Phlyctenular keratoconjunctivitis is most commonly a result of which type of hypersensitivity reaction?

Phlyctenular keratoconjunctivitis is most commonly a result of which type of hypersensitivity reaction?

• A. Type 1
• B. Type 4
• C. Type 2
• D. Type 3

Answer: (B)

Phlyctenular keratoconjunctivitis is driven by a delayed-type hypersensitivity reaction. Sensitized T lymphocytes recognize bacterial antigens—often from Mycobacterium tuberculosis or Staphylococcus aureus—presented in the limbus and release cytokines that recruit and activate macrophages and other inflammatory cells. This T-cell–mediated inflammation produces the small nodular phlyctenule at the corneoscleral junction and the surrounding injection, and it develops after a delay following antigen exposure. That timing and mechanism align with Type IV hypersensitivity. In contrast, immediate IgE-driven responses describe Type I reactions (allergic with itching and rapid onset), antibody-mediated Type II reactions target specific cell-surface components, and Type III involves immune complex deposition—none of which fit the localized limbal nodules of PKC.

Phlyctenular keratoconjunctivitis is driven by a delayed-type hypersensitivity reaction. Sensitized T lymphocytes recognize bacterial antigens—often from Mycobacterium tuberculosis or Staphylococcus aureus—presented in the limbus and release cytokines that recruit and activate macrophages and other inflammatory cells. This T-cell–mediated inflammation produces the small nodular phlyctenule at the corneoscleral junction and the surrounding injection, and it develops after a delay following antigen exposure. That timing and mechanism align with Type IV hypersensitivity. In contrast, immediate IgE-driven responses describe Type I reactions (allergic with itching and rapid onset), antibody-mediated Type II reactions target specific cell-surface components, and Type III involves immune complex deposition—none of which fit the localized limbal nodules of PKC.