Cytokines and type 1 diabetes

In T1DM, a process known as insulitis occurs, where immune cells infiltrate pancreatic islets, attacking and destroying the insulin-producing β cells. Cytokines, including IL-1, IL-6, and TNF-α, are key players, with some, like IL-1β and IFN-γ, promoting inflammation and others directly inducing β-cell death. This autoimmune destruction of β cells results in a lack of insulin and lifelong insulin dependence in affected individuals [13]. Immune system dysregulation can lead to β-cell destruction in T1DM through the action of pro-inflammatory cytokines like IL-6, IL-17, IL-21, and TNF-α, which promote the function and differentiation of immune cells that target β cells (Figure 2). These cytokines orchestrate the autoimmune response by activating harmful immune cells and contributing to the inflammatory environment that destroys these insulin-producing β cells [14–16]. However, regulatory T cells (Tregs) use suppressive cytokines like IL-10 and TGF-β to dampen immune responses and maintain immune homeostasis. These cytokines inhibit the activation and proliferation of other immune cells, acting as a crucial mechanism to prevent autoimmune diseases and protect vital cells like β cells [17–19].

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Figure 2. Chronic inflammation, β-cell dysfunction, and diabetes: ligand (cytokines)-receptor interaction activates cytoplasmic kinases leading to increased transcription of nuclear factor kappa beta (NF-κB), activator protein 1 (AP-1), and signal transducer and activator of transcription 1 (STAT1). This results in increased production and secretion of proinflammatory cytokines, perpetuating the inflammatory cascade and increased M1 macrophages. Chronicity of inflammation finally contributes to β-cell dysfunction or death. Interaction of damage-associated molecular proteins (DAMPs) with their receptors causes activation of NF-κB, followed by NOD-, LRR-, and pyrin domain-containing protein 3 (NLRP3) inflammasome, contributing to increased IL-1β involving caspase 1. This results in the development of type I and type II diabetes. Akt: protein kinase B; ERK: extracellular signal-regulated kinase; IFN: interferon; IL: interleukin; IRAKM: interleukin-1 receptor-associated kinase 3; JAK: Janus kinase. PI3K: phosphoinositide 3-kinase; RANK: receptor activator of nuclear factor-kappa B; TLRs: toll-like receptors; TNF: tumor necrosis factor. Created in BioRender. Rai, V (2025) https://BioRender.com/soxbxwk.

While previous research, mainly from animal studies, had ambiguous or conflicting results about the role of IL-17, Arif et al. [20], using 50 human patients, reported the direct involvement of an immune protein called IL-17 in the destruction of insulin-producing β cells in humans. This study provides clear evidence that T-cells from T1DM patients secrete IL-17 in response to their own β cells [20]. The researchers found that this cytokine is present in the inflamed pancreas of patients at the onset of the disease, suggesting its key role in a multi-step process that leads to β-cell death. The study proposed a two-part pathway for β-cell death. It shows that other inflammatory cytokines, such as IL-1β and IFN-γ, act first to “prime” the β cells by making them highly susceptible to IL-17. This priming happens when the β cells, in response to these early inflammatory signals, increase their expression of the IL-17 receptor (IL-17RA). This leads to the activation of specific molecular pathways, such as signal transducer and activator of transcription 1 (STAT1) and NF-κB, driving the destruction of β cells. This study fundamentally changes the understanding of β-cell destruction by showing that the β cells are not just passive victims; they actively participate in their own demise by becoming more vulnerable to the damaging effects of IL-17 [20]. The study also reported that the immune response involving IL-17-producing cells closely resembles that of TH1 cells. While the full scope of this β-cell-specific T-cell response is not yet fully understood, the study provides evidence that a prominent polarization toward the IL-17 pathway is actively promoted around the time of diagnosis. This finding is significant because the differentiation of these TH17 cells can be influenced by environmental factors, which align with evidence for non-genetic causes of the disease. Furthermore, since these cells are known to be more resistant to regulation by other immune cells, this could explain why the immune systems of T1DM patients are less “regulatable”. Given that human β cells are susceptible to IL-17, these findings provide a strong justification for developing new treatments that target the pathways of TH17 cells to halt their destructive activity [20].

