In Vivo Measures of Immune Function
The delayed T-cell hypersensitivity (DTH) response is a widely used in vivo assay for assessing an individual's bacterial host defence capability. Suppression of the response signals a failure of one or more components of the host defence sys
tem. In this procedure, a series of antigens (ubiquitous antigens derived from bacterial and fungal products as well as 2,4-dinitrochlorobenzene) are injected intradermally in the forearm and the area of induration is measured at 24 and 48 h. The rationale is that Langerhans cells will present the cutaneously encountered antigens to activated or memory T cells. Anergy (loss of cutaneous hyper-sensitivity) to skin testing is associated with adverse outcome from infections, burns, or surgical trauma and has been used to predict postoperative complications as well as the severity of various types of malnutrition (protein energy, iron, zinc, and vitamins A, C and B6) [49, 50]. Because of large interindividual variation in the response, sequential testing in subjects might be a more valuable use of this technique. The assumption is that improvement in the DTH response represents an increased resistance to infection; a decrease in the response was reported to be strongly associated with sepsis and related mortality in intensive care or trauma patients [51]. Neither the sensitivity nor the value of the DTH response for measuring moderate changes in nutrient intake in healthy persons is clear. However, DTH response appears to have been used successfully in a study that evaluated the efficacy of a nutritional supplement in the elderly [6].
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