and 4B). Consistent with these histological findings, synbiotic administration regulated cytokine expression associated with Th1, Th2, Th17, and epithelial alarmin signaling.

Specifically, IL-12 (Th1-associated cytokine) expression increased in both the probiotic and synbiotic groups, suggesting a shift toward a more balanced immune profile under allergic conditions. In contrast, synbiotic-treated mice exhibited marked reductions in IL-4, IL-5, and IL-13 (Th2-associated cytokines), as well as IL-17 and TSLP (Fig. 4C), indicating attenuation of allergic and inflammatory immune activation. The downregulation of both Th2 and Th17 pathways highlights the capacity of synbiotics to rebalance mucosal immunity and reduce susceptibility to downstream airway inflammation.

Collectively, the ileal data support a model in which synbiotic supplementation modulates both epithelial alarmins and T-cell–associated cytokine networks, thereby stabilizing mucosal immune homeostasis.

Synbiotic Supplementation Modified Serum Cytokine Patterns and Immunoglobulin Profiles

Systemic cytokine patterns reflected the protective effects observed in local tissues. Compared with the OVA control group, synbiotic-treated mice displayed significantly reduced Th2-associated cytokines (IL-4, IL-5, IL-13), accompanied by an elevation in IL-12. Treg-associated cytokines IL-10 and IL-1β were also reduced following synbiotic supplementation.

Serum IgE levels, which are tightly linked to mast cell activation and allergic sensitization, were markedly decreased in both the probiotic and synbiotic groups, with the latter showing the strongest suppression (Fig. 5A). IgG1, an indicator of Th2-biased responses, was likewise reduced (Fig. 5B). Interestingly, IgG2a levels were selectively reduced in the synbiotic group, suggesting broader immunomodulatory activity compared with probiotic supplementation alone (Fig. 5C). These data confirm that synbiotic supplementation alleviates systemic Th2-driven inflammation and improves immune balance in OVA-sensitized mice.

Synbiotic Supplementation Suppressed Asthma-Like Airway Inflammation and Reduced Th2 Cytokine Expression in the Lung

OVA-challenged mice exhibited typical asthma-like features, including elevated inflammatory cells in BALF and increased Th2 cytokines in lung tissue. Synbiotic treatment markedly reduced total BALF cellularity, whereas the prebiotic group did not show significant improvement (Fig. 6A). Reductions in eosinophils, macrophages, neutrophils, and lymphocytes were evident in both the probiotic and synbiotic groups (Fig. 6B).

Correspondingly, lung mRNA expression levels of IL-4, IL-5, IL-13, IL-17, and TSLP were significantly downregulated in synbiotic-treated mice (Fig. 6C). Levels of IL-33 and TARC—key mediators of Th2 cell recruitment and activation—were also lower in lung tissue and serum (Fig. S2). Histological assessment revealed that synbiotic supplementation reduced general inflammatory infiltration around the airways (Fig. 6D and 6E). PAS staining demonstrated attenuation of mucus hypersecretion and goblet cell hyperplasia in the synbiotic group, whereas the OVA control group exhibited extensive remodeling characteristic of asthma-like pathology (Fig. 6F). Together, these findings show that synbiotic supplementation effectively suppresses airway inflammation and mitigates pathological features associated with asthma-like responses.

Discussion

This study investigated whether dietary supplementation with a prebiotic (FOS), a probiotic (L. lactis LB1022), or their combined synbiotic formulation could influence the progression of AD toward asthma-like airway inflammation in an OVA-induced mouse model. Although previous work has shown that certain synbiotics can modulate gut microbiota and attenuate allergic responses [17, 25], formulations combining L. lactis with FOS have not been extensively explored, particularly in the context of preventing the atopic march. In addition, unlike well-characterized L. lactis strains that are primarily utilized as dairy starter cultures, LB1022 may possess distinct metabolic features that support its adaptability to dietary oligosaccharides and functional compatibility with FOS. Such strain-level characteristics may contribute to more efficient SCFA production and downstream immunomodulatory effects when combined with FOS, supporting the concept of strain–substrate specificity as an important consideration in synbiotic formulation and design. In the present study, the synbiotic consistently produced stronger protective effects than either component alone, indicating a synergistic interaction between FOS and L. lactis LB1022.

