## Pathophysiology of Blood–Retinal Barrier Breakdown in Posterior Uveitis ### The Blood–Retinal Barrier (BRB) The BRB consists of: 1. **Inner BRB:** Tight junctions between retinal vascular endothelial cells 2. **Outer BRB:** Retinal pigment epithelium (RPE) tight junctions **Key Point:** TNF-α is the primary pro-inflammatory cytokine responsible for disruption of tight junctions and increased vascular permeability in posterior uveitis. ### Mechanism of BRB Breakdown ```mermaid flowchart TD A[Uveitic inflammation]:::outcome --> B[TNF-α, IL-6, IL-8 release]:::action B --> C[Upregulation of adhesion molecules<br/>ICAM-1, VCAM-1]:::action C --> D[Leukocyte infiltration]:::action D --> E[Tight junction disruption<br/>Occludin, claudins, ZO-1 degradation]:::action E --> F[BRB breakdown]:::outcome F --> G[Retinal edema, vitritis]:::outcome ``` **High-Yield:** TNF-α acts on endothelial cells to: - Increase expression of ICAM-1 and VCAM-1 (leukocyte adhesion molecules) - Promote production of matrix metalloproteinases (MMPs), which degrade tight junction proteins - Increase vascular permeability through NO and prostaglandin pathways ### Comparative Roles of Other Cytokines | Cytokine | Role in Uveitis | Effect on BRB | |----------|-----------------|---------------| | **TNF-α** | **Pro-inflammatory, primary mediator** | **Direct BRB disruption** | | IL-2 | T-cell proliferation and activation | Indirect (via TNF-α amplification) | | IFN-γ | Th1 response, macrophage activation | Indirect (enhances TNF-α) | | IL-10 | Anti-inflammatory, immunosuppressive | Protective (reduces BRB breakdown) | **Clinical Pearl:** Anti-TNF-α agents (infliximab, adalimumab) are highly effective in refractory uveitis, confirming TNF-α's central role in pathogenesis. **Mnemonic:** **TNF = Tight junction Necrosis Factor** — remember TNF-α as the primary disruptor of BRB integrity. [cite:Nussenblatt RL. Uveitis and Immunoinflammatory Disorders. 2010] 
Sign up free to access AI-powered MCQ practice with detailed explanations and adaptive learning.