The research team, led by Shenji Wu and corresponding author Delin Qi of Qinghai University’s State Key Laboratory of Plateau Ecology and Agriculture, together with Fei Tian of the Northwest Institute of Plateau Biology at the Chinese Academy of Sciences, combined liver and blood biochemistry with transcriptome-wide gene expression profiling. They also tracked the expression of key immune-related genes in the gills and spleen, the two organs that sit at the front line of a fish’s interaction with its watery environment. By integrating biochemical measurements with mRNA expression data, the researchers were able to connect physiological damage with the genetic machinery that responds to it, painting a dynamic picture of immune regulation under oxygen stress.

The clearest signal emerged from the comparison between the two hypoxia regimes. Severe short-term hypoxia, the twelve-hour acute challenge, exacerbated oxidative damage in the fish and significantly altered the expression of genes governing apoptosis, the controlled program of cell death, and autophagy, the cellular recycling process that degrades damaged components. This makes intuitive biological sense: when oxygen supply collapses suddenly, mitochondria leak reactive oxygen species, membranes are peroxidized, and cells must decide whether to repair themselves or self-destruct. Malondialdehyde, a standard marker of lipid peroxidation, served as one of the biochemical readouts of this damage, alongside antioxidant enzymes such as total superoxide dismutase and catalase, which mop up reactive oxygen species before they can wreak havoc.

At the pathway level, the transcriptomic response to severe short-term hypoxia was strikingly specific. Gene sets involved in phagosome function, lysosomal activity, Toll-like receptor signaling and NOD-like receptor signaling were all significantly enriched under the acute challenge. These pathways form the backbone of the innate immune system: phagosomes and lysosomes engulf and digest cellular debris and invading microbes, while TLRs and NLRs are pattern-recognition receptors that detect molecular signatures of pathogens and tissue damage. Notably, none of these pathways showed comparable enrichment under moderate prolonged hypoxia, suggesting that the fish’s immune system interprets a sudden oxygen crash as an emergency requiring full innate immune mobilization, whereas a gradual, sustained oxygen decline is managed through quieter, more homeostatic mechanisms.

To move beyond simple lists of differentially expressed genes, the researchers applied two complementary computational approaches. Short Time-series Expression Miner, or STEM, was used to identify genes that follow coherent temporal expression profiles across the moderate hypoxia time course of 24, 96 and 168 hours. Weighted Gene Co-expression Network Analysis, or WGCNA, was then used to detect modules of genes that behave in a coordinated fashion and to link those modules to the measured biochemical traits. Together, these methods pinpointed a set of key immune-related genes whose expression patterns define the fish’s hypoxic immune response, including nod1, irf3, ifnα, pi3k, akt, p38, il-12, jak1, stat1, nlrp3, bax, bcl2, bcl-xl, atg5 and lc3.

Each of these genes tells part of the story. NOD1 is an intracellular pattern-recognition receptor that senses bacterial peptidoglycan and triggers inflammatory signaling. IRF3 and interferon alpha sit at the heart of the antiviral response, while the IL-12, JAK1 and STAT1 axis connects innate detection to the activation of adaptive immune cells. PI3K and AKT are central survival kinases that also feed into autophagy regulation, and the BAX, BCL2 and BCL-XL proteins are the arbiters of the mitochondrial apoptosis pathway, deciding whether stressed cells live or die. ATG5 and LC3 are core components of the autophagy machinery itself, and NLRP3 is the inflammasome sensor that can ignite potent inflammatory responses. The fact that most of these genes showed similar expression trends in the hypoxia-challenged gills indicates that the respiratory epithelium, in constant contact with the oxygen-poor water, orchestrates a coordinated immune program.

The spleen told its own story. In this immune organ, the expression of nod1, irf3, akt, pi3k, jnk and cyld was remarkably induced by severe short-term hypoxia. CYLD, a deubiquitinating enzyme, acts as a brake on inflammatory signaling pathways including NF-κB, so its induction alongside NOD1 and IRF3 suggests a carefully balanced response: the fish activates antiviral and antibacterial defenses while simultaneously engaging negative regulators to prevent runaway inflammation. This kind of calibrated response is critical, because uncontrolled inflammation in a hypoxic animal can compound tissue damage rather than repair it. The spleen’s sensitivity to the acute challenge underscores that hypoxia is not merely a respiratory problem but a systemic immune event.

