Characterization of proinsulin-specific regulatory T cells in type 1 diabetes at different ages of onset

Background: Regulatory T cells (Tregs) play an important role in maintaining tolerance to self-antigens. Defects in frequency and function of polyclonal Tregs have been reported in type 1 diabetes (T1D). However, the characteristics of islet-specific Tregs have not yet been determined in juvenile-onset T1D (JOT1D) or adult-onset T1D (AOT1D) subjects, distinguished by their age at onset of T1D.

Methods: In the current study, we analyzed the frequency and phenotype of proinsulin (PI)-specific Tregs and PI-specific effector T (Teff) cells in peripheral blood of JOT1D and AOT1D subjects. For this, peripheral blood mononuclear cells were stimulated with PI derived peptides for 72 hours and PI-specific Tregs and PI-specific Teff cells were identified and characterized using the combination of HLA class II TMRs, FOXP3, and CD45RA by flow cytometry.

Results: At first, we observed no significant difference in the frequency of polyclonal Tregs between the T1D and HC subjects. However, a significant positive correlation between age and frequency of polyclonal Tregs was observed among all the subjects (r=+0.35, p=0.04). Upon segregation of T1D subjects in the two groups, we observed that JOT1D and AOT1D subjects harbor comparable frequency of PI-specific Teff cells as well as PI-specific Tregs in their peripheral blood, although the frequency of polyclonal Tregs was significantly higher in AOT1D subjects (p=0.02). Further, a higher proportion of PI-specific Tregs (p=0.002), as well as PI-specific Teff cells (p=0.04), exhibited memory phenotype in both the JOT1D and AOT1D subjects. Lastly, we observed no significant difference in the expression of FOXP3 and IL-2 receptor on PI-specific Tregs in the JOT1D and AOT1D groups.

Conclusions: Chronic antigen presentation results in a distinct memory-like phenotype of PI-specific Tregs in all T1D subjects irrespective of the age of disease onset.