**Core Concept**
Alpha 1 antitrypsin is a serine protease inhibitor (serpin) that plays a crucial role in the regulation of proteolytic activity, particularly in the lungs. It inhibits the activity of neutrophil elastase, a proteolytic enzyme that can damage lung tissue.

**Why the Correct Answer is Right**
Alpha 1 antitrypsin deficiency is a genetic disorder that leads to an imbalance between the proteolytic activity of neutrophil elastase and the inhibitory activity of alpha 1 antitrypsin. This imbalance can result in the destruction of lung tissue, leading to conditions such as chronic obstructive pulmonary disease (COPD) and emphysema. Alpha 1 antitrypsin also has a role in protecting against liver disease, as the deficient protein can accumulate in the liver and cause damage.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as alpha 1 antitrypsin is not primarily involved in the regulation of blood pressure.
**Option B:** This option is incorrect as alpha 1 antitrypsin is not a component of the complement system.
**Option C:** This option is incorrect as alpha 1 antitrypsin is not a pro-coagulant protein.

**Clinical Pearl / High-Yield Fact**
Alpha 1 antitrypsin deficiency is an autosomal co-dominant disorder, meaning that individuals who inherit one copy of the mutated gene (heterozygous) can still develop symptoms, although they are typically milder than those seen in homozygous individuals.

**Correct Answer:** C. Alpha 1 antitrypsin is primarily involved in protecting against lung damage caused by neutrophil elastase.