**Core Concept**
The primary function of **Toll-like Receptors (TLRs)** is related to the recognition of **pathogen-associated molecular patterns (PAMPs)**. This recognition is crucial for the initiation of the **innate immune response**. TLRs play a key role in detecting microbial infections.

**Why the Correct Answer is Right**
TLRs recognize PAMPs, such as bacterial lipopolysaccharides, viral RNA, and fungal cell wall components, triggering a signaling cascade that activates the innate immune response. This leads to the production of **cytokines** and **chemokines**, which recruit immune cells to the site of infection. The activation of TLRs also induces the expression of **co-stimulatory molecules** on antigen-presenting cells.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because while TLRs can activate adaptive immunity, their primary function is in the innate immune response.
**Option B:** Incorrect as it is not directly related to the primary function of TLRs.
**Option C:** Incorrect because, although TLRs can influence cell survival, this is not their primary function.

**Clinical Pearl / High-Yield Fact**
Remember, TLRs are critical for the recognition of pathogens and the initiation of the immune response. Dysregulation of TLR signaling can lead to **immune disorders** or **autoimmune diseases**.

**Correct Answer:** D. Recognition of Pathogen