Background/Purpose:

In systemic lupus erythematosus (SLE), the dysregulated production of autoantibodies is a consequence of disrupted T cell homeostasis. Programmed death-1 (PD-1), a negative regulator in T cells, limits certain T cell-mediated immune responses. Increased PD-1 expression on T cells inhibits cell activation and proliferation and its blockade reinstates immune cell function. Our laboratory has shown that attenuated, but not absent, PD-1 signaling enables CD4⁺ regulatory T cells (T_reg) to survive and suppress helper T cells T_h and B cells. Gene array data have shown that attenuated PD-1 expression in T_reg down-regulates several members of the TNF receptor family, including OX40L. It has been reported that OX40L is up-regulated in immune cells from patients with autoimmune disease by promoting follicular helper and effector memory T cells, and suppressing T_reg proliferation. We hypothesize that one mechanism by which PD-1 sustains T_reg proliferation and suppressive function is by reducing OX40L expression on T_reg.

Methods:

We treated lupus-prone BWF₁ mice with a neutralizing Ab against PD-1 or control isotype-matched IgG intraperitoneally. OX40L, Foxp3 and PD-1 expression on T_reg from the spleens was measured by flow cytometry. T_reg were cocultured with unmanipulated CD4⁺CD25^– T_h and B cells, and cell proliferation/apoptosis of T_reg, T_h and B cells was measured with CFSE/Annexin V by flow cytometry. Cytokine production namely IFNγ (T_h1), IL-4 (T_h2), IL-17a (T_h17) and TGF-β (T_reg), and anti-dsDNA (B cells) in the culture media were measured by ELISA. To test the plasticity of these T_reg, we treated T_reg with agonistic vs antagonistic OX40L Ab in vitro, and set up the coculture experiments and determined cell proliferation and cytokine production as described above.

Results:

OX40L expression was lower in PD1^loT_reg from anti-PD1-treated mice when compared to PD1^hiT_reg from controls. OX40L^hiT_reg, irrespective to its Foxp3 expression, lost its ability to suppress T_h and B proliferation. PD1^loT_reg treated with agonistic OX40L had attenuated suppressive function: there was decreased production of TGF-β, increased proliferation of T_h (T_h1 predominant) and increased anti-DNA production. These T_reg also had increased apoptosis. Treating PD1^hiT_reg with antagonistic OX40L could not restore the suppressivity in T_reg.

Conclusion:

Effective induction of T_reg is associated with low expression of PD-1, which permits cells to survive and perform cell suppressive function. Attenuated PD-1 expression in T_reg reduces OX40L expression on T_reg, which helps restore the suppressive capacity and proliferation of T_reg. Increased OX40L expression overrides PD-1 signaling to deactivate and induce apoptosis in Foxp3⁺T_reg, but reduced OX40L expression cannot recover T_reg suppressivity when PD-1 signal is high. The suppressive function induced by low PD-1 expression is influenced by the intensity of OX40L expression. PD-1 and OX40L signaling most likely crosstalk to regulate the suppressive capacity and survival of T_reg to achieve peripheral tolerance in SLE.

« Back to 2018 ACR/ARHP Annual Meeting

ACR Meeting Abstracts - https://acrabstracts.org/abstract/pd-1-signaling-interferes-with-ox40l-to-alter-the-suppressive-function-and-proliferation-of-cd4-regulatory-t-cells-in-lupus-mice/