This synergy is mechanistically defined by FOS enhancing the metabolic activity and gut-level efficacy of L. lactis LB1022, as well as other beneficial gut commensals, thereby promoting increased production of SCFAs, including acetate, propionate, and butyrate. Elevated SCFA levels may contribute to systemic immune regulation by influencing immune cell differentiation and function, which is consistent with the observed attenuation of Th2- and Th17-associated cytokine responses and the downregulation of epithelial-derived alarmins, including thymic stromal lymphopoietin (TSLP) and interleukin-33 (IL-33), across the gut, skin, and lung tissues [26]. Collectively, this coordinated immunological modulation provides a key mechanistic basis for the attenuation of atopic dermatitis pathology and the mitigation of atopic march progression toward allergic airway inflammation.

Dysbiosis of the gut microbiota is widely recognized as a contributing factor in allergic diseases, including atopic dermatitis (AD), and reduced microbial richness has been correlated with increased disease severity [10, 27, 28]. In the present study, ovalbumin (OVA) sensitization induced a marked reduction in microbial diversity, whereas synbiotic supplementation restored phylogenetic diversity and significantly altered the overall microbial community structure [29-32]. Notably, in the present study, the synbiotics group exhibited increased abundances of Bacteroidaceae, Lactobacillaceae, and Bifidobacteriaceae. These families include well-characterized taxa associated with SCFA production and are widely reported to play immunoregulatory and anti-allergic roles in maintaining gut barrier homeostasis [33]. Consistent with these family-level shifts, OTU-level analysis revealed a selective enrichment of SCFA-producing genera, including Bacteroides acidifaciens, Bifidobacterium pseudolongum, Lactobacillus crispatus, and Roseburia intestinalis, in the synbiotic group. Collectively, these compositional changes suggest that synbiotic supplementation favors a microbial community structure associated with enhanced SCFA-producing capacity, which is consistent with the observed immunomodulatory effects and attenuation of allergic inflammation [34, 35]. These findings support a mechanistic framework in which prebiotic-driven microbial remodeling and probiotic-mediated immune modulation act in a complementary manner to exert enhanced synbiotic effects.

SCFAs are potent immunomodulators that suppress allergic inflammation by promoting the differentiation of regulatory T cells (Tregs) while inhibiting Th2- and Th17-cell differentiation through mechanisms such as histone deacetylase (HDAC) inhibition [34-36]. Beyond their direct effects on immune cell differentiation, SCFAs have also been shown to modulate epithelial–immune crosstalk, thereby attenuating epithelial stress responses that initiate type 2 inflammation [37]. In line with these mechanisms, synbiotic administration in the present study was associated with coordinated reductions in Th2- and Th17-associated cytokines, together with downregulation of epithelial-derived alarmins, including thymic stromal lymphopoietin (TSLP) and interleukin-33 (IL-33), across gut, skin, and lung tissues. As IL-33 and TSLP are known upstream triggers of type-2 inflammatory pathways and central regulators of the atopic march [38, 39], their downregulation suggests that synbiotics may directly interfere with early events that drive allergic sensitization and disease propagation. Decreases in serum IgE and reduced accumulation of mast cells and eosinophils in affected tissues further corroborate the immunomodulatory actions, indicating attenuation of downstream effector pathways central to allergic inflammation.

Within the respiratory tract, OVA-challenged mice displayed typical asthma-like inflammation, including elevated BALF inflammatory cells, enhanced Th2 cytokine expression, and mucus overproduction. Synbiotic supplementation substantially lessened inflammatory cell recruitment, normalized airway histopathology, and reduced expression of IL-4, IL-5, IL-13, IL-17, TSLP, IL-33, and TARC. The magnitude of improvement suggests that targeting epithelial alarmins and downstream Th2/Th17 pathways may be critical in preventing the progression from AD to allergic airway disease, consistent with the conceptual framework of the atopic march [3, 36, 39].

Together, these findings extend beyond descriptive microbiota alterations and highlight a mechanistic pathway through which synbiotic supplementation integrates microbial metabolism, immune regulation, and epithelial signaling to mitigate allergic inflammation across the gut–skin–lung axis. Collectively, these results support the potential of the combination of L. lactis LB1022 and FOS as a dietary approach for reducing AD severity and modulating the progression of the atopic march.

Supplemental Materials

Supplementary data for this paper are available on-line only at http://jmb.or.kr.