Prior treatment with small amounts of inner core-region polysaccharides, from different gram negative bacteria, induced profound T cell mediated suppression of the antibody response. Such suppression is due to an expansion of the pool of suppressor T cells (Ts) activated during the course of a normal antibody response to most bacterial polysaccharide antigens. The minimal structure require to induce suppression is a hexa- saccharide composed of glucose, 2 heptoses and 3 KDO residues. Since this structure is conserved among gram negative bacteria, it may represent an important virulence factor, especially when associated with lipid A molecules, e.g. those present in Pseudomonas species, that are unable to abolish the expression of Ts function.
