Gut–Brain Axis Research: IDCC 3201 and IDCC 3501 Modulate Neuroinflammatory and BDNF-Related Biomarkers

The gut–brain axis is a complex communication network connecting the gastrointestinal tract, gut microbiota, immune system, and central nervous system. Growing research interest has focused on how microbial components may influence neuroimmune responses and biomarkers associated with neuronal function.

A 2026 study published in Current Topics in Lactic Acid Bacteria and Probiotics investigated the effects of heat-killed Lacticaseibacillus rhamnosus IDCC 3201 and Lactiplantibacillus plantarum IDCC 3501, both individually and in combination, on inflammatory and brain-derived neurotrophic factor (BDNF)-related biomarkers.

The findings showed that the IDCC 3201 + IDCC 3501 combination produced a coordinated response: it reduced several inflammation-related markers while increasing BDNF- and synapse-related biomarkers in an inflammatory microglial cell model.

1. Study Design and Experimental Model

The researchers used BV-2 mouse microglial cells, an established cell model for investigating inflammatory responses in the central nervous system.

The bacterial samples were prepared by heat treatment at 100°C for 30 minutes. The study evaluated three preparations:

• Heat-killed Lacticaseibacillus rhamnosus IDCC 3201

• Heat-killed Lactiplantibacillus plantarum IDCC 3501

• A 1:1 mixture of heat-killed IDCC 3201 and IDCC 3501

Cells were pretreated with the bacterial preparations at concentrations of 10⁵, 10⁶, or 10⁷ cells/mL for one hour. Lipopolysaccharide (LPS), at 1 μg/mL, was then added to induce an inflammatory response, and the cells were incubated for a further 24 hours.

The researchers measured inflammatory gene expression, cytokine secretion, BDNF-related markers, and cell viability using qRT-PCR, ELISA, and Western blotting.

2. Key Research Findings

Finding 1. No Cytotoxicity in BV-2 Microglial Cells

Before evaluating the biological responses, the researchers assessed the cytotoxicity of all three preparations.

• Cell viability remained comparable to the untreated control.

• No significant cytotoxic effects were observed at concentrations ranging from 10⁵ to 10⁷ cells/mL.

• These results supported the use of the tested concentration range in subsequent experiments.

Finding 2. Reduced Expression of Inflammation-Related Genes

LPS stimulation increased the expression of four inflammation-related genes: Tnf, Il1b, Il6, and Ptgs2.

At 10⁷ cells/mL, the IDCC 3201 + IDCC 3501 mixture significantly reduced the expression of all four genes compared with the LPS-treated control.

Inflammatory gene	Reduction vs. LPS control	p-value
Tnf	43.3%	0.0002
Il1b	45.4%	0.0001
Il6	47.2%	0.0004
Ptgs2	35.0%	0.0377

The individual strains showed more selective responses. IDCC 3201 significantly reduced Tnf and Il6 expression, while IDCC 3501 significantly reduced Il1b expression.

In comparison, the combination demonstrated a broader response across all four inflammatory markers.

Finding 3. Reduced Secretion of Pro-inflammatory Cytokines

The researchers also measured the levels of TNF-α, IL-1β, and IL-6 released into the culture medium.

At 10⁷ cells/mL, the IDCC 3201 + IDCC 3501 mixture significantly reduced the secretion of all three cytokines.

Inflammatory cytokine	Reduction vs. LPS control	p-value
TNF-α	63.1%	<0.0001
IL-1β	33.1%	<0.0001
IL-6	43.3%	0.0019

Notably, the individual strain treatments did not produce statistically significant reductions in IL-6 secretion, whereas the combination did.

These findings indicate that the observed response extended beyond changes in gene expression to include reduced extracellular cytokine levels.

Finding 4. Increased BDNF and Synapse-Related Gene Expression

BDNF is a neurotrophic protein associated with neuronal survival, synaptic plasticity, and processes involved in learning and memory.

The study also examined Dlg4, the gene encoding postsynaptic density protein 95 (PSD-95), a protein involved in synaptic organization.

LPS stimulation reduced both Bdnf and Dlg4 mRNA expression. Treatment with the bacterial preparations partially restored these markers.

At 10⁷ cells/mL, the IDCC 3201 + IDCC 3501 mixture produced the following changes compared with the LPS-treated control:

Biomarker	Increase vs. LPS control	p-value
Dlg4 mRNA	94.1%	<0.0001
Bdnf mRNA	56.4%	0.0029

The individual strains also showed improvements in selected markers. However, the mixture demonstrated a more consistent increase across both Bdnf and Dlg4 expression.

Finding 5. Increased BDNF Secretion and Intracellular Protein Expression

To further investigate the BDNF response, the researchers measured both secreted BDNF and intracellular BDNF protein expression.

The mixture produced notable changes in both measurements:

• BDNF secretion: Increased by 78.7% compared with the LPS control (p < 0.0001).

• Intracellular BDNF protein expression: Increased approximately 6.4-fold compared with the LPS control (p = 0.0002).

The increase in intracellular BDNF protein expression was statistically significant in the combination-treated group, while neither individual strain treatment reached statistical significance for this measurement.

These findings provide additional evidence that the observed BDNF-related response was reflected not only at the mRNA level but also at the protein level.

3. What Makes the Combination Interesting?

One notable aspect of this study is the different response patterns observed between the two individual strains.

• IDCC 3201: Demonstrated relatively pronounced effects on selected inflammation-related markers.

• IDCC 3501: Showed more evident effects on BDNF- and Dlg4-related markers.

• IDCC 3201 + IDCC 3501: Demonstrated a broader response across both inflammatory and BDNF-related biomarkers.

This complementary response pattern suggests that combining strain-specific microbial components may be a useful approach when developing postbiotic-type ingredients targeting multiple biological markers.

However, the authors emphasized that the findings do not establish synergistic activity or definitive superiority over individual strains. Further studies are required to clarify the mechanisms behind the observed responses.

4. Research Implications and Limitations

The study provides preliminary evidence that heat-killed IDCC 3201 and IDCC 3501 may influence inflammatory and neurotrophic biomarker responses in microglial cells.

From a functional ingredient development perspective, the results are particularly relevant to research exploring microbial components and their potential relationship with neuroimmune responses.

Several limitations should nevertheless be considered:

• The experiments were conducted using BV-2 mouse microglial cells, not human participants or animal models.

• The study did not directly evaluate cognitive function, memory, neuronal protection, or synaptic activity.

• The underlying signaling pathways, including NF-κB/MAPK and TrkB/CREB/Akt, were not directly investigated.

• The study did not identify the specific bacterial components responsible for the observed effects.

Therefore, the findings should be interpreted as preliminary in vitro evidence of biomarker modulation rather than proof of neuroprotective or cognitive benefits.

Conclusion

The combination of heat-killed IDCC 3201 and IDCC 3501 demonstrated a coordinated response across inflammatory and BDNF-related biomarkers in LPS-stimulated BV-2 microglial cells.

The mixture significantly reduced the expression of four inflammatory genes and the secretion of three pro-inflammatory cytokines. At the same time, it increased Bdnf and Dlg4 mRNA expression, BDNF secretion, and intracellular BDNF protein expression.

These findings highlight the research potential of strain-defined postbiotic-type preparations in the emerging field of microbiota–brain research. Further pathway-level investigations and in vivo studies will be important to determine whether these cellular responses translate into meaningful physiological outcomes.

At ILDONG Bioscience, we continue to explore the strain-specific properties of probiotics and postbiotic materials, supporting the development of scientifically characterized microbial ingredients for emerging functional health applications.