Final answer:
Toll-like receptors (TLRs) are membrane-bound, integral to the cell surface receptors on immune cells, and play a significant role in the immune system by recognizing pathogenic molecules.
Step-by-step explanation:
Toll-like receptors (TLRs) are an essential component of the immune system, known as pattern recognition receptors (PRRs) that play a key role in detecting pathogens and activating immune responses. These receptors recognize molecules characteristic of broad classes of pathogens, such as pathogen-associated molecular patterns (PAMPs). TLRs are not cytosolic; rather, they are membrane-bound proteins localized on the cell surface of immune cells, such as phagocytes. They are a sort of cell-surface receptor and are integral to the plasma membrane. These transmembrane receptors facilitate signal transduction by converting extracellular signals into intracellular ones without requiring the ligands to enter the cell.