Equis ISSN 2398-2977

Immune-mediated disease: overview

Contributor(s): Cody Coyne, Prof Derek Knottenbelt, Graham Munroe


  • Immune-mediated diseases are not rare in horses as a total group but its diagnosis is usually a challenge.
  • Cause: immune-mediated disease can either be primary (or autoimmune) in which antibodies or activated lymphocytes develop against normal body constituents or secondary (immune-mediated) in which the antigen is foreign to the body and may include drugs, bacteria and viruses, which stimulates an immunologic reaction that results in host tissue damage.
  • Signs: vary according to specific condition.
  • Diagnosis: serology, histopathology, hematology.
  • Treatment: glucocorticoid administration is the basis of treatment, as antihistamines show limited efficacy in horses.
  • Prognosis: generally poor.





  • Pemphigus foliaceus Pemphigus foliaceus is associated with the production of autoantibodies directed against surface proteins of the keratinocyte, which mediate intercellular adherence.
  • Pemphigus vulgaris is associated with anti-desmoglein 3 antibodies.
  • Antibodies are directed against the basement membrane in case of bullous pemphigoid Skin: bullous pemphigoid.
  • Erythema multiforme Erythema multiforme is believed to be an immunologically mediated disorder in which keratinocytes may be targeted specifically by killer lymphocytes.
  • In purpura hemorrhagica Purpura hemorrhagica, it is postulated that the streptococcal antigens precipitate an immunologic response by IgA antibodies.
  • Anaphylaxis Anaphylaxis is an immediate form of immune-mediated hypersensitivity initiated by the formation of antigen-antibody complexes.
  • Immune-mediated keratitis is thought to occur due to loss of immune tolerance which results in altered immunoreactivity to auto-antigens and possibly cross reaction between infectious agents and self-antigens.
  • There is inadequate absorption of colostral antibodies in cases of failure of passive transfer Foal: failure of passive transfer (IgG).
  • Failure to produce both functional B and T-lymphocytes in case of severe combined immunodeficiency Immunology: combined immunodeficiency.
  • Immune-mediated hemolytic anemia Anemia: immune-mediated occurs in association with neonatal isoerythrolysis Immunology: neonatal isoerythrolysis in which maternal alloantibodies present in the colostrum are ingested and absorbed by the foal. The alloantibodies are directed against surface antigen on the foal's erythrocytes, resulting in cell lysis, agglutination, or both. It also occurs in associated with equine infectious anemia, blood transfusion reaction and immune-mediated hemolytic disease (IMHD). IMHD can be primary (idiopathic) or secondary to neoplasia, eg lymphosarcoma, drug therapy, eg penicillin, or clostridial infection.
  • In EIA, immune complex deposition onto platelets results in clearance of virus and antibody coated platelets by hepatic Kupffer cells and splenic macrophages.
  • Polyneuritis equi is thought to be the result of a T-lymphocyte mediated immune response against myelin.


  • With purpura hemorrhagica Purpura hemorrhagica, clinical signs usually occur 2-4 weeks following a respiratory infection.


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Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Kalsow C M, Dubielzig R R & Dwyer A E (1999) Immunopathology of pineal glands from horses with uveitis. Invest Ophthalmol Visual Sci 40, 1611-1615 PubMed.
  • Geor R J, Clark E G, Haines D M & Napier P G (1990) Systemic lupus erythematosus in a filly. JAVMA 197, 1489-1492 PubMed.
  • Lumsden J M (1990) Suspected immune-mediated polysynovitis and serositis in a horse. Austr Vet J 67, 470-471 PubMed.
  • Galan J E & Timoney J F (1985) Immune complexes in purpura hemorrhagica of the horse contain IgA and M antigen of Streptococcus equi. J Immunol 135 (5), 3134-3137 PubMed.
  • Reef V B, Dyson S S & Beech J (1984) Lymphosarcoma and associated immune-mediated hemolytic anemia and thrombocytopenia in horses. JAVMA 184, 313-317 PubMed.