Why does this matter beyond the biology of one Tibetan fish? Aquatic hypoxia is an increasingly common stressor in natural waters and aquaculture systems alike, driven by eutrophication, warming temperatures and high stocking densities. Hypoxic episodes suppress growth, impair immune competence and increase susceptibility to disease in farmed fish, imposing substantial economic losses. Understanding how a naturally hypoxia-tolerant species regulates its immune system under different oxygen regimes provides a template for what robust fish look like at the molecular level. The authors explicitly frame their results as valuable information for breeding hypoxia-tolerant fish, and the gene set they identified, from pattern-recognition receptors to apoptosis regulators, offers candidate markers for selective breeding or genome editing programs aimed at hardier aquaculture stocks.

The study also carries a broader conceptual message about how stress biology should be measured. Had the researchers tested only a single hypoxia condition or a single time point, they might have concluded that hypoxia uniformly activates innate immune pathways. Instead, the contrast between severe short-term and moderate prolonged exposure reveals that the nature of the stressor, not just its presence, determines the immune strategy. Acute severe hypoxia triggers oxidative damage, cell-death decisions and full innate immune mobilization, while chronic moderate hypoxia appears to be absorbed without triggering the same pathway-level enrichment, implying that the fish either adapts metabolically or relies on regulatory mechanisms that do not register as classical immune activation in the transcriptome.

For Gymnocypris eckloni itself, the work adds a new dimension to its reputation as a survivor of the roof of the world. Plateau fishes face a double challenge: cold temperatures slow their metabolism while low oxygen constrains their aerobic capacity, and immune defenses are energetically expensive to maintain. The dynamic regulation documented in this study, with its interplay of phagocytosis, inflammasome signaling, interferon responses, apoptosis and autophagy, shows that tolerance to hypoxia is not a passive tolerance of damage but an actively managed physiological state. As climate change alters oxygen dynamics in lakes and rivers worldwide, the molecular playbook of this high-altitude fish may prove to be one of the most valuable resources aquaculture and conservation biology have yet uncovered, and the Qinghai-Tibetan Plateau continues to yield insights found nowhere else on Earth.

Subject of Research: Immune gene regulation in the Tibetan plateau fish Gymnocypris eckloni under severe short-term and moderate prolonged hypoxia

Article Title: Dynamic immune regulation of Gymnocypris eckloni in response to severe short-term hypoxia and moderate prolonged hypoxia

Article References: Wu, S., Wang, Z., Xia, M., Liu, D., Wang, W., Zhang, C., Jia, J., Tian, F., & Qi, D. (2026). Dynamic immune regulation of Gymnocypris eckloni in response to severe short-term hypoxia and moderate prolonged hypoxia. BMC Genomics. https://doi.org/10.1186/s12864-026-13296-4

Image Credits: AI Generated

DOI: 10.1186/s12864-026-13296-4

Keywords: hypoxia, Gymnocypris eckloni, immune regulation, transcriptome, Qinghai-Tibetan Plateau, innate immunity, apoptosis, autophagy, TLR signaling, NLR signaling, WGCNA, aquaculture

A new review published in MicrobiologyOpen examines whether plant-derived compounds could help fill this gap, not by mimicking existing antivirals but by targeting the host signaling pathways that influenza exploits. The work is timely because severe influenza is often driven less by direct viral damage than by immune dysregulation, particularly the excessive cytokine production known as a cytokine storm, which contributes substantially to pulmonary pathology and mortality. Central to this process are key signaling cascades, including the Toll-like receptors (TLRs), the retinoic acid-inducible gene I (RIG-I) pathway, the mitogen-activated protein kinase (MAPK) cascades, and nuclear factor kappa B (NF-κB), which orchestrate antiviral responses through interferon and cytokine induction but can also drive immunopathology when aberrantly activated. The review, which surveyed literature from 2000 to 2025 and focused specifically on human IAV subtypes H1N1 and H3N2, argues that phytochemicals capable of both inhibiting viral replication and fine-tuning these pathways could serve as adjunctive therapies.

