**Question:** Complement responsible for activation of bacterial lysis is:

A. Complement C3b
B. Complement C5a
C. Complement C6
D. Complement C7

**Core Concept:** Complement is a part of the immune system that plays a critical role in defending the body against pathogens, particularly bacteria. The complement system comprises a series of proteins that interact with each other to form a cascade, culminating in the destruction of pathogens. Complement activation leads to the formation of various effector molecules, such as C3b, C5a, C6, and C7, which contribute to the process of bacterial lysis.

**Why the Correct Answer is Right:** Complement C3b is responsible for the activation of bacterial lysis because it binds to the bacterial surface, marking it for destruction by the phagocytic cells (e.g., macrophages and neutrophils). Once bound, the bacterial surface becomes more recognizable to these immune cells, enhancing their ability to engulf and eliminate the pathogen.

**Why Each Wrong Option is Incorrect:**

A. Complement C5a (Option B) is a potent anaphylatoxin that promotes inflammation, chemotaxis, and activation of phagocytes, but it does not directly participate in bacterial lysis.
B. Complement C6 (Option C) is a critical component of the complement system but does not directly activate bacterial lysis.
D. Complement C7 (Option D) is involved in the formation of the membrane attack complex (MAC), which helps to lyse bacteria, but it is not directly responsible for bacterial lysis.

**Clinical Pearl:** Understanding the role of various complement proteins is crucial for recognizing the complex interplay among different immune components and their functions in combating infections. Knowledge of these processes is essential for optimal patient care, particularly in immunocompromised patients who may rely more heavily on the complement system for defense.