INABILITY OF THE FRANCISELLA-TULARENSIS LIPOPOLYSACCHARIDE TO MIMIC OR TO ANTAGONIZE THE INDUCTION OF CELL ACTIVATION BY ENDOTOXINS

We studied the ability of the lipopolysaccharide (LPS) extracted from a vaccine strain of Francisella tularensis (LPS-Ft) to mimic LPSs from other gram-negative bacteria for activation of various murine cell ty pes or to antagonize the effects of other LPSs. We found that activati on of macrophages for the production of tumor necrosis factor alpha an d NO, of pre-B lymphocytes for the expression of surface immunoglobuli ns, and of bone marrow cells for the expression of LPS-binding sites w as either undetectable with LPS-Ft or required concentrations 100 to 1 ,000 times higher than for standard LPSs. Preexposure of macrophages t o LPS-Ft also failed to trigger down-regulation of tumor necrosis fact or alpha (desensitization) or up-regulation of NO responses to an endo toxin challenge. In contrast to other atypical LPSs, LPS-Ft was also u nable to antagonize any of the endotoxin-induced cellular responses me ntioned above, suggesting that this LPS does not interact with LPS rec eptors.