Ocular Immunology

Ocular Immune System - Eye's Tiny Defenders

• Immune Privilege: Eye's unique defense, limiting inflammation to protect vision. Key sites: anterior chamber, vitreous cavity, subretinal space.
• Cellular Army:
  • Antigen-Presenting Cells (APCs): Langerhans cells (cornea, conjunctiva), macrophages.
  • Lymphocytes: T-cells & B-cells.
  • Mast cells: Key in allergic reactions.
• Soluble Weapons:
  • Tears: Contain Secretory IgA (sIgA) - first line of defense, lysozyme.
  • Complement system, cytokines.
• Specialized Lymphoid Tissues:
  • Conjunctiva-Associated Lymphoid Tissue (CALT).
  • Lacrimal Gland Associated Lymphoid Tissue (LGALT).

⭐ Anterior Chamber Associated Immune Deviation (ACAID) is a vital mechanism of ocular immune privilege, inducing systemic tolerance to intraocular antigens via regulatory T-cells.

Immune Privilege - Eye's VIP Pass

The eye uniquely tolerates antigens without damaging inflammation, vital for vision. This "VIP pass" is a complex protective strategy.

• Key Mechanisms:
  • Barriers: Blood-ocular barriers (blood-aqueous & blood-retinal).
  • Alymphatic: Cornea, lens, vitreous lack lymphatic drainage.
  • Soluble Factors: Immunosuppressive TGF-β, α-MSH, FasL create an anti-inflammatory milieu.
  • ACAID: Anterior Chamber Associated Immune Deviation; antigens in AC induce systemic tolerance via regulatory T cells.

⭐ ACAID is a major reason for the high success (>90%) of initial corneal transplants, even without HLA matching.

Ocular Hypersensitivity - Allergic Eye Alarms

Ocular damage from immune overreaction. Classified by 📌 Gell & Coombs:

Key Immunopathologies & Tx - Rogue Cells & Remedies

• Uveitis: Uveal tract inflammation.
  • Types: Anterior, Intermediate, Posterior, Panuveitis.
  • Etiology: Infections, autoimmune (HLA-B27), trauma.
  • Tx: Corticosteroids, mydriatics, immunomodulators (Methotrexate).
• Sympathetic Ophthalmia: Bilateral granulomatous panuveitis post-trauma/surgery to one eye.
  • Autoimmune to uveal antigens.
  • Tx: Aggressive immunosuppression; enucleation of injured eye within 2 weeks may prevent.
• Ocular Cicatricial Pemphigoid (OCP): Autoimmune conjunctivitis causing scarring.
  • Type II HSR. Leads to symblepharon, blindness.
  • Tx: Systemic immunosuppressants (Dapsone, Cyclophosphamide).
• Mooren's Ulcer: Idiopathic peripheral ulcerative keratitis (PUK).
  • Painful, progressive. Autoimmune.
  • Tx: Steroids, immunosuppressants.

⭐ Sympathetic ophthalmia can occur weeks to decades after initial injury; early enucleation of a non-salvageable traumatized eye is key prevention if vision is lost in that eye within 14 days post-injury to prevent sensitization to self-antigens and subsequent attack on the fellow eye (sympathizing eye).

High‑Yield Points - ⚡ Biggest Takeaways

• Anterior Chamber Associated Immune Deviation (ACAID) is a key mechanism for ocular immune privilege.
• Sympathetic Ophthalmia: bilateral granulomatous uveitis post-trauma; T-cell mediated against retinal antigens.
• Type I hypersensitivity (IgE-mediated) is common in allergic conjunctivitis.
• Type IV hypersensitivity (cell-mediated) is involved in phlyctenular keratoconjunctivitis and contact dermatitis.
• Corneal graft rejection involves both cellular (T-lymphocytes) and humoral immune responses.
• Uveitis can be associated with systemic autoimmune diseases like Ankylosing Spondylitis (HLA-B27).
• Toll-like receptors (TLRs) on ocular surface cells recognize PAMPs, initiating innate immune responses.