Toll-like receptors (TLRs) can be found ______ of macrophages.

• A. only in the nucleus
• B. only on the plasma membrane
• C. on the surface and within endosomal membranes
• D. exclusively in the cytoplasm

Answer: (C)

Verified step by step guidance

1. Understand that Toll-like receptors (TLRs) are a class of proteins that play a key role in the innate immune system by recognizing pathogen-associated molecular patterns (PAMPs).
2. Recall that TLRs are located in different cellular compartments depending on the type of ligand they recognize: some detect extracellular pathogens, while others detect nucleic acids from viruses inside the cell.
3. Recognize that TLRs can be found both on the plasma membrane (surface) to detect bacterial components like lipopolysaccharides, and within endosomal membranes to detect viral and bacterial nucleic acids.
4. Eliminate options that are incorrect based on this knowledge: TLRs are not only in the nucleus, nor exclusively in the cytoplasm, and not only on the plasma membrane.
5. Conclude that the correct location of TLRs in macrophages is both on the surface (plasma membrane) and within endosomal membranes, allowing them to detect a broad range of pathogens.