Exploiting Treg Plasticity and Immune Cell Metabolism to Control Stromal Keratitis

Ocular infections with Herpes Simplex virus (HSV) can have damaging consequences one of which is the loss of vision due to a chronic inflammatory reaction. T cells of the Th1 subset appear to be the main orchestrators of the inflammatory reaction. Certain components of the host immunity help to suppress the severity of lesions. My research focuses on one such protective component - CD4 regulatory T cells (Treg). We showed that Treg can initially function to suppress lesion development but this function can be lost and become pro-inflammatory. This provided the challenge of why this so-called plasticity occurred and how might it be prevented from developing. I was able to show that inhibiting the epigenetic modification occurring within the Foxp3 gene curbed the Treg plasticity. This reversal of plasticity was sufficient to enhance the control of SK lesion severity.Another focus of my research was to find ways to rebalance immune subsets in SK lesions. We pioneered a new approach which exploited different metabolic requirements for the pro-inflammatory and regulatory T cells in lesions. Pro-inflammatory T cells such as Th1 use glucose for its function, whereas Treg rely on fatty acid oxidation and to a lesser extent on glucose. Using 2-Deoxyglucose which inhibits glucose utilization, the pro-inflammatory Th1 were affected but not Treg thereby reducing lesion severity. It was important not to impair glucose utilization when replicating virus was present since this could result in virus spreading to the brain to cause encephalitis.We also evaluated if Treg were involved in repairing SK lesions. We could show that Treg within the cornea made a tissue repair molecule called Amphiregulin peaking during lesion development. This expression of Amphiregulin was partly dependent on the cytokines IL-18 and IL-12 which acted together to induce the expression of Amphiregulin. Moreover, enhancing the levels of IL-18 in the cornea using an expression plasmid helped resolve SK lesion severity, an effect which correlated with increased Amphiregulin expression by Treg.In conclusion, my studies revealed several innovative approaches which might be moved to the clinic to help minimize the consequence of an important cause of human blindness.