Lipoxin A₄ Regulates T Effector Cell Trafficking in Autoimmune Uveitis

Abstract

Purpose : Lipoxin A₄ (LXA₄) is a small endogenous signaling molecule that regulates leukocyte function and has anti-inflammatory and pro-resolution bioactions in acute inflammation. Despite an impressive body of work, the direct actions of LXA₄ on lymphocytes is not well characterized. Previously, we showed that LXA₄ treatment ameliorates autoimmune uveitis in mouse models. Here we identify a potential mechanism involved in the regulation of T cell responses by LXA₄.

Methods : Experimental autoimmune uveitis (EAU) was induced by active immunization with 150 µg IRBP_651-670 peptide emulsified in CFA of C57BL/6 WT and 5-LOX KO (Alox5^-/-) mice (a KO mouse which does not produce LXA₄). For T cell transfer, cells were harvested on day 11 from spleen and lymph nodes of EAU immunized donors and 10⁷ CD3 T cells were transferred intraperitoneally into TCRβ^-/- recipients. Three days later, recipients were immunized with IRBP_651-670 peptide. Eyes and lymph nodes were collected at peak inflammation for flow cytometry analyses. Antigen-specific T cell responses in vitro were analyzed by ³H thymidine incorporated proliferation assay. CD4 T cells were treated with LXA₄ in vitro for 24 hours and analyzed for CCR7 expression by flow cytometry to assess modulation of CCR7 expression by LXA₄. LXA₄ levels were measured in serum of uveitis patients using ELISA.

Results : LXA₄ appeared to inhibit the expression of CCR7, which should result in enhanced emigration of T cells from peripheral lymph nodes to tissues. Funduscopy scores and flow cytometry analyses showed that EAU-immunized Alox5^-/- mice had significantly more IFNγ producing ocular cell infiltrates (p=0.0057) in comparison to WT controls at peak inflammation. Similarly, TCRb KO recipients of Alox5^-/- T cells developed worse disease in comparison to recipients of WT T cells (p=0.0014). Interestingly, uveitis patient serum (n=36) had significantly higher levels of LXA₄ (p=0.03) in comparison to healthy subjects (n=35).

Conclusions : In mouse EAU models, LXA₄ attenuates uveitis by regulating expression of T cell trafficking molecules in the periphery, likely affecting the migration of pathogenic T cells to the eye. Additionally, we show the first evidence that the production of protective LXA₄ is upregulated in the serum of uveitis patients. Hence, regulation and therapeutic amplification of the endogenous LXA₄ pathway may be a potential approach to control the severity of T cell-driven diseases.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.