Skin: phytohemagglutinin test - T-lymphocyte function in Horses (Equis) | Vetlexicon
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Skin: phytohemagglutinin test – T-lymphocyte function

ISSN 2398-2977

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Overview

  • The test should be performed at, or at least, within 4 days of birth in foals suspected of having poor immunity.
  • The test can equally be performed in older horses - the value and implications of the test to the owner are less easily accepted at a later stage.

Sampling

Source of test material

  • This test can be performed in vitroon samples of blood collected into lithium heparin anticoagulant.

Quantity of test material

  • Send 10 ml LiHep blood to laboratory.

Quality control

Timing of test

  • The test should be performed at, or at least, within 4 days of birth in foals suspected of having poor immunity.

Tests

Methodologies

  • Aseptic preparation of a clipped area of skin on the side of the neck.
  • Measurement of skin thickness using accurate tuberculin testing or fat thickness calipers/slide.
  • Injection: 50 microg PHA in 0.05 ml phosphate buffered saline intradermally using 1 ml tuberculin/insulin syringe and a 25 g x 1 cm needle.
  • Using the same technique inject the same volume of phosphate buffered saline at adjacent site - this acts as a negative control.
  • Measure skin thickness at two sites after 24 h - some swelling is usually present in normal foals after 4 h.

Technique intrinsic limitations

  • An in vitrotest is not subject to the variations of an in vivosystem and both methods have advantages and disadvantages.

Result Data

Normal (reference) values

  • Positive results produce obvious lumps - usually 2-10 mm in skin thickness at the site.
  • 0.6 mm is negative and suggests failure of T-lymphocyte responses.
  • Negative results usually have no lump at all.
  • A few cases 'respond' to the negative control. This response should be subtracted from the test result.

Further Reading

Publications

Refereed papers