**Core Concept**
Toll-like receptors (TLRs) are a family of pattern recognition receptors (PRRs) that play a crucial role in the innate immune response. They recognize pathogen-associated molecular patterns (PAMPs) derived from various microorganisms, triggering an inflammatory response to eliminate the invading pathogens. TLRs are expressed on various cell types, including immune cells and non-immune cells.

**Why the Correct Answer is Right**
The correct answer involves the expression of TLRs on antigen-presenting cells (APCs), such as dendritic cells and macrophages. These APCs express TLRs on their surface, allowing them to recognize PAMPs and initiate an immune response. Upon recognition, TLRs activate downstream signaling pathways, leading to the production of pro-inflammatory cytokines and the activation of adaptive immune responses. The expression of TLRs on APCs enables them to phagocytose and eliminate pathogens, while also presenting antigens to T-cells for further immune activation.

**Why Each Wrong Option is Incorrect**
* **Option A:** TLRs are not typically expressed on epithelial cells, which form a barrier against pathogens but do not actively participate in immune recognition.
* **Option B:** Neurons do express some PRRs, but they are not primarily responsible for recognizing PAMPs and initiating an immune response.
* **Option C:** While endothelial cells can express some TLRs, they are not the primary cell type responsible for recognizing PAMPs and initiating an immune response.

**Clinical Pearl / High-Yield Fact**
TLRs are essential for recognizing and responding to pathogens, but their activation can also lead to excessive inflammation and tissue damage. Therefore, it is crucial to modulate TLR signaling pathways to prevent excessive immune responses, which can contribute to various inflammatory and autoimmune diseases.

**Correct Answer: D. Dendritic cells and macrophages.**