CD4 and Keratoconjunctivitis sicca: Secondly, when the chemokine receptor CXCR3 (along with CCR5) expressed by Th1 cells binds to their specific ligands, such as INF-γ, they act as a central mediator to coordinate the localization of CD4+ T cells to the ocular surface to perform an immune response, causing dry eye occurrence [31].