Local antigen-presenting cells and restimulation of T cells during uveitis

Abstract

Purpose : Understanding the function of major histocompatibility complex class II positive (MHC II⁺) antigen-presenting cells (APCs) is critical in understanding the pathogenesis of autoimmune uveitis. We previously showed that MHC II⁺ microglia are not required for the systemic induction of uveitic-specific CD4⁺ T cells. In the current study, we determined which of the local MHC II⁺ APCs, either CD11c⁺ dendritic cells (DCs) and/or resident retinal CD11c⁺ P2ry12⁺ microglia, are important in expanding inflammation within the retina. We hypothesize that resident local microglia and not DCs are primarily responsible for the expansion of uveitis.

Methods : Two experimental autoimmune uveitis (EAU) models were used, (i) conventional EAU where C57BL/6 mice are directly immunized with IRBP, and (ii) adoptive transfer EAU in which donor uveitic T cells (14 days post-IRBP immunization) are injected i.p. into recipients. Clinical score was determined by the standard method. FACS analysis determined MHC II expression on microglia (P2ry12) and DCs (CD11c and CD45). We used the Cre-lox system to specifically knock-down MHC II on DCs or microglia. WT uveitic donor T cells were adoptively transferred into (i) recipient mice that lacked MHC II⁺ on CD11c⁺ DCs (MHC II^fl/fl CD11c^Cre/0), Neg. control (MHC II^fl/fl CD11c^+/0), or (ii) tamoxifen-treated recipient mice that lacked MHC II⁺ on P2ry12⁺ microglia (MHC II^fl/fl P2ry12^CreER/+ mice), Neg, control (MHC II^fl/fl P2ry12^+/+).

Results : At 10 days following induction of EAU, two distinct populations of MHC II⁺ cells are detected in the retina; CD11c⁺ P2ry12⁺ microglia (23.5±4.6%) and CD11c⁺ P2ry12^Neg DCs (60.1±7.1%). Using the adoptive transfer model of EAU, we demonstrated that knock-down of MHC II on CD11c⁺ dendritic cells in recipient mice had no effect on the severity of uveitis (max clinical score: 2.3±0.1 (MHC II^fl/fl CD11c^cre/0) vs 2.0±0.2 (control)). By contrast, knock-down of MHC II⁺ on CD11c⁺ P2ry12⁺ microglia reduced the severity of uveitis (max clinical score: 1.1±0.1 (MHC II^fl/fl P2ry12^cre/ERT) vs 2.0±0.1 (control)). Importantly, the frequency of MHC II⁺ P2ry12⁺ microglia directly correlated and the severity of uveitis (r=0.97).

Conclusions : Our data indicate that MHC II⁺ retinal microglia and not CD11c⁺ dendritic cells function as local APCs that exacerbate uveitis. Thus, reducing uveitis may be achieved by targeting MHC II⁺ microglia within the retina.

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.