**Core Concept**
Increased permeability in acute inflammation is a critical early event that allows fluid and inflammatory cells to move into the affected tissue. This process is mediated by various factors, including the contraction of endothelial cells and the release of chemical mediators.

**Why the Correct Answer is Right**
Increased permeability in acute inflammation is primarily due to the contraction of endothelial cells and the release of chemical mediators such as histamine and bradykinin. These molecules cause the contraction of endothelial cells, leading to the widening of intercellular junctions and increased permeability. Additionally, cytokines such as TNF-alpha and IL-1 also contribute to increased permeability by promoting the expression of adhesion molecules on endothelial cells.

**Why Each Wrong Option is Incorrect**
**Option A:** Cell contraction is indeed a key factor in increased permeability, as it leads to the widening of intercellular junctions and increased fluid movement across the endothelium. Therefore, this option is incorrect because it is actually a correct mechanism of increased permeability.
**Option B:** Endothelial injury can also contribute to increased permeability by disrupting the integrity of the endothelial layer and allowing fluid and inflammatory cells to move into the affected tissue.
**Option D:** Cytokines, such as TNF-alpha and IL-1, also play a significant role in increased permeability by promoting the expression of adhesion molecules on endothelial cells.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that increased permeability in acute inflammation is a reversible process that can be reversed by the removal of chemical mediators and the restoration of endothelial cell contraction.

**✓ Correct Answer: C. Lytic enzymes**