Production and characterisation of mouse monoclonal antibodies reacting with the lipopolysaccharide core region of gram-negative bacilli.

Monoclonal antibodies to the lipopolysaccharide (LPS) core region were produced by immunising mice with Escherichia coli strain J5 (chemotype Rc). One of these bound to the deepest part of the core, i.e., Lipid A, and reacted with other heat-killed but not live gram-negative bacilli, including E. coli, Klebsiella pneumoniae and Pseudomonas aeruginosa. Eight other monoclonal antibodies, binding to the terminal glucose residue of Rc LPS, reacted with live cells of E. coli strains only. Thus, the O antigen does not necessarily render the core inaccessible to antibody. However, despite binding to live bacteria, these monoclonal antibodies neither enhanced phagocytic killing, nor protected mice from dying from gram-negative infection or endotoxaemia. It is concluded that antibodies reacting with the most immunodominant parts of the J5 core are not protective.