Another study by Asif et al. [21], in their review, discussed how the innate immune system plays a crucial role in the development and progression of T1DM through complex cell-cell crosstalk. Various innate immune cells, including dendritic cells, macrophages, and neutrophils, contribute to the disease’s initiation and the destruction of insulin-producing β cells. For example, dendritic cells present β-cell antigens to T cells, activating the immune response, while pro-inflammatory M1 macrophages secrete destructive cytokines like IL-1β. However, these cells also possess the ability to regulate the immune system; for instance, some dendritic cells can promote immune tolerance, while M2 macrophages can support tissue repair. Other cells, like neutrophils and natural killer cells, contribute to β-cell destruction, but recent findings also highlight the potential of innate lymphoid cells (ILCs) to protect β cells and promote immune regulation. Ultimately, the balance between these pro-inflammatory and anti-inflammatory functions shapes the pancreatic environment in T1DM, and strategies that shift this balance toward tolerance hold promise for future therapeutic interventions.

Cytokines and type 2 diabetes

Like T1DM, pro-inflammatory cytokines also play a role in the pathogenesis of T2DM. Pro-inflammatory cytokines like TNF-α, IL-6, and IL-1β are central to T2DM development, creating a chronic inflammatory state in fat tissue and elsewhere that worsens insulin resistance, impairs β-cell function, and drives disease progression by interfering with insulin signaling and recruiting more immune cells, forming a vicious cycle. In T2DM, elevated levels of pro-inflammatory cytokines like TNF-α, IL-6, and IL-1β, often from visceral fat, trigger insulin resistance and metabolic dysfunction. These pro-inflammatory signals interfere with insulin signaling pathways, contributing to the progression of T2DM and its complications. While some cytokines are pro-inflammatory, adipokines such as adiponectin can have beneficial effects, indicating a complex balance of these messengers in T2DM pathogenesis. Pro-inflammatory cytokines like TNF-α and IL-6 directly interfere with the insulin signaling pathway by promoting the phosphorylation of insulin receptor substrates (IRS), which reduces insulin sensitivity [7, 12].

Cytokine imbalances in diabetic wounds

Cytokine imbalance plays an important role in DFUs. Liu et al. [42], in their review, reported that an increase in TNF-α and a decrease in IL-10 lead to defects in the innate immune system, where macrophages that normally should switch from pro-inflammatory M1 pathway to M2 (pro-repair pathways) are defective in DFU patients. This leads to defective transient mechanisms through prolonged M1 phase with little to no M2 involvement (Table 2).

Increased pro-inflammatory cytokines like TNF-α, IL-1β, and IL-6 in DFUs disrupt the normal healing process, creating a persistent inflammatory state that damages tissue and impedes re-epithelialization, fibroblast function, and angiogenesis. Impaired angiogenesis and reduced cell proliferation converge to prevent effective closure of DFUs. Persistent pro-inflammatory cytokines trap wounds in the inflammatory phase, preventing transition to tissue formation and remodeling [47]. Neutrophil and macrophage activity remains excessive, protease release is prolonged, and macrophages fail to shift from the inflammatory M1 to the reparative M2 phenotype. The impaired transition of macrophages disrupts the local signaling required for the appropriate production and release of growth factors needed for healing. Chronic inflammation in DFUs creates a detrimental wound microenvironment that disrupts the normal healing cascade by impairing the production and function of essential growth factors, impeding angiogenesis, and dysregulating immune cells like macrophages. Elevated pro-inflammatory cytokines like TNF-α, IL-1β, and IL-6 disrupt cellular processes, leading to insufficient growth factor signaling necessary for tissue repair, proliferation, and the timely formation of new blood vessels, which ultimately hinders DFU healing and contributes to chronicity [43]. With VEGF and platelet-derived growth factor (PDGF) suppressed, oxygen delivery and granulation remain inadequate [44, 48]. Diabetes-related neuropathy and vascular insufficiency exacerbate these effects, resulting in ulcers that may persist for months or years. Clinically, these wounds are resistant to therapy, promote biofilm growth, and significantly increase the risk of amputation [49]. Chronic inflammation, therefore, locks DFUs in a non-healing state, making cytokine rebalancing essential for recovery.

IFNs play a central role in antiviral immunity and influence wound repair. Elevated IFN signaling, particularly IFN-γ and type I IFN (IFN-α/β), has been implicated in impaired wound healing. IFN-γ prolongs inflammation by stimulating the production of TNF-α and IL-1β by macrophages, while IFN-α/β suppresses VEGF, thereby limiting vascularization [45]. Preclinical studies in diabetic wound models show that excessive IFN activity delays granulation tissue formation, whereas targeted modulation can improve outcomes. For instance, restoration of IFN-κ signaling has been shown to enhance re-epithelialization and collagen organization in murine models [46]. Although clinical evidence remains sparse, IFNs clearly act as a double-edged sword: chronic overexpression exacerbates ulcer chronicity, while carefully modulated application may accelerate closure.

