The Th1/Th2 paradigm in ocular allergy

Purpose of review: The paradigm that diseases are either Th1 mediated or Th2 mediated has recently been challenged in a number of classical ocular diseases. The objective of this article is to highlight the importance of understanding the exact mechanisms of Th1 and Th2 cells in the pathology of ocular allergy. Recent findings: Current research of Th1 and Th2 cytokines in an animal model of ocular allergy demonstrates the intricate complex regulation by both subsets of cytokines of the disease process. Th2 prone BALB/c wild type mice sensitized and topically challenged with short ragweed for seven consecutive days (multi-hit) developed a sustained, chronic conjunctival inflammation. Significantly, IFN-γ knockout mice in the multi-hit antigen challenge model had a reduced conjunctival cellular infiltrate. Evaluation of adhesion molecules that actively regulate cellular infiltration into the conjunctiva revealed a lack of vascular cell adhesion molecule-1 in multi-hit antigen challenged IFN-γ knockout mice. Summary: Recent ocular allergy studies question the Th1/Th2 paradigm. These studies encourage further understanding of the intricate interactions of Th1 and Th2 cytokines in ocular inflammatory disease. The following components of Th1 and Th2 cells in the development of chronic inflammation associated with allergic conjunctivitis will be discussed: T helper subsets Th1 and Th2 in ocular inflammation, activation of T cells in the lymph node, and the role of IFN-γ as the endothelium gatekeeper in the pathology of Th2-mediated allergic conjunctivitis.