**5. Lipopolysaccarides of uropathogenic** *Escherichia coli*

Lipopolysaccharide (LPS) is a major part of the cell wall which has highly conserved lipid A-core and repeating O-antigen subunits which vary in different strains of *E. coli* depending on the sugar residues and their linkage patterns within the repeating subunits [41, 65]. LPS is very prominent in activating the host immune response and the stimulation of nitric oxide and cytokine (IL-1, TNF-α) for inflammatory response [11, 66]. Also, it triggers the production of specific antibodies to the somatic antigen and the humoral immune response to other antigens of the pathogen [31]. Several antigenic types of LPS help UPEC to escape being killed by the host serum [31]. A study on animal models has reported that LPS-associated acute renal failure is due to the response of the host to the LPS and not based on the expression of TLR4 (LPS receptor) in the kidney [66].