The evidence base begins at the level of innate immune recognition. TLR3, TLR7, and TLR8 detect viral RNA species generated during IAV replication, while TLR4 is activated indirectly by host-derived damage-associated molecular patterns released during infection-induced oxidative stress. TLR3 signaling through the adaptor TRIF activates TBK1 and IRF3 to induce IFN-β, yet overexpression of this interferon can itself contribute to cytokine storm and lung damage. Autopsy studies of fatal influenza cases have revealed prolonged TLR4 and MyD88 expression in lung tissue, illustrating that the TLR4/MyD88/NF-κB axis is a double-edged sword, essential for initiating antiviral immunity but potentially detrimental when dysregulated. Against this backdrop, several flavonoids have shown the ability to dampen TLR signaling. Quercetin reduced H1N1-induced cell death and activation of the TLR7/NF-κB p65 axis in a human bronchial epithelial co-culture model, while dihydromyricetin inhibited TLR3 and TRIF expression in infected lung epithelial cells, lowering pro-inflammatory cytokines such as CCL5, IP-10, and MIG.

Notably, dihydromyricetin also demonstrated genuine dual activity, reducing H1N1 and H3N2 plaque formation in a concentration-dependent manner with IC50 values between 11.67 and 23.33 micromolar, and binding the PB2 subunit of the viral polymerase in mini-replicon and surface plasmon resonance assays. Epigallocatechin gallate (EGCG), the major green tea catechin, targets an early stage of the replication cycle of both H1N1 and H3N2 with EC50 values of 5.7 to 17.3 micromolar, and oral administration reduced TLR4 and NF-κB protein levels in a mouse model of H9N2-induced lung injury. Curcumin, the polyphenol from turmeric, engaged TLR, MAPK, and NF-κB signaling concurrently while directly inactivating virions and blocking viral adsorption, and in mice it reduced lung viral titers, inflammatory cytokines, and mortality. Carvacrol, a phenolic compound from Mosla chinensis, downregulated TLR7, RIG-I, MyD88, and NF-κB in infected mice while reducing lung viral RNA load and pulmonary injury.

The RIG-I pathway presents a more nuanced picture. This cytosolic receptor detects viral RNA and, through the mitochondrial adaptor MAVS, activates IRF3 and NF-κB to drive interferon production and chemokine release, yet some studies suggest RIG-I-mediated recruitment of monocyte-derived dendritic cells can paradoxically enhance viral replication in infected lungs. The flavonoid apigenin suppresses this pathway by promoting RIG-I degradation: it disrupts the stabilizing interaction between RIG-I and the chaperone Hsp90α, enhancing ubiquitination by the E3 ligase RNF125 and proteasomal destruction of the receptor. This reduces the cell’s capacity to sense viral RNA and mount type I interferon responses, potentially limiting virus-induced inflammation, and apigenin also dose-dependently decreased expression of viral proteins NS1, NP, M1, and M2 in A549 cells. Similarly, the triterpenoid pterodontic acid reduced viral propagation by inhibiting viral ribonucleoprotein export while lowering RIG-I expression and downstream inflammatory mediators, and the phytosterol β-sitosterol disrupted RIG-I-mediated STAT1 activation, reducing IL-6, IL-8, TNF-α, and IP-10 production.

The MAPK pathway illustrates perhaps the most mechanistically interesting dimension of phytochemical action, because different compounds manipulate the same kinases in opposite directions with antiviral benefit in both cases. ERK1 signaling facilitates the nuclear export of viral ribonucleoprotein complexes, a critical step in the IAV replication cycle, so blocking ERK phosphorylation directly restricts propagation. The isoquinoline alkaloid berberine blocked H1N1 growth in macrophages and epithelial cells by interfering with ERK1-mediated vRNP nuclear export, while patchouli alcohol, a sesquiterpene from Pogostemonis herba, suppressed ERK1/2 activation with clear anti-influenza activity across multiple H1N1 strains. Conversely, EGCG and the compound DMO-CAP activate rather than inhibit MAPK cascades to enhance antiviral host programs: EGCG induces human β-defensin 3 and IFN-λ2 expression through p38, ERK, and JNK activation, while DMO-CAP triggers the Nrf2/HO-1 axis, which amplifies interferon-stimulated genes. This apparent paradox is resolved by recognizing that ERK inhibition disrupts pro-viral vRNP export whereas ERK activation promotes antiviral interferon induction, both mediated through the same kinase.

