The mouse monoclonal antibody clone WN1 222-5 recognizes the core region of lipopolysaccharide (LPS), whereas it lacks reactivity with free lipid A and Rd2 or smaller LPS. LPS is a constituent of the outer membrane of the cell wall of certain types of Gram-negative bacteria, such as E. coli, Salmonella, Shigella, Pseudomonas, Neisseria, Haemophilus, and some other lesser known pathogens.