Final answer:
The false statement about TLR4 is that it's an example of a phagocytic receptor. TLR4 is a pattern recognition receptor that detects pathogen-associated molecular patterns but does not directly engulf pathogens.
Step-by-step explanation:
The subject of this question is the Toll-like receptor 4 (TLR4), which is an essential component of the innate immune system. Among the options provided, the statement that is false about TLR4 is 'd. TLR4 is an example of a phagocytic receptor.' TLR4 indeed has a key role in immune response, but it is not classified as a phagocytic receptor. Instead, phagocytic receptors are involved in the direct engulfment and metabolism of pathogens, whereas TLRs, including TLR4, are pattern recognition receptors (PRRs) that primarily mediate the recognition of pathogen-associated molecular patterns (PAMPs) such as lipopolysaccharide (LPS).
LPS is indeed the ligand for TLR4, and upon ligand binding, TLR4 homodimerizes and undergoes conformational changes that lead to the activation of its intracellular domain. This intracellular domain is known as the Toll/IL-1 receptor (TIR) domain. Furthermore, TLR4 is not a solitary component; it cooperates with accessory proteins such as MD2, which associates with the extracellular domain of TLR4 to recognize LPS.