Background/Purpose: MRL/lpr mice develop a chronic inflammatory disease characterized by accumulation of CD4^–CD8^–B220⁺T cells mimicking human lupus; IL-23 driven IL-17 producing cell contribute to lupus severity in B6/lpr mice, an autoimmune model that is characterized by deficient Fas-mediated apoptosis but without the autoimmune genetic background of MRL/lpr. We previously reported that in MRL.lpr mice, administration of neutralizing IL-23Ab ameliorates lupus severity. The studies presented below sought to explain the profound effect IL-23 has on murine lupus pathogenesis.

Methods: T cells were extracted from the blood of patients who fulfilled at least 4 out of 11 ACR criteria for SLE. We generated MRL/lpr mice that lack the IL-23 receptor by backcrossing the MRL/lpr mouse with a B6.IL-23 receptor (IL23R) deficient mouse for 11 generations. Proteinuria was monitored at regular intervals. Spleens, kidneys and lymph nodes were harvested and used for flow cytometry and histology at different time points. ELISA was used for measurement of cytokines and dsDNA antibody levels in the serum.

Results: Genetic deletion of IL-23R in MRL/lpr mice attenuated lupus nephritis strikingly decreasing the accumulation of double negative T (DNT) cells in the kidneys (IL23R^+/+MRL/lpr vs. IL23R^-/-MRL/lpr: 8.38+/-1.76 x10⁴ cells vs. 2.00+/-0.37 x10⁴ cells, p<0.05). We observed a similar decrease of DNT accumulation in secondary lymphoid organs in IL23R deficient vs the IL23R sufficient mice. Using in vivo BrDU staining and in vitro proliferation experiments, we found that the decrease in the DNT cell population in the spleen and lymph nodes of IL23R^-/-MRL/lpr vs the IL23R^+/+ MRL/lpr mice was through 1. Decreased DNT proliferation (IL23R^+/+MRL/lpr vs. IL23R^-/-MRL/lpr: 4.61+/-0.83% vs. 1.26+/-0.33%). 2. Increased DNT cell death (IL23R^+/+MRL/lpr vs. IL23R^-/-MRL/lpr: 37.13+/- 2.21 % vs. 46.11+/-0.21%), and 3. Decreased conversion of CD4⁺ T cells into DNT upon stimulation (IL23R^+/+MRL/lpr vs. IL23R^-/-MRL/lpr vs. MRL/MPJ: 11.95+/-0.07% vs. 4.90+/- 0.42% (p<0.05) vs. 3.19+/-0.07% (p<0.05 compared to wild type). Moreover, T cells from IL-23R deficient animals had significantly increased IL-2, and reduced IL-17 production compared to wild type animals. In vitro incubation of MRL/lpr splenocytes with IL-23 not only promoted IL-17 production, as expected, but also downregulated IL-2 production (IL-2 in non-IL23 vs IL-23 treated: 281.67+/-16.26 vs. 151+/-47.03 pg/mL). Conversely, exogenous IL-2 reversed IL-23-induced IL-17 secretion from IL-23R^+/+ MRL/lpr lymphocytes indicating that IL-23 critically regulates the balance between IL-2 and IL-17 in lupus prone mice. Finally, ex vivo treatment of T cells from SLE patients with IL-23 increased the proportions of IL-17-producing T cells and DN T cells (non-IL23 vs IL-23 treated: 27.72+/- 14.41% vs. 47.85+/- 16.47%) while downregulating the production of IL-2 (non-IL23 vs IL-23 treated: 314+/- 198 vs. 220+/-131 pg/mL).

Conclusion: Our results show that IL-23 regulates the production of two pivotal cytokines in murine and human SLE while promoting the production of pro-inflammatory DNT cells, critically influencing the balance between pro and anti-inflammatory cytokines in lupus.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/il-23-promotes-the-generation-of-dnt-cells-and-shifts-the-balance-between-il-2-and-il-17-production-in-murine-and-human-sle/