NF-κB is often regarded as the central master inflammatory pathway activated by hyperglycemia, advanced glycation end products (AGEs), and oxidative stress, all seen in DFUs, leading to upregulation of TNF-α, IL-1β, and IL-6 and increased matrix metalloproteinases (MMPs). Nrf2 is a transcription factor that checks NF-κB by promoting antioxidant protein production and downregulating NF-κB expression. Patients with DFUs cannot express Nrf2 as readily, leading to prolonged NF-κB expression. Furthermore, NLRP3 inflammasome amplifies IL-1β production. Mitogen-activated protein kinase (MAPK) pathways and TLR signaling (especially TLR4) crosstalk with NF-κB, causing chronic activation and cytokine release. Dysregulated miRNAs cannot suppress cascades, drive continuous M1 pro-inflammatory states, decrease M2 transition, and impair Treg function [50]. With poor angiogenesis and increased MMPs (excess ECM remodeling/degradation) from chronic activation, therapeutic approaches should inhibit NF-κB, inflammasome activity, enhance Nrf2, or promote M2 polarization [50].

Impact of altered cytokines on wound healing

DFUs are marked by chronic inflammation and hyperglycemia. This leads to a profound cytokine imbalance. Pro-inflammatory cytokines (TNF-α, IL-1β, IL-6) remain upregulated, while anti-inflammatory and pro-healing factors (IL-10, TGF-β, VEGF) are downregulated. This affects key pathways, like NF-κB and MAPK, disrupting mechanisms required for wound healing [48]. This disrupted cytokine environment has downstream effects on wound-healing cells [51]. For example, the increased presence of TNF-α and IL-1β inhibits both the proliferation and migration of fibroblasts and keratinocytes, while continued activation of NLRP3 further impairs keratinocyte mobility. Consequently, the granulation tissue formed is weak and nonfunctional [46]. These cellular dysfunctions set the stage for subsequent complications affecting the vascular and structural aspects of wound repair. Building on this, endothelial dysfunction emerges as a major barrier to healing because angiogenesis is severely impaired. TNF-α and IL-1β drive reactive oxygen species (ROS) and protease activities while activating NF-κB, actions that inhibit VEGF signaling and induce endothelial apoptosis [45]. Additionally, p38 MAPK activation by IL-1β and decreased TGF-β1/Smad3 signaling further impede new vessel formation [46].

These changes in the vascular and inflammatory environments directly influence ECM remodeling in DFUs. The imbalance in cytokines increases MMPs (e.g., MMP-9) activity, leading to degradation of structural proteins such as collagen and fibronectin [44]. Simultaneously, fibroblasts in this pathogenic setting generate less ECM, which creates structural voids in the matrix and ultimately halts the tissue remodeling phase due to a lack of effective substrate for cell adhesion and growth factor signaling [46, 50]. The interconnectedness between cellular, vascular, and structural defects emphasizes the complexity of impaired wound healing in DFUs. A persistent presence of M1 macrophages and persistently high TNF-α, IL-β, IL-6, iNOS, and MMP-9 leads to inflammation, ECM degradation, and impaired repair [44].

Reduced cell proliferation and migration

The persistent inflammation mediated by TNF-α, IL-1β, and IL-6 in DFUs hinders the proliferation, migration, and functioning of critical cellular populations, including endothelial cells, fibroblasts, and keratinocytes needed for key healing events such as collagen deposition, ECM formation, and re-epithelialization[52]. This results in MMPs-mediated collagen degradation and reduction in growth factors, eroding the repairing scaffold [42]. This leads fibroblasts toward senescence and reduced ECM production and compromises wound closure with fragile tissue. Fibroblasts’ heterogeneity and plasticity, regulated by cytokines, also play a role in impaired healing by affecting ECM production and angiogenesis [53]. Further mechanistic insights have described roles for cytokines such as TNF-α secreted from M1 macrophages, which upregulate keratinocyte expression of tissue inhibitors of metalloproteinases (TIMP) -1, thereby restricting keratinocyte motility. Additionally, IL-1β drives ECM remodeling through p38 MAPK pathway activation, which upregulates MMP2 and MMP9 while downregulating TIMP1 and TIMP2 [54]. Long-term NLRP3 inflammasome activation also slows cell proliferation and migration throughout the healing process by increasing IL-1β secretion [55]. Together, these effects underscore how disrupted cellular dynamics are central to impaired wound repair and link to subsequent pathological features, such as impaired angiogenesis and altered ECM remodeling.

