IL17A and granulomatosis with polyangiitis: Zhao and colleagues studied the immunological process involved in the development of Mooren ulcer and found a regulatory imbalance in a subset of the T-cell population, with a decline in the number of suppressor CD8 T-cells compared to CD4 T helper cells, while also finding that the peripheral cornea and surrounding conjunctival lymphatics are directly implicated in the immunopathogenesis of the disease process.[33] Th17 cells expressing IL-17 along with other cytokines such as IL-1, IL-6, IL-17, IL-23 play a critical role in the pathogenesis of PUK in patients with GPA.[34,35]