Severing corneal nerves induces CD11c+ contrasuppressor cells that disable T regulatory cells induced by either orthotopic corneal allografts or by injection of antigen into the anterior chamber.

Abstract

Purpose : Corneal allograft survival is due in large part to T regulatory cells (Tregs) that block immune rejection. The severing of corneal nerves which occurs during penetrating keratoplasty releases the neuropeptide substance P (SP) in both eyes. SP disables the T regulatory cells that are needed for the acceptance of future corneal allografts. This release of SP induces the generation of CD11c+ dendritic cells that act as contrasuppressor (CS) cells that disable Tregs generated either by corneal transplants or injecting antigens into the anterior chamber (AC). This study characterized CS cells that are induced by penetrating keratoplasty or by severing corneal nerves.

Methods : CS cells were induced by placing 2.0 mm circular incisions (trephining) into the central corneal epithelium of BALB/c mice. The following questions about CS cells were addressed. What is the minimum number of CS cells that block Treg activity? How long-lived are CS cells? Do CS cells directly kill Tregs? Do CS cells produce SP? Does SP disable or kill T regs? Will SP convert naïve CD11c+ DC into CS cells? Tregs were induced by either AC injection of ova antigens (ACAID) or by orthotopic corneal transplantation. Treg activity was assessed in vivo with a local adoptive transfer (LAT) assay.

Results : Adoptive transfer of as few as 1x10³ CD11c+ CS cells prevented the induction of ACAID, which persisted for >60 days. In vitro assays revealed that CD11c+ CS cells did not directly kill Tregs. CS cells could not be induced in SP knockout (KO) mice or in wild-type mice treated with the SP receptor antagonist, Spantide II. SP was needed for the expression contrasuppressive activity as CS cells exposed to Spantide II were unable to block T reg activity in a conventional LAT assay.

Conclusions : The transient release of SP during corneal nerve ablation induces the generation of long-lived (>60 days) CD11c+ CS cells that disable the Tregs induced via AC injection of antigen or by orthotopic corneal allografts. CS cells do not directly kill Tregs but exert their inhibitory effect by releasing SP, which in turn disables Tregs.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.