CD40 Expression and its Association with Low-grade Inflammation in a Greek Population of Type 1 Diabetic Juveniles: Evidence for Differences in CD40 mRNA Isoforms Expressed by Peripheral Blood Mononuclear Cells

Background: CD40 signalling has been associated with the pathogenesis of autoimmune diseases and diseases with low-grade chronic inflammation. Objective: To investigate, early in the course of type 1 diabetes (T1DM) patients, the expression of CD40 system components, as well as to explore the association of plasma and urine concentrations of CD40 with known inflammatory markers in T1DM. Methods: Plasma, urine and peripheral blood mononuclear cells (PBMCs) from 70 T1DM patients without clinically detected chronic complications and 40 healthy controls (HCs) were examined using ELISA, western-blot, semi-quantitative RT-PCR and DNA-sequencing. Results: Patients had significantly higher plasma soluble CD40 (sCD40) levels associated with higher Interleukin-6 (IL-6), matrix metalloproteinase-9 (MMP-9) and CRP levels compared with healthy controls. This difference was also evident between poorly and well-controlled diabetic patients. The elevated plasma sCD40 levels do not appear to be due to diminished renal excretion since sCD40 concentrations in the urine were also elevated, suggesting an increased CD40 production. An upregulation of PBMCs' CD40 was evident in T1DM patients associated with higher sCD40, IL-6 and CRP levels. Furthermore, the main CD40 isoform (isoform-I) was solely expressed in poorly controlled diabetics' PBMCs, who also demonstrated cellular CD40 upregulation, higher plasma CD40, CRP, IL-6 and MMP-9 levels compared with the well-controlled diabetics and the control group, who co-expressed type I and II isoforms. Conclusions: Homeostatic dysregulation of CD40 and its association with inflammatory markers in T1DM patients, especially in those with poor glycaemic control, implies a pathophysiological role of CD40 in the low-grade inflammatory process in T1DM.