Type 1 diabetes and cytokines: clinical opportunities

Type 1 diabetes, like all autoimmune diseases, is characterized by dysregulated pro-inflammatory and anti-inflammatory cytokines. Recent studies that reveal the dynamics suggest opportunities for therapy. The authors of a paper recently published in Clinical Immunology state:

"Therapeutic targeting of proinflammatory cytokines is clinically beneficial in several autoimmune disorders. Several of these cytokines are directly implicated in the pathogenesis of type 1 diabetes, suggesting opportunities for design of clinical trials in type 1 diabetes that incorporate selective cytokine blockade as a component of preventative or interventional immunotherapy."

They focused specifically on the cytokines IL-1, TNF, IL-12, IL-23, and IL-6...

"...towards a goal of using cytokine inhibition as a therapeutic platform to establish an in vivo milieu suitable for modulating the immune response in T1D."

Two studies published in Diabetes Metabolism Research and Reviews shed light on cytokine changes in the progression from latent to active type 1 diabetes in children. The authors of the earlier paper state:

"Type 1 diabetes (T1D) is suggested to be of T-helper (Th)1-like origin. However, recent reports indicate a diminished interferon (IFN)-γ secretion at the onset of the disease. We hypothesize that there is a discrepancy in subsets of Th-cells between children with a high risk of developing T1D, children newly diagnosed with T1D and healthy children."

They examined peripheral blood mononuclear cells (PBMC) in three groups of children with the HLA-risk gene DQB1*0302 or DQB1*0201 and DQA1*0501--those who were at high risk for type 1 diabetes because predictive islet cells antibodies [ICA] were present, those newly diagnosed TD1, and healthy children who had the risk genes but weren't expressing them (no autoantibodies). They assayed an array of cytokines: Th1- (IFN-γ, tumour necrosis factor [TNF]-β, interleukin [IL]-2), Th2- (IL-4,-5,-13), Th3- (transforming growth factor [TGF-β], IL-10) and inflammatory associated cytokines (TNF-α, IL-1α,-6) and chemokines (monocyte chemoattractant protein [MCP]-1,-2,-3, Monokine unregulated by IFN-γ [MIG], Regulated on Activation, Normal T-cell Expressed and Secreted [RANTES], IL-7,-8,-15). Their data documented a change in cytokine progression:

"The Th1 cytokines IFN-γ and TNF-β, secreted both spontaneously and by GAD65- and mitogen stimulation, were seen to a higher extent in high-risk children than in children newly diagnosed with T1D. In contrast, TNF-α and IL-6, classified as inflammatory cytokines, the chemokines RANTES, MCP-1 and IL-7 as well as the Th3 cytokines TGF-β and IL-10 were elevated in T1D children compared to high-risk children."

This shows an interesting shift implying that pro-inflammatory cytokines organize differently in the latent and active phases, and that the latter also has increased, presumably compensatory, anti-inflammatory activity (TGF-β and IL-10). The authors conclude:

"High Th-1 cytokines were observed in children with high risk of developing TID, whereas in children newly diagnosed with T1D Th3 cytokines, inflammatory cytokines and chemokines were increased. Thus, an inverse relation between Th1-like cells and markers of inflammation was shown between children with high risk and those newly diagnosed with T1D."

A subsequent study published in the same journal that also examined similar cytokine profiles in normal, high risk and T1D active children documented a burst of inflammatory activity early in the disease along with compensatory anti-inflammatory Th3 cytokines:

"High-risk children showed a dominant Th1-associated profile with high spontaneous and GAD65-induced secretion..In contrast, newly diagnosed T1D children showed a pronounced Th3-associated cytokine profile as well as a burst of inflammatory cytokines and chemokines secreted both spontaneously and by GAD65 and PHA stimulation...A dominant Th1-associated immune profile was observed during the pre-diabetic phase. This Th1 dominance, however, diminished in favour of a temporary increase in a Th3-associated and inflammatory immune profile at the onset of disease."

An important study published in Diabetologia investigated cytokine activity in adults with both active and latent autoimmune diabetes (LADA), and found in addition pro-inflammatory cytokine activity in type 2 diabetes as well. The authors state:

"Systemic pro- and anti-inflammatory cytokines are associated with both type 1 and type 2 diabetes, while their role in latent autoimmune diabetes in adults (LADA) is unclear. Therefore, we compared cytokine concentrations in patients with LADA, type 1 or type 2 diabetes and healthy individuals to test the hypothesis that differences of cytokine concentrations between all groups are attributable to diabetes type and BMI."

