Autoimmune Responses

BREAKDOWN OF IMMUNE TOLERENCE TO SELF ANTIGEN (AUTOIMMUNITY)

Antigen hidden or sequestrated in cells or tissues

  • Some body proteins remain hidden or sequestrated from immunologically competent cells. So, they are not recognized as ‘self’ by the immune system.
  • When such protein escape into the circulation (due to trauma or infection), they behave as antigens, induce immune response and produce tissue damage.
  • Examples:
    • Lens protein: usually isolated or sequestrated from immune system
      during development. Due to trauma to the eye, lens protein may escape into circulation, produce autoantibody and cause immunologic damage to the eye (sympathetic ophthalmia).
    • Hepatitis: In chronic hepatiis in dogs, autoantibodies are produced against liver membrane proteins.

Antigen formed by molecular changes

  • Body tissues or cells undergo antigenic alteration due to physical, chemical or biological influences. Such neoantigen elicit immune response.
  • Examples:
  • Immunoconglutinins(IKs): IKs are antoantobodies produced against complement components like C2, C3 and C4. The new epitopes are exposed during complement activation and form IKs. The lecel of IKs in serum reflects the amount of complement activation.

Molecular Mimicry (Cross reacting antigen)

  • Molecular mimicry or sharing of epitopes between an infectious agents or parasites and body tissue specific antigen results in autoimmunity and tissue damage.
  • Example: Trypanosoma cruzi contain antigen that cross react with mammalian neurons and heart muscle results in nervous and heart disease.
Last modified: Tuesday, 17 April 2012, 10:04 AM