Impaired angiogenesis

Pro-inflammatory cytokines like TNF-α and IL-1β disrupt new blood vessel formation in DFUs. They induce more ROS and protease production, which degrade the ECM and destabilize new vessels [56]. Additionally, they suppress angiogenic growth factors, including VEGF and PDGF, which further decreases endothelial proliferation and vessel support [48]. These effects lead to hypoxia and reduce nutrient delivery to the wound, delaying healing. Excess pro-inflammatory cytokines turn the microenvironment anti-angiogenic. This imbalance blocks blood vessel formation and worsens tissue damage. TNF-α causes endothelial, keratinocyte, and fibroblast apoptosis, all crucial for healing and angiogenesis. Persistent IL-6 and IL-1β restrict endothelial cell migration and lower TGF-β, a key pro-angiogenic factor. Dominance of M1 macrophages and decreased transitions to M2 macrophages, which are essential for anti-inflammatory and pro-angiogenesis, also contribute to reduced angiogenesis. Further, the presence of more anti-angiogenic fibroblasts than pro-angiogenic types reduces angiogenesis and prevents wound healing in DFU [53, 57–60]. Studies show that boosting angiogenesis can improve DFU outcomes. For example, stem-cell-based therapies are promising [61]. Impaired angiogenesis keeps wounds chronically nonhealing by starving them of oxygen and nutrients. TGF-β signaling effect on angiogenesis in DFUs is complex and structure-dependent. For example, lower growth differentiation factor 10 (GDF-10), a TGF-β family member, inhibits TGF-β1/Smad3 signaling and impairs wound healing [62].

Altered extracellular matrix remodeling

In DFUs, cytokine imbalance leads to chronic inflammation. This stops proper ECM remodeling and leaves wounds non-healing. High pro-inflammatory cytokines, like TNF-α, boost MMPs that break down collagen and fibronectin excessively [60]. The result is poor formation of stable new tissue. DFU fibroblasts produce less fibronectin and collagen [58], so a functional provisional matrix cannot form. This matrix is vital for cell migration and tissue restoration. Even new ECM proteins are poorly organized. The ECM layer is dysfunctional, hindering cell attachment, proliferation, and healing [60]. Cells, especially fibroblasts, respond weakly to growth factors like TGF-β, which normally regulate ECM production. In DFUs, wound fibroblasts show a weak or abnormal response to these signaling molecules [63].

Reduced epithelialization in wound healing

Chronic inflammation causes delayed healing in DFUs by reducing epithelialization and creating a non-healing, hyper-inflammatory state [63]. Acute inflammation is needed for healing, but diabetes extends and disrupts this stage. Prolonged inflammation creates a cycle of tissue damage and blocks the proliferative phase, including re-epithelialization [52]. Persistently high inflammatory cytokines, such as TNF-α, directly impair keratinocyte migration needed for wound closure [60]. Long-term pro-inflammatory immune cells boost MMP production. Normally, MMPs help remodel the ECM. In DFUs, their higher activity breaks down vital proteins and growth factors for epithelial cells. Glucose also forms AGEs, which block cell communication and damage keratinocytes and fibroblasts. This further impairs epithelial cell movement, causing slow epithelialization and wound closure [64]. Diabetes-related vascular disease compounds the problem by lowering blood flow. This creates hypoxia, which deprives cells of oxygen and energy essential for healing.

Modulating cytokines

To regulate cytokine imbalance in DFUs, a shift is needed from a pro-inflammatory to a pro-regenerative state [65]. DFUs have high TNF-α, IL-1β, and IL-6, and low anti-inflammatory and growth cytokines. In chronic DFUs, M1 macrophage accumulates and inhibit healing. Clinical therapies are designed to lessen this state and switch from pro-inflammatory to reparative M2 macrophage that releases growth factors. Therapeutic strategies, therefore, aim not simply to suppress inflammation but to restore appropriate immune balance and timing, allowing transition toward an M2-dominant, pro-regenerative environment.

Sodium-glucose co-transporter 2 inhibitors

Sodium-glucose co-transporter 2 (SGLT2) inhibitors have benefits beyond their glycemic control properties in decreasing circulating TNF-α and IL-6, which decreases systemic pro-inflammatory markers for a more favorable wound environment [69]. The process leading to this anti-inflammatory effect is quite complicated. In addition to improving hyperglycemia, SGLT2 inhibitors are thought to drive the body into a state of ketosis, which then inhibits the NLRP3 inflammasome, a major initiator of IL-1β. Moreover, the medications can stimulate mitochondrial activity in endothelial cells and macrophages, thereby reducing oxidative stress and, subsequently, the production of pro-inflammatory cytokines. This scenario creates a less inflammatory environment throughout the body, which is no longer a candidate for chronic inflammation typical of DFU. Hence, the cellular processes necessary for repair are indirectly promoted. SGLT2 inhibitors have been proposed as a promising preventive and complementary strategy, as their multiple effects help address metabolic imbalance and inflammation simultaneously.

