Question

Increased vascular permeability in acute inflammation is mainly due to which mediator?

• A. Histamine
• B. IL-2
• C. TGF-beta
• D. FGF

Hint:

Which preformed mast-cell mediator causes the immediate transient venular leak?

Answer 1

The Correct Option is A

Step 1: The question asks what opens up the vessel wall early in acute inflammation. The leakiness comes mostly from venular endothelial cells contracting and pulling apart, leaving interendothelial gaps within minutes of injury.

Step 2: Identify the agent that triggers this contraction fastest. Histamine, stored preformed in mast cell granules, is liberated almost instantly on stimulation and binds H1 receptors on venular endothelium to cause the immediate transient leak. Bradykinin and leukotrienes assist, while IL-1, TNF and IFN-gamma act in a somewhat delayed, longer-lasting fashion.

Step 3: Eliminate the others. IL-2 belongs to lymphocyte activation, TGF-beta drives fibrosis and dampens inflammation, and FGF stimulates new vessel and fibroblast growth during healing. None produce the early permeability spike.

Step 4: The preformed, rapid-acting mediator is therefore histamine.

\[\boxed{\text{Histamine}}\]