We have previously reported that antigen coupled with liposomes induced antigen-specific and IgE-selective unresponsiveness in mice. This antigen preparation was investigated for application in a novel vaccine protocol to induce minimal IgE synthesis. In this study, ovalbumin (OVA)-liposome conjugates were made using liposomes of four different lipid components, including unsaturated carrier lipid and three different saturated carrier lipids, after which the induction of anti-OVA antibody production was investigated in mice. All of the OVA-liposome conjugates induced IgE-selective unresponsiveness. The membrane fluidity of liposomes, as measured by detecting changes in the fluorescence polarization of a 1,6-diphenyl-1,3,5-hexatriene (DPH) probe located in the bilayers, was significantly higher in liposomes consisting of unsaturated carrier lipids than those of the other liposomes consisting of saturated carrier lipids. The highest titer of anti-OVA IgG was observed in mice immunized with OVA-liposomes made using liposomes consisting of unsaturated carrier lipids. In addition, among these OVA-liposomes, the one possessing the longest carbon chain induced the lowest IgG antibody production. These results suggest that the membrane fluidity of liposomes might affect the adjuvant effect of liposomes but not the induction of IgE-selective unresponsiveness in immunizations with surface-linked liposomal antigens.

We have previously reported that purified Shiga–like toxins (SLT), SLT–I and SLT–II coupled with liposomes induced a substantial amount of anti–SLT–I and anti–SLT–II IgG antibody production, respectively, in mice. The levels of anti–SLT antibody in the sera of SLT–liposome–immune mice correlated well with the protection against subsequent challenge with SLT. In this study, mice were immunized intraperitoneally with the mixture of SLT–I–liposome and SLT–II–liposome and protection against oral infection with cytotoxin–producing Escherichia coli O157:H7 was evaluated. All of the mice that received immunization with the mixture of SLT–I–liposome and SLT–II–liposome were protected against subsequent intravenous challenge with 10 LD₅₀ of either SLT–I or SLT–II. Eight weeks after primary immunization, mice were inoculated intragastrically with 10⁹ CFU of E. coli O157:H7 strain 96–60. All SLT–liposome–immune mice tested survived without any apparent symptom while control mice died within 5 days. In addition, as shown by other antigen–liposome conjugates, SLT–liposome induced