NF-κB adds a further layer of complexity because it serves the virus directly as well as the host. Beyond driving inflammatory gene expression, NF-κB signaling is required for viral genomic RNA synthesis and induces pro-apoptotic factors such as TRAIL and Fas ligand, which facilitate caspase-mediated nuclear export of vRNPs. Pterodontic acid exploits this dependency by inhibiting TRAIL and FasL expression, downregulating caspase-3/7 activity and impairing vRNP export. The flavonoid cirsimaritin reduced NF-κB p65 nuclear phosphorylation in infected THP-1 cells while suppressing multiple IAV subtypes with IC50 values of 5.8 to 11.1 micrograms per milliliter, and andrographolide, a diterpenoid from Andrographis paniculata, increased survival and reduced viral loads in a lethal H1N1 mouse model, with a combination study showing that pairing it with a viral entry inhibitor produced greater survival benefit than either compound alone. Among extracts, total flavonoids from Mosla scabra reduced lung viral load and inflammatory infiltration in mice more effectively than amantadine at the highest dose tested, and total flavones from Abelmoschus manihot suppressed viral RNA by day three post-infection in vivo.

The review is candid about the field’s weaknesses, and these are substantial. Many studies assess cytokine markers without measuring infectious viral titers, making it impossible to distinguish direct antiviral effects from indirect immunomodulation that merely creates a less permissive environment. Molecular binding targets are rarely identified, and the concentrations used in cell culture consistently exceed what is pharmacokinetically achievable in human lung tissue. Quercetin’s oral absorption in humans ranges from only 3 to 17 percent, with peak plasma levels rarely exceeding 1 to 2 micromolar, far below the 10 to 50 micromolar concentrations used in vitro. Berberine’s oral bioavailability falls below 5 percent due to P-glycoprotein efflux and hepatobiliary re-excretion, β-sitosterol’s is approximately 0.41 percent, and EGCG undergoes extensive gastrointestinal degradation. No pharmacokinetic data exist for any compound reviewed in bronchoalveolar lavage fluid or lung tissue, the primary site of replication, and safety concerns such as EGCG-associated hepatotoxicity at high supplemental doses and CYP enzyme inhibition that could affect co-prescribed drugs add further complications.

Despite these barriers, the review identifies a clear path forward. Because TLR and RIG-I signaling converge on shared components such as TRAF6, TAK1, and IRF3, compounds like miquelianin and carvacrol can engage multiple pathways through a single molecular target, functioning as modulators of an integrated innate immune network rather than selective inhibitors of discrete cascades. The authors recommend that molecular target identification through thermal shift assays and docking validation become standard practice, that pharmacokinetic evaluation be extended to respiratory tissue rather than plasma alone, that human airway organoid models serve as physiologically relevant intermediates, and that crude extracts undergo bioassay-guided fractionation to define active constituents. Clinical translation to date has involved complex extracts such as standardized black elderberry and Cistus incanus preparations, with limited or inconsistent results, and none of the defined phytochemicals discussed has yet entered a dedicated anti-influenza trial. If the recommended mechanistic rigor is adopted, the structural diversity and broad immunomodulatory activity of these plant compounds represent a genuine and underexploited opportunity for host-directed adjunctive therapy against a virus that continues to outpace the limited drugs available against it.

Subject of Research: Immunomodulatory and antiviral effects of phytochemicals on host signaling pathways during influenza A virus infection

Article Title: Dual Antiviral and Immunomodulatory Effects of Phytochemicals in Influenza A Virus Infection: Targeting Key Host Signaling Pathways

Article References: Chowdhury, D., Vanderven, H. A., Wangchuk, P., & Sarker, S. (2026). Dual Antiviral and Immunomodulatory Effects of Phytochemicals in Influenza A Virus Infection: Targeting Key Host Signaling Pathways. MicrobiologyOpen, 15(5), Article e70424. https://doi.org/10.1002/mbo3.70424

Image Credits: AI Generated

DOI: 10.1002/mbo3.70424

Keywords: influenza A virus, phytochemicals, TLR signaling, RIG-I, MAPK, NF-κB, cytokine storm, flavonoids, antiviral therapy, immunomodulation, host-directed therapy, natural products