(#42) IL-17 is expressed in insulin-containing islets of donors with type 1 and type 2 diabetes

PRESENTED BY: Estefania Quesada-Masachs

Authors
First NameLast NameAffiliation/Institution
EstefaniaQuesada-MasachsLa Jolla Institute for Immunology
SakthiRajendranLa Jolla Institute for Immunology
SamuelZilbermanLa Jolla Institute for Immunology
MadeleineGrafLa Jolla Institute for Immunology
WilliamKiossesLa Jolla Institute for Immunology
TiffanyChuLa Jolla Institute for Immunology
MehdiBenkhalaLa Jolla Institute for Immunology
Jae-Hyun MasonLeeLa Jolla Institute for Immunology
Matthiasvon HerrathLa Jolla Institute for Immunology
 

Purpose

IL-17 is a pro-inflammatory cytokine, important in shaping host immune responses against pathogens. IL-17 is also attributed to cause tissue damage and chronic inflammation in autoimmune diseases such as psoriasis, rheumatoid arthritis, and multiple sclerosis. An increase in IL-17 secreting CD4+ T cells and Th17 cells were observed in pancreatic lymph nodes and peripheral blood of subjects with type 1 diabetes (T1D). However, it is not known whether IL-17 is expressed in human pancreata in healthy conditions and during T1D or T2D pathogenesis. Last year we reported increased IL-17 expression in islets of donors with Type 1 and Type 2 diabetes with alpha and beta cells being the major cellular source. Since then, we have stained more cases from every diagnosis group and evaluated infiltrating CD45+ lymphocytes contribution to the observed IL-17 expression in T1D and T2D donors.
 

Methods

IL-17, CD45, Insulin, and Glucagon antibodies were individually optimized in FFPE human tonsil and pancreas sections. 21 Human pancreatic FFPE tissues sections from non-diabetic (n=5), autoantibody positive (n=5), T1D (n=6) and T2D (n=5) donors were stained for IL-17, Insulin, and Glucagon. Consecutive sections from selected T2D (n=1), T1D (n=2), and non-diabetic (n=1) cases were stained for IL-17, CD45, and Insulin. Whole tissue sections were imaged using Zeiss AxioScan Z1 slide scanner. High resolution images of islets were acquired using LSM780 Confocal Microscopy system. Quantitative image analysis was performed through Zen Blue and ImageJ software to find percentage of positive area and colocalization data for each marker within islet areas.
 

Summary of Results

IL-17 signal found in islets of non-diabetic and auto-antibody positive cases, had a weak, sparse pattern accounting for an average of 2.4% and 4.6% of islet areas, respectively. In donors with T1D, insulin containing islets (ICIs) had a stronger expression of IL-17, accounting to an average of 7.8% of total islet area. Insulin-deficient islets (IDIs) from T1D donors had a lower IL-17 expression, similar to the level seen in islets from non-diabetic cases. IL-17 expression was highest in islets from T2D donors, accounting for an average of 14.9% of islet area. Much of the IL-17 production was accounted by either beta or alpha cells, while in many cases beta cells were the major source. In ICIs of T1D cases, 27.8% of the IL-17 expression was contributed by beta cells, while 16.9% was contributed by alpha cells. In the islets of T2D cases, 37.4% of the IL-17 expression was contributed by beta cells, while 33.5% was contributed by alpha cells. The proportion of beta cells expressing IL-17 was significantly higher in the T2D cases (31.6%) and T1D ICIs (16.5%) compared to the cases from other diagnosis groups. The proportion of alpha cells expressing IL-17 was significantly higher in the T2D cases (22.3%) compared to the other groups. Subsequent staining of consecutive sections with CD45, IL-17, and Insulin showed CD45 accounted for a very small percentage of the total islet area (between 0.19 to 1.1%) and almost none of the IL-17 expression was attributable to CD45+ infiltrating lymphocytes. CD45 only contributed 0.23% of the IL-17 expression in the T1D cases and 0.025% in the T2D case.
 

Conclusions

According to literature, expression of IL-17 is usually restricted to Th17, gamma delta T cells and some cell types of the innate immune system. Our finding that IL-17 can be expressed in islet cells of T1D or T2D is quite intriguing and could be a result of beta cell dysfunction induced by either metabolic or immune stress. Further mechanistic studies in human islets or human islet organoid models may be helpful to determine under which conditions IL-17 expression can be induced, at least in vitro, in human islets.