**Question:** Mature defence mechanism is seen in:

A. Innate immunity
B. Acquired immunity
C. Humoral immunity
D. Cell-mediated immunity

**Core Concept:**
The immune system can be divided into two main categories: Innate immunity and Acquired immunity. Innate immunity is the body's first line of defense against pathogens and is characterized by non-specific responses. Acquired immunity, also known as adaptive immunity, is a more specific response developed over time through exposure to antigens.

**Why the Correct Answer is Right:**
The correct answer, "Acquired immunity", represents the mature defense mechanism because it involves the development of a specific immune response against previously encountered pathogens. This response is tailored to the individual and provides long-lasting protection against specific pathogens.

**Why Each Wrong Option is Incorrect:**
A. Innate immunity is the first line of defense and does not involve pathogen-specific responses, making option A incorrect.
B. Innate immunity is not the mature defense mechanism, so option B is incorrect as well.
C. Humoral immunity is a part of Acquired immunity and not a separate defense mechanism, so option C is incorrect.
D. Cell-mediated immunity is also a part of Acquired immunity and not a separate defense mechanism, so option D is incorrect.

**Clinical Pearl / High-Yield Fact:**
The immune system plays a crucial role in defending the body against pathogens. Understanding the distinction between innate and acquired immunity is essential for recognizing and treating infections and diseases effectively.

**Correct Answer:**
D. Cell-mediated immunity (Option D) is a crucial component of Acquired immunity, which is responsible for the mature defense mechanism. However, since all options D, C, B, and A are incorrect, the correct answer to this question is:

**Correct Answer:** D. Immune response involves both innate and acquired immunity.