Membrane attack complex is –
**Core Concept**
Membrane attack complex (MAC) is a critical component of the complement system, a group of proteins that play a vital role in the innate immune response. The MAC is responsible for forming pores in the cell membrane of target cells, leading to cell lysis and death.
**Why the Correct Answer is Right**
The MAC is formed through the assembly of C5b, C6, C7, C8, and multiple C9 molecules. This process creates a complex that inserts into the target cell membrane, forming a pore that disrupts the cell's osmotic balance and ultimately leads to cell death. The MAC is particularly effective against gram-negative bacteria, which have an outer membrane that provides an additional target for the complex.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not accurately describe the membrane attack complex. The correct description of MAC is a critical component of the complement system.
**Option B:** This option is incorrect because it refers to a different protein complex involved in cell signaling, not cell lysis.
**Option C:** This option is incorrect because it describes a type of immune response, not a specific protein complex.
**Clinical Pearl / High-Yield Fact**
The membrane attack complex is a key component of the innate immune response and plays a critical role in protecting against gram-negative bacterial infections. Understanding the role of MAC in the complement system is essential for appreciating the complex interplay between the innate and adaptive immune responses.
**Correct Answer:** C.