The preparation, dubbed PL-tLB, consists of two bacterial strains, Lactobacillus plantarum VIOAP03 and Lactobacillus fermentum VIMPP04, combined in a one-to-one volume ratio. Both strains were deposited with the Korean Collection for Type Cultures, and one of them was cultured in a medium enriched with P. linteus concentrate before harvesting. The mixture was then subjected to tyndallization, a repeated heating process named after the nineteenth-century physicist John Tyndall that renders bacterial cells nonviable while preserving many of their structural components. The final product was flash-frozen in liquid nitrogen, freeze-dried, and standardized to contain at least one hundred billion nonviable cells per gram. According to the authors, this approach sidesteps a central weakness of live probiotics, which can lose viability during storage and gastrointestinal transit and, in vulnerable patients, carry a small risk of microbial translocation.

Tyndallized bacteria belong to a category of products sometimes called paraprobiotics or postbiotic-related materials. Although dead cells cannot perform metabolic activity, their cell walls, peptidoglycans, and other surface molecules can still interact with immune cells and modulate inflammatory signaling pathways. Previous work with heat-killed Lactobacillus rhamnosus, for example, showed reduced immunoglobulin E levels in a mouse model of atopic dermatitis. The Korean team reasoned that bacteria living in symbiosis with a medicinal mushroom might carry particularly potent immunomodulatory properties, since the mushroom itself is rich in polysaccharides, phenolic compounds, terpenoids, and proteins with documented anti-inflammatory and antioxidant effects.

The first experiments used HaCaT cells, a widely studied line of human keratinocytes, the dominant cell type of the outer epidermis. When keratinocytes are stimulated with the inflammatory signals TNF-alpha and IFN-gamma, they mimic the cytokine milieu of an atopic dermatitis lesion, ramping up production of chemokines such as CCL17/TARC and CCL22/MDC, both recognized biomarkers of the disease, along with the proinflammatory cytokines IL-1beta, IL-6, and IL-8. Treatment with PL-tLB suppressed the expression of all of these mediators in a concentration-dependent manner, measured both at the messenger RNA level by real-time PCR and at the protein level by enzyme-linked immunosorbent assay. At a concentration of thirty micrograms per milliliter, the suppressive effect was comparable to that of cyclosporine A, a potent immunosuppressive drug used in severe eczema.

Not every dose was benign. At sixty and one hundred micrograms per milliliter, PL-tLB reduced HaCaT cell viability to below eighty percent, a signal of cellular stress that the authors attribute, hypothetically, to excessive exposure of the cells to bacterial cell wall components such as peptidoglycans and lipoteichoic acids. Importantly, the researchers did not measure, isolate, or deplete any candidate molecules, so the component responsible for the toxicity, and indeed for the anti-inflammatory benefit, remains unknown. All subsequent cell experiments were therefore conducted at three, ten, and thirty micrograms per milliliter, concentrations that preserved viability while retaining biological activity.

The team then moved to an animal model. Thirty female BALB/c mice were divided into groups and given topical applications of DNCB, 2,4-dinitrochlorobenzene, a chemical sensitizer that reliably induces atopic dermatitis-like lesions on mouse skin. After an initial sensitization week, both ears of each mouse were challenged twice weekly for three weeks, while the animals received daily oral gavage of PL-tLB at three escalating doses, or dexamethasone as a positive control. Four weeks of DNCB exposure produced the expected pathology: swollen ears, thickened epidermis and dermis, and dense infiltration of mast cells, the immune cells whose granules release histamine and drive the itching characteristic of eczema. Mice treated with PL-tLB showed significantly reduced ear thickness, less epidermal and dermal hypertrophy on hematoxylin and eosin staining, and fewer mast cells on toluidine blue staining compared with untreated DNCB animals.

The immunological fingerprints of the disease were also blunted. Atopic dermatitis is driven largely by T helper type 2 cells, which stimulate B cells to secrete immunoglobulin E, the antibody class responsible for allergic hypersensitivity, along with shifts in IgG subclasses. Serum levels of IgE, IgG1, and IgG2a all rose in DNCB-treated mice and fell significantly after PL-tLB administration. Notably, at the highest dose of one hundred billion cell equivalents per kilogram of body weight, the preparation suppressed IgE more effectively than dexamethasone in this experiment. Real-time PCR analysis of ear tissue confirmed the pattern at the transcriptional level, with dose-dependent reductions in the messenger RNA for IL-1beta, IL-4, IL-6, TNF-alpha, CCL17, and CCL22, and effects at the highest dose similar to those of the steroid control.

Perhaps the most intriguing finding concerned the skin barrier itself. DNCB exposure sharply reduced expression of filaggrin, involucrin, and loricrin, three structural proteins essential for the integrity of the stratum corneum, the outermost layer of the epidermis. Filaggrin deficiency in particular is a well-established genetic risk factor for atopic dermatitis, because it compromises the skin’s ability to retain moisture and exclude allergens. PL-tLB treatment produced a concentration-dependent partial recovery of all three genes. The preparation also restored, at least in part, the expression of tight junction components, including claudin-4, occludin, and tight junction protein 1, which seal the gaps between keratinocytes and provide a second, deeper line of defense complementary to the stratum corneum. A treatment that addresses both inflammation and barrier architecture simultaneously would represent a meaningful departure from therapies that suppress symptoms alone.

The authors are careful to frame the work as preclinical. Because the two bacterial strains were tested only as a combined mixture, their individual contributions, and any possible synergy between them, cannot be disentangled from the present data. The in vitro and in vivo experiments used different dosing metrics, micrograms per milliliter in cell cultures versus cell equivalents per kilogram in mice, and no validated conversion between the two was established. The study also did not assess pharmacokinetics, tissue distribution, or long-term safety, and no human efficacy can be inferred from mouse models. Future work, the researchers write, should fractionate the preparation, test each strain alone under matched conditions, and apply formal interaction analyses to determine whether the combined response is synergistic, additive, or driven by a single dominant component.

Even with those caveats, the study offers a compelling proof of concept that bacteria harvested from a medicinal mushroom and killed by heat can retain meaningful anti-inflammatory and barrier-protective activity. If the active molecules can be identified and standardized, tyndallized preparations could offer a shelf-stable, infection-free alternative to live probiotics for managing atopic dermatitis, a disease whose global prevalence continues to climb. For now, the humble Sanghwang mushroom has yielded more than polysaccharides: it has offered up two strains of lactic acid bacteria whose inert remains, in mice at least, quiet the immune storm and begin to rebuild the skin’s broken walls.

Subject of Research: Effects of tyndallized lactic acid bacteria from Phellinus linteus on atopic dermatitis-like inflammation and skin barrier damage

Article Title: Effects of tyndallized lactic acid bacteria separated from Phellinus linteus on inflammation and skin barrier damage induced by DNCB

Article References: Bak, S. G., Cheon, Y. J., Chandimali, N., Lim, H. J., Won, Y.-S., Kwon, H. S., Oh, H., Yun, S.-I., Lee, S. W., Bae, J., Kim, S., & Lee, S.-J. (2026). Effects of tyndallized lactic acid bacteria separated from Phellinus linteus on inflammation and skin barrier damage induced by DNCB. Archives of Dermatological Research, 318(1), Article 450. https://doi.org/10.1007/s00403-026-04963-3

Image Credits: AI Generated

DOI: 10.1007/s00403-026-04963-3

Keywords: atopic dermatitis, Phellinus linteus, tyndallized bacteria, postbiotics, skin barrier, tight junctions, filaggrin, lactic acid bacteria, DNCB, mast cells, immunoglobulin E, keratinocytes