The Lewis triple response, named after Sir Thomas Lewis, is a simple yet profound illustration of the body's vascular and nerve-mediated reactions to a minor trauma. It provides valuable insights into the initial stages of inflammation.
The Three Phases of the Lewis Triple Response
1. The Red Line
Appearing within seconds along the path of the stroke, the red line is the first sign. It's caused by the immediate release of histamine and other chemical mediators from mast cells and basophils in the skin. Histamine dilates local capillaries, increasing blood flow and causing the visible redness.
2. The Flare
A wider, brighter red flush, the flare, spreads out from the red line. This phase involves an axon reflex: sensory nerve endings activated by the injury send signals that travel backward along the nerve, releasing neuropeptides like CGRP and substance P. These neuropeptides dilate nearby arterioles, creating the broader red flare.
3. The Wheal
The final phase is a raised, pale wheal developing around the red line. This swelling results from increased vascular permeability caused by histamine and other mediators. Protein-rich fluid leaks from post-capillary venules into the surrounding tissue, forming the visible edema.
The Mechanism Behind the Triple Response
The triple response is a coordinated event driven by inflammatory mediators and a local nerve reflex. For a detailed breakdown of the key steps, refer to {Link: Dr.Oracle https://droracle.ai/articles/42873/what-is-the-triple-response-of-lewis-also-known-as-the-lewis-triple-response}.
Clinical Significance and Related Conditions
Understanding the triple response is clinically important.
Dermatographism
Some individuals have a heightened triple response called dermatographism, or 'skin writing'. Even light strokes cause a pronounced, persistent wheal and flare, an exaggerated, often urticarial (hives) reaction.
Allergy Testing
The triple response principles are central to allergy testing. Introducing an allergen causes a histamine-mediated wheal and flare, helping assess allergic sensitivity.
Neurological Assessment
A diminished flare response can indicate neurological problems, suggesting a disruption of the local axon reflex. This can help evaluate sensory loss, such as in spinal cord injuries.
Comparison Table: Triple Response vs. General Inflammation
| Feature | Triple Response of Lewis | General Inflammatory Response |
|---|---|---|
| Timing | Immediate (seconds to minutes) | Starts rapidly but can persist for hours or days |
| Cause | Mechanical trauma or chemical mediators (histamine) | Wide range of triggers (infection, injury, irritants) |
| Components | Red line, flare, and wheal | Redness, heat, swelling, pain, loss of function |
| Mechanism | Mast cell degranulation and axon reflex | Complex interplay of vascular, cellular, and humoral responses |
| Location | Confined to the local skin surface | Can be local or systemic |
| Purpose | Immediate demonstration of vascular and nerve reactivity | Protective response to eliminate initial cause of cell injury |
Conclusion
The triple response of inflammation is a fundamental concept illustrating how the body's vascular system and peripheral nerves work together in an immediate, protective reaction to injury. While exaggerated in conditions like dermatographism, its components – red line, flare, and wheal – are critical indicators of normal inflammatory and neural function. For health professionals, this simple skin reaction is a valuable tool for assessing allergic sensitivity and peripheral nerve integrity.
For further reading on this topic, a useful resource is the detailed overview provided by ScienceDirect, which discusses the mechanisms in greater detail.
