COMPARISON OF CONJUGATES COMPOSED OF LIPOPOLYSACCHARIDE FROM SHIGELLA-FLEXNERI TYPE-2A DETOXIFIED BY 2 METHODS AND BOUND TO TETANUS TOXOID

Shigella flexneri type 2a lipopolysaccharide (LPS) nas detoxified with acetic acid (O-SP) or with hydrazine (DeALPS). DeALPS, but not O-SP, retained part of its lipid A. Both gave an identical line of precipita tion with typing antiserum by double immunodiffusion, and both had low levels of LPS activity by the Limulus amoebocyte lysate assay. O-SP h ad an M(r); of similar to 17,000. DeALPS had two components of MS simi lar to 30,00 (major) and similar to 10,000 (minor). Adipic acid hydraz ide derivatives of O-SP and DeALPS were conjugated to tetanus toxoid ( TT), purified by gel filtration through CL-6B Sepharose, and designate d O-SP-TT and DeALPS-TT, respectively. Saccharide (2.5 mu g) as O-SP, DeALPS, or their conjugates was injected subcutaneously into 5-week-ol d mice three times 2 weeks apart. The mice were bled before the second injection and 7 days after the second and third. O-SP alone did not e licit immunoglobulin M (IgM) or IgG LPS antibodies. DeALPS elicited lo w levels of IgM LPS antibodies after the third injection only. Two of three lots of O-SP-TT induced significant levels of IgM LPS antibodies after the third injection. One O-SP-TT lot elicited IgG LPS antibodie s after the second injection, and all three lots elicited significant levels of IgG after the third. DeALPS-TT induced low levels of anti-LP S IgM and IgG only after the third injection. The geometric mean antib ody titers of both immunoglobulin classes induced by O-SP-TT were high er than those induced by DeALPS-TT. By these criteria, O-SP provided a more immunogenic saccharide than DeALPS for S. flexneri type 2a conju gates.