**Core Concept**
The contraction of endothelial cell cytoskeleton during acute inflammation leads to the opening of intercellular gaps, allowing fluid and leukocytes to pass through. This process is mediated by the reorganization of actin filaments and the contraction of the endothelial cell cytoskeleton.

**Why the Correct Answer is Right**
During acute inflammation, the endothelial cells lining the blood vessels undergo a series of changes in response to inflammatory mediators. One of the key changes is the contraction of the endothelial cell cytoskeleton, which is mediated by the reorganization of actin filaments. This contraction leads to the opening of intercellular gaps, allowing fluid and leukocytes to pass through the endothelial layer. The contraction of the endothelial cell cytoskeleton is a crucial step in the inflammatory process, allowing for the migration of leukocytes into the affected tissue.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the contraction of endothelial cell cytoskeleton does not lead to the formation of new blood vessels.

**Option B:** This option is incorrect because the contraction of endothelial cell cytoskeleton does not lead to the breakdown of the blood-brain barrier.

**Option C:** This option is incorrect because the contraction of endothelial cell cytoskeleton does not lead to the activation of the complement system.

**Clinical Pearl / High-Yield Fact**
The contraction of the endothelial cell cytoskeleton is a critical step in the inflammatory process, allowing for the migration of leukocytes into the affected tissue. This process is mediated by the reorganization of actin filaments and the contraction of the endothelial cell cytoskeleton.

**Correct Answer:** C. Increased permeability