Factor present in final common terminal complement pathway is rpt Q 38

**Core Concept**
The final common terminal complement pathway involves the formation of the Membrane Attack Complex (MAC), which leads to cell lysis and death. This pathway is crucial in the immune response, particularly in the defense against bacterial and viral infections.

**Why the Correct Answer is Right**
The correct answer is C, C5b-9. This is because the MAC, also known as the terminal complement complex, is formed by the sequential activation of C5b, C6, C7, C8, and multiple molecules of C9. The C5b-9 complex inserts into the target cell membrane, creating a pore that disrupts cell function and ultimately leads to cell lysis. This is the final step in the complement cascade, which is essential for eliminating pathogens.

**Why Each Wrong Option is Incorrect**
* **Option A:** This is incorrect because it does not describe the terminal complement complex. C3 is an important component of the complement cascade, but it is not the correct answer for this question.
* **Option B:** This is incorrect because it is a protein involved in the coagulation pathway, not the complement pathway. Factor B is a component of the alternative complement pathway, but it is not the correct answer for this question.

**Clinical Pearl / High-Yield Fact**
The complement system plays a crucial role in the elimination of pathogens, and its dysregulation can lead to autoimmune diseases such as systemic lupus erythematosus (SLE). Understanding the complement cascade is essential for diagnosing and treating these conditions.

**Correct Answer: C. C5b-9**