Adjuvant activity of non-ionic block copolymers. V. Modulation of antibody isotype by lipopolysaccharides, lipid A and precursors.

Non-ionic block copolymers and lipopolysaccharides are both effective immunological adjuvants which are thought to act via distinct mechanisms. We hypothesized that they might produce synergistic effects when used together. We prepared a series of lipopolysaccharide (LPS) preparations ranging from the smallest precursor, lipid X through complete LPS with O-polysaccharide chains. Three preparations with reduced toxicity, monophosphoryl lipid A, partially hydrolysed Ra-LPS and LPS of Rhodopseudomonas sphaeroides were also utilized. All LPS preparations except the smallest were effective adjuvants for inducing early antibody responses to trinitrophenyl-conjugated hen egg albumin (TNP-HEA) when injected in squalane-in-water emulsions with copolymer L141. Only the larger LPS preparations induced sustained antibody responses. By itself, emulsions of copolymer L141 induced a predominant IgG1 antibody isotype response with lesser amounts of IgG2a and IgG2b. Surprisingly, all of the LPS preparations tested increased the proportion of IgG2 isotypes even though some had little effect on overall titres. The detoxified Ra-LPS (Ra-detox) was the most effective preparation for both increasing antibody titres and inducing the desirable IgG2a and IgG2b isotypes. These results demonstrate that the combination of LPS and block polymer adjuvants can produce synergistic effects without unacceptable toxicities.