They measured the pro-inflammatory cytokines IL-6 and TNF-α, and the anti-inflammatory cytokines IL-1 receptor antagonist (IL-1RA) and IL-10 in 90 subjects with active type 1 diabetes, 61 adults with latent autoimmune diabetes (LADA; predictive antibodies), 465 with type 2 diabetes and 41 normal controls while adjusting for BMI, sex, age, blood pressure and diabetes duration. They found that LADA and active type 1 in adults had a similar cytokine profile, while the type 2 diabetes subjects had their own pro-inflammatory mix:

"Patients with type 2 diabetes had higher concentrations of systemic IL-1RA, IL-6 and TNF-α cytokines than patients with either LADA or type 1 diabetes (p < 0.0001 for all differences). Cytokine concentrations in controls were lower than those in all diabetes types (p < 0.04). Increased BMI was positively associated with higher systemic cytokine concentrations in all diabetes types (p < 0.0001). Despite the association of cytokines with anthropometric data, differences between diabetes forms persisted also after adjusting analysis for the confounders BMI, age, sex, disease duration and blood pressure."

Clinicians take note: this is further evidence that increases in BMI are associated with increased inflammation. The authors conclude:

"Although body mass associates positively with pro- and anti-inflammatory cytokine levels, patients with type 2 diabetes have higher cytokine levels independent of the prevailing BMI. LADA and type 1 diabetes could not be distinguished by systemic cytokines."

The foregoing evidence was updated in a paper just published in the journal Diabetes Research and Clinical Pracitice looked into how the immune profile progresses from pre-diabetes to full blown T1D by investigating...

"...the composition and possible changes of the immunological profile, spontaneously and following stimulation with the autoantigens GAD65, and HSP60, at high-risk and T1D onset and further to 8 months post diagnosis."

To do so they assayed cytokines (IL-1β, -6, -7, -10, -13, -17, IFN-γ and TNF-α) and chemokines (CCL2, -3, -4, -5 and CXCL10) associated with Th1, Th2, Tr1 and inflammatory cells and markers associated with regulatory T-cells in 25 children approximately four days and 8 months after diagnosis of T1D, 15 first-degree relatives of T1D patients with a high risk of developing T1D, and 16 healthy children as controls. They too saw differences in these three groups:

"High-risk individuals differed in immunity from that seen in healthy and T1D children. High-risk individuals had a low TNF-α response and fewer responders from mitogen exposure as well as low spontaneous secretions of IL-13 compared to healthy children. High-risk individuals that later developed T1D, had a lower FOXP3 and CTLA-4 mRNA expression [anti-inflammaotry], following stimulation with GAD65, in combination with higher secretion of the pro-inflammatory chemokine CCL4."

The authors conclude:

"Changes in immunity seen in individuals with high risk of developing T1D points to alterations/actions in the immune system already early in the pre-diabetic phase."

And for clinicians actively involved in managing T1D another study published recently Diabetologia illustrates some nuances of cytokine activity associated with the relative preservation of pancreatic beta cell function:

"Cytokines may promote or inhibit disease progression in type 1 diabetes. We investigated whether systemic proinflammatory, anti-inflammatory and regulatory cytokines associated differently with fasting and meal-stimulated beta cell function in patients with longer term type 1 diabetes."

They gave a standardized liquid mixed meal test (MMT) to 118 subjects with type 1 diabetes. 5 minutes before and 120 minutes later they measured proinflammatory (IL-6, TNF-α), anti-inflammatory (IL-1 receptor antagonist [IL-1RA]) and regulatory (IL-10, TGF-β1–3) cytokines. They also measured C-peptide, and naturally took into consideration sex, age, duration of diabetes, BMI, HbA1c and fasting blood glucose. It appears that the presence of more functional beta cells made that much more of a target for pro-inflammatory cytokines:

"High fasting systemic concentrations of the proinflammatory cytokines IL-6 and TNF-α were associated with increased fasting and stimulated C-peptide concentrations even after adjustment for confounders (p < 0.03). Interestingly, increased concentrations of anti-inflammatory/regulatory IL-1RA, IL-10, TGF-β1 and TGF-β2 were associated with lower fasting and stimulated C-peptide levels (p < 0.04), losing significance on adjustment for anthropometric variables. During the MMT, circulating concentrations of IL-6 and TNF-α increased (p < 0.001) while those of IL-10 and TGF-β1 decreased (p < 0.02) and IL-1RA and TGF-β2 remained unchanged."

Apparently the meal stimulated more inflammatory activity. Here's what the authors made of their findings which have important clinical implications:

"The association between better preserved beta cell function in longer term type 1 diabetes and increased systemic proinflammatory cytokines and decreased anti-inflammatory and regulatory cytokines is suggestive of ongoing inflammatory disease activity that might be perpetuated by the remaining beta cells. These findings should be considered when designing immune intervention studies aimed at patients with longer term type 1 diabetes and residual beta cell function."

What does all this mean for the practitioner involved in the treatment of type 1 diabetes, espeically now that we have therapies that can modulate cytokine acitivity?

• There is still a lot to be learned, but patterns of pro- and anti-inflammatory activity that lend themselves to treatment strategies are emerging.
• Clinicians should be alert to the latent ('silent', or 'reactive, pre-disease) stage of type 1 diabetes and their predictive antibodies and craft treatment plans accordingly.