This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General pathology, Subject name: Pathology
Which toll like receptors are involved in action of bacterial endotoxins- 
Select and explain. 
A. I, B. II, C. III, D. IV
D: IV
Answer: D: IV 
Explanation: Reference :Robbins basic pathology 9th edition pg no 321:Bacterial endotoxin is a lipopolysaccharide (LPS) that is a component of the outer membrane of gram-negative bac- teria (Fig. 8-2). LPS is composed of a long-chain fatty acid anchor, termed lipid A, connected to a core sugar chain, both of which are very similar in all gram-negative bacteria. Attached to the core sugar is a variable carbohy- drate chain (O antigen), which is used diagnostically to serotype strains of bacteria. Lipid A binds to CD14 on the surface of host leukocytes, and the complex then binds to Toll-like receptor 4 (TLR4), a pattern recognition receptor of the innate immune system that transmits signals that promote cell activation and in ammatory responses.