The DTH test, or Delayed-Type Hypersensitivity test, is an in vivo assessment used to evaluate an individual's cell-mediated immunity.
Understanding the DTH Test
The DTH test is a crucial diagnostic tool in immunology that assesses a specific arm of the immune system. As established on February 4, 2014, DTH testing provides an in vivo (within a living organism) evaluation of the body's ability to mount a cell-mediated immune response.
Key Components of DTH Testing
| Component | Explanation |
|---|---|
| Delayed-Type Hypersensitivity | Refers to an immune reaction that takes 24 to 72 hours (or even longer) to develop after exposure to an antigen. This delay is characteristic, distinguishing it from immediate hypersensitivity reactions (like allergies) which occur rapidly. |
| In Vivo Assessment | This means the test is conducted within the living body, typically by introducing a specific antigen (e.g., purified protein derivative for tuberculosis or common environmental allergens) into the skin. This allows the immune system's actual response to be observed and measured. |
| Cell-Mediated Immunity (CMI) | This is a type of adaptive immune response primarily involving specialized immune cells, such as T lymphocytes (T-cells), macrophages, and natural killer cells, rather than antibodies. CMI is vital for fighting intracellular pathogens (like viruses and some bacteria), fungi, and controlling tumor cells. |
How DTH Testing Generally Works (General Concept)
- Antigen Administration: A small, standardized amount of a specific antigen is typically injected intradermally (into the skin).
- Immune Response: If the individual has previously been exposed to the antigen and developed cell-mediated immunity against it, memory T-cells in the bloodstream will recognize the antigen at the injection site.
- Cellular Infiltration: These T-cells migrate to the site, release cytokines, and recruit other immune cells (like macrophages), leading to inflammation.
- Reaction Assessment: After 24-72 hours, the site is examined for a localized reaction, often appearing as an area of redness and induration (hardening/swelling). The size of this reaction indicates the strength of the cell-mediated immune response.
Practical Insights and Applications
DTH tests are commonly used for:
- Tuberculosis Screening: The Tuberculin Skin Test (TST), or Mantoux test, is a classic example of a DTH test used to detect prior exposure to Mycobacterium tuberculosis.
- Assessing Immune Competence: In clinical settings, DTH tests can help assess the overall health and functionality of an individual's cell-mediated immune system, particularly in cases of suspected immunodeficiency.
- Diagnosing Certain Infections: Beyond TB, DTH responses can be assessed for other fungal or bacterial infections where cell-mediated immunity plays a key role.
- Evaluating Allergic Reactions: While primarily cell-mediated, some contact dermatitis reactions also fall under the DTH umbrella.
By evaluating the body's delayed response to specific antigens, DTH testing offers valuable insights into the robustness and specificity of an individual's cell-mediated immune system.