Biologic agents

The literature shows that biologics used to manage cytokines, including TNF-α inhibitors (infliximab, etanercept) and IL-1 receptor antagonists (anakinra), enhance angiogenic processes, fibroblast function, and collagen deposition [70, 71]. The activity of these monoclonal antibodies and receptor antagonists is highly selective, as they target directly the cytokines responsible for the inflammatory phase and the death of cells related to healing. Take, for example, TNF-α inhibitors: the fibroblasts would then be responsive to growth factors, and the keratinocytes would not undergo TNFα-mediated apoptosis. Thus, re-epithelialization would continue. The increase in collagen deposition can be attributed to the liberation of fibroblasts from the inhibitory, catabolic state characteristic of the cytokine-rich environment [71]. On the other hand, Singh et al. [72], in their review, warn that this targeted immunosuppression, while very effective, will require the strictest patient selection and infection monitoring, because the very cytokines being blocked (for instance, TNF-α) are also vital for the body to be able to mount an effective immune response against pathogens.

Biologics in DFU infections involve using naturally derived or engineered substances (like growth factors, blood derivatives, or natural compounds) to speed healing, fight microbes, and reduce inflammation, often targeting persistent issues like bacterial biofilms and excessive oxidative stress that standard treatments miss, with approaches including autologous blood products, growth factor gels (like becaplermin), and novel topical agents that modulate inflammation and promote tissue regeneration. Recombinant human growth factors, such as PDGF (e.g., regranex), are delivered in a hydrogel to promote healing [73, 74]. Agents like WF10 (immunokine) include biologics (anti-TNF, anti-cytokines like IL-1, IL-12/23), small molecules [nonsteroidal anti-inflammatory drugs (NSAIDs), steroids, statins], and newer gene therapies (IL-10 gene therapy) that help regulate chronic inflammation [75, 76]. Though there is no direct evidence that these agents help in DFU healing, their role in other autoimmune diseases gives hope.

Treg-based interventions

In DFU, the underlying cause of chronic inflammation is due to poor activity of Tregs. Pre-clinical studies suggest that cellular transfer or pharmacological stimulation to restore Treg activity can increase granulation tissue to heal wounds faster [47]. Tregs are the primary regulators of immune balance, and their impairment in diabetes leads to the activation of both T cells and macrophages, resulting in persistent inflammation that is difficult to resolve. Treatments aim to restore balance in the immune system by either supplying the patient with Tregs that have been expanded and tailored to the patient’s specific needs or by using drugs such as low-dose IL-2, which enhances the Treg population already present in the patient [77]. The significant increase in granulation tissue brought on by Tregs can be linked to the ability of this cell population to produce different factors, one of which is amphiregulin, while at the same time inhibiting the production of IFN-γ and other cytokines that are harmful to the growth of fibroblasts and endothelial cells [77]. Therefore, Treg-oriented therapy appears to be a major strategy that can not only suppress the inflammation but also invigorate the proliferative phase, thus assisting the healing process.

Novel anti-inflammatory agents

New approaches to treat inflammation are being developed while targeting inflammation more precisely. Decreasing IL-1β release through NLRP3 inflammasome inhibitors, antioxidants to neutralize ROS, and growth factor-modulating agents through nanotechnology-based dressings can improve wound healing [45]. Having the ability to target the immune system without or less systemic immunosuppression will leave these therapies as a favorable option. Innovative strategies for anti-inflammatory treatments are being researched that target the site of inflammation with precision [78]. Among the possible approaches are the inhibition of IL-1β release with NLRP3 inflammasome inhibitors, neutralization of oxidative damage with antioxidants, and the use of growth factor-modulating agents via nanotech-based dressings [78]. The NLRP3 inflammasome, a major intracellular sensor in chronic wounds, is triggered by damage-associated molecular proteins (DAMPs), and its blockade controls the potent IL-1β family of cytokines at the earliest stage [79]. At the same time, new antioxidant strategies take the process beyond simple antioxidant action; they can include the selective distribution of substances such as N-acetylcysteine to potentially interfere with the ROS-NF-κB inflammatory feedback loop. The introduction of nanotechnology in the form of dressings is a major milestone, as it not only provides the prolonged and site-specific release of these new agents (such as inflammasome inhibitors, growth factors, or antioxidants) at the wound site, thus maximizing the therapeutic effect while reducing the systemic exposure [80]. Such a precise, multi-targeted method, as the study suggests, not only selectively influences the immune system without the broad-spectrum immunosuppression side effects associated with regular biologics but is also a highly preferred future option [79].