The long-term goal of this research is to design immunologic interventions to prevent onchocercal interstitial keratitis. We have used a murine model to study the role of cytokines in this disease. BALB/c mice sensitized repeatedly with soluble Ags of O. volvulus (OvAg) develop a strong Th2 response and keratitis following intrastromal challenge. Corneal pathology is dependent on Ag-specific T cells since athymic nu/nu mice do not develop these lesions, whereas reconstitution with spleen cells from OvAg-sensitized euthymic mice results in corneal pathology. Administration of IL-12 to helminth-sensitized mice enhances Th1 reactivity, concomitant with suppression of established Th2 responses. Examination of several recombinant Onchocerca Ags that are potential vaccine candidates indicates that Ov33 and RAL2 recall Th2 responses by lymphoid cells from OvAg-sensitized mice.
The specific aims are to: 1. Define the role of Th2 CD4+ cells and cytokines in the pathogenesis of onchocercal keratitis. The pattern of cytokine mRNAs and their cellular sources in the corneal stroma of mice with keratitis will be determined by RT-PCR. The causal role of Th2 cells will be ascertained by depletion of IL-4 in vivo and adoptive transfer of Ag- specific Th1 and Th2 cells. 2. Determine whether downregulation of established Th2 responses by counterregulatory cytokines inhibits development of interstitial keratitis. Prior to intrastromal challenge, mice with established Th2 responses to OvAg or recombinant Ag (Ov33 or RAL2) will be treated with rIL-12 or anti-IL-10 Ab to shift the balance of Th subset responses to Th1. 3. Examine whether vaccination with selected recombinant Ags combined with Th1-promoting cytokine IL-12 inhibits Th2-mediated corneal pathology. These experiments will determine whether establishment of strong Th1 responses to Ov33 or RAL2 prior to exposure to OvAg prevents development of keratitis. Results of these studies will contribute to the design of anti-pathology vaccines and cytokine-based therapy of onchocercal keratitis.
