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Type IV Hypersensitivities definitions

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  • Type IV Hypersensitivity
    A delayed immune overreaction mediated by T cells, peaking 24-72 hours after antigen re-exposure, distinct from antibody-driven responses.
  • T Cell
    A lymphocyte responsible for mediating delayed hypersensitivity reactions and forming immune memory after antigen exposure.
  • Sensitization
    The initial immune process where T cells are primed by first antigen exposure, enabling a stronger response upon re-exposure.
  • Memory T Cell
    A long-lived lymphocyte formed after sensitization, enabling rapid and robust responses to previously encountered antigens.
  • Contact Dermatitis
    A red, itchy, inflamed skin rash resulting from T cell-mediated response to haptens after repeated contact.
  • Hapten
    A small molecule that becomes immunogenic only after binding to a host protein, triggering T cell-mediated reactions.
  • Patch Test
    A diagnostic method used to identify the specific substance causing allergic contact dermatitis by observing skin reactions.
  • Tuberculin Skin Test
    A screening procedure using purified protein derivative to detect immune memory of tuberculosis exposure, not active infection.
  • Purified Protein Derivative (PPD)
    A protein extract from Mycobacterium tuberculosis used in skin testing to assess prior immune exposure.
  • Induration
    A raised, red, and firm area on the skin indicating a positive delayed hypersensitivity reaction in tests like the tuberculin skin test.
  • Autoimmune Disorder
    A condition where the immune system attacks self antigens, sometimes triggered by T cell-mediated hypersensitivity.
  • Self Tolerance
    A mechanism preventing immune responses against the body's own antigens; its failure can lead to autoimmunity.
  • Cytokine
    A signaling molecule released by T cells that orchestrates inflammation and tissue changes during delayed hypersensitivity.
  • Adaptive Immunity
    A branch of the immune system involving memory and specificity, crucial for delayed T cell-mediated responses.
  • Mycobacterium tuberculosis
    The bacterium whose proteins are used in PPD testing to check for immune memory of tuberculosis exposure.