Interleukine-23, but Not Interleukine-2, Promotes the Generation of Memory Th17 Cells in Dry Eye Disease

Abstract

Purpose : Chronic dry eye disease (DED) is mediated by memory T helper (Th) 17 cells. How a small fraction of effector Th17 cells escape apoptosis during the resolution phase and develop into long-term survival memory Th17 cells is unknown. This study investigated the mechanisms of generation of memory Th17 cells in DED.

Methods : Acute DED was induced by exposing C57BL/6 mice to desiccating stress in a controlled environment chamber for 14 days. Thereafter, they were housed in a standard environment with normal humidity for additional 7 days. Frequencies of memory Th17 cells (IL-17A⁺CD44^hiCD4⁺) and their expression (mean fluorescein intensity, MFI) of the IL-2 receptor (CD25) and IL-23 receptor (IL-23R) at days 14 and 21 were analyzed by flow cytometry. Expression levels of IL-2 and IL-23 in conjunctivae were quantified by real-time PCR. In addition, effector T cells (CD62L^-CD44^loCD4⁺) from the draining lymph nodes of acute DED mice were sorted and cultured in the presence of IL-23 (10ng/ml), IL-2 (50IU/ml), or IL-23 and IL-2 together for 48 hours, and then the frequencies of memory Th17 cells were assessed by flow cytometry.

Results : A significant memory Th17 population emerged at the ocular surface at day 14 (56% of total Th17) and persisted until day 21; this same population was not seen in draining lymph nodes until day 21. These ocular surface memory Th17 cells expressed a comparable level of IL-23R (MFI: 60.4 vs 59.3) but a much lower level of CD25 (MFI: 20.9 vs 60.2) compared with effector Th17 cells. As the disease abated, the level of IL-23 on the ocular surface was persistently high (3 to 4-fold increase from baseline, p < 0.05), while IL-2 declined to the baseline level. After 48 hours of culture of effector T cells, the frequencies of generated memory Th17 cells in the presence of IL-23 were 3-fold higher than those in the presence of IL-2 (p < 0.05) and 2-fold higher than those in the presence of IL-23 and IL-2 together (p < 0.05).

Conclusions : These findings indicate that sustained IL-23 and diminished IL-2 in the ocular surface environment during the disease resolution phase promote memory Th17 generation.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.