Pancreatic autoantibodies and CD14+CD16+ monocytes subset are associated with the impairment of ß-cell function after simultaneous pancreas-kidney transplantation

Abstract

Pancreatic autoantibodies (AAb) has been associated with a worse pancreas graft survival after simultaneous pancreas-kidney transplantation (SPK). However, due to the variable time for AAb to become positive and the lack of early biomarkers suggesting such autoimmune activation, the mechanisms leading ß-cell destruction remain uncertain. The present study aimed to evaluate the association between post-transplant AAb and the functional impairment of the pancreatic ß-cell and also the association of such AAb with inflammation after SPK. In a longitudinal study, we analyzed the impact of post-transplant glutamic acid decarboxylase (GAD-65) and the insulinoma-associated autoantigen 2 (IA-2) AAb on pancreas graft function. Serum Hb1Ac and C-peptide (C-pep) were longitudinally compared between a group with positive posttransplant AAb (AAb+; n = 40) and another matched group with negative AAb (AAb-; n = 40) until the fifth year following seroconversion. In the cross-sectional analysis, we further evaluated the systemic signatures of inflammation by measuring pro-inflammatory CD14+CD16+ monocytes by flow-cytometry and interleukin 17-A serum levels in 38 SPK recipients and ten healthy controls. In the longitudinal study, patients with AAb+ showed higher levels of Hb1Ac (p<0.001) and lower C-pep levels (p<0.001) compared to those who remained AAb- throughout the follow-up. In the cross-sectional study, AAb+ patients showed a higher percentage of CD14+CD16+ monocytes compared with those with AAb- and the healthy controls (6.70±4.19% versus 4.0±1.84% and 3.44±0.93%; p = 0.026 and 0.009 respectively). Also, CD14+CD16+ monocytes correlated with Hb1Ac and C-pep serum levels. Multivariate logistic regression showed that posttransplant AAb+ was independently associated with a higher percentage of pro-inflammatory monocytes (adjusted-OR 1.59, 95%CI 1.05-2.40, p = 0.027). The group of patients with positive AAb also showed higher levels of IL17A as compared with the other groups (either healthy control or the negative AAb subjects). In conclusion, pancreatic AAb+ after SPK were not only associated with higher Hb1Ac and lower c-peptide serum levels but also with an increased percentage of CD14+CD16+ monocytes and higher levels of circulating IL17-A.

Fig 1

Glycated hemoglobin (A) and C-pep (B) serum levels among patients with positive and negative pancreatic AAb. The dark-dashed line represents positive AAb patients, and the continuous line represents AAb negative patients. I bar represents standard deviation. The number of patients at each time-point is depicted under x-axis. & p>0.05, * p<0.001, ^# p<0.01.

Fig 2

Distribution of CD14⁺CD16⁺ monocytes between the healthy controls and those with negative or positive AAb (A) and among different AAb types (B). I bar represents standard deviation.

Fig 3. Plots showing the correlations between glycated hemoglobin, c-peptide serum levels, and monocytes.

The continuous line represents the regression line. Correlation between the CD14⁺CD16⁺ monocytes and Hb1Ac levels (A) and c-Pep serum levels (B). Patients were stratified according to the positivity or negativity of pancreatic AAb. Among patients with negative AAb, Hb1Ac and C-Pep serum levels showed no correlation with the CD14⁺CD16⁺ monocytes (C and E). On the contrary, these correlations remained significant among those with positive AAb (D and F).

Fig 4. Plots showing IL-17A and IFN-y plasma values among five patients included.

(A) Patients with positive AAb showed higher levels of IL17A compared to those with negative pancreatic AAb and the healthy controls. (B) Plot showing IFNy among different groups.