Equis ISSN 2398-2977

Immunology: evaluation

Contributor(s): Cody Coyne, Mark Holmes, Prof Derek Knottenbelt, Nicola Menzies-Gow

Introduction

The immune system
  • A complex network of tissues and their secretions enables the body to reject foreign material such as infectious micro-organisms.
  • It is not fully understood in any species.
  • In the horse, a species for which considerably less research has been performed, there are a limited repertoire of tests and techniques that may be used to assess immune function.
  • The immune system contains non-specific and specific defense mechanisms.

Non-specific immunity

  • Provided by:
    • Physical barriers such as the skin, respiratory epithelium and gut wall.
    • Bacteriocidal and virocidal secretions such as the acid in the stomach.
    • Non-pathogenic commensal organisms such as those found on the surface of the skin and in the gut.
    • Phagocytes such as macrophages and polymorphs.
    • A subpopulation of lymphocytes known as NK ('natural killer') cells.
    • Interferon (antiviral properties).
    • Neutrophils.
    • Lysozyme (tears).

Specific immunity

  • Important aspect of the immune system.
  • Cells within the lymphoid system undergo a complex mechanism of gene re-arrangements to enable the immune system to recognize an enormous variety of foreign material.
  • A feature of the specific immune system is the ability of the immune system to remember previous encounters and mount a more energetic response when exposed to the same material on a subsequent occasion, eg memory cells.
  • This facility is exploited by vaccination strategies that can be beneficial or detrimental to the animal's health when excessive, eg hypersensitivity reactions   Insect hypersensitivity  .

Cellular immunity

  • Facilitate in T-lymphocytes by antigen-specific receptors expressed on their surface.
  • Particularly important in the defense against viruses and neoplasia.

Humoral immunity

  • Results from the secretion of antibody by B-lymphocytes.
  • Important component in the defense against bacterial infections and some viral conditions.

Clinical evaluation

  • There is a lack of tools or tests that are of clinical use.

In all but a few specific disease conditions an evaluation of the immune system in diseased animal will only confirm that which is already apparent, ie that the patient is unable to eliminate infections.

  • Immunodeficiencies:
    • Innate (primary): caused by a gene defect or failure of passive transfer.
    • Acquired (secondary): such as the immunosuppression associated with EHV-1 infection   Equine herpesvirus  or steroid administration.
  • Immunosuppression or immunodeficiency   →   reduced ability to resist infectious diseases   →  
    • Increase in pathological injury induced by a given particular pathogen.
    • Increased duration of disease.
    • Signs of disease caused by organisms that don't normally cause disease (opportunistic infection).
  • Any of these findings is an indication of a general functional immunodeficiency.
  • Although this offers no specific diagnostic value it indicates a poor prognosis.

Humoral immunity

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Cellular immunity

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Further Reading

Publications

Refereed papers
  • Recent references fromPubMedandVetMedResource.
  • Desmettre P (1999)Diagnosis and prevention of equine infectious diseases - present status, potential and challenges for the future. Adv Vet Med41, 359-377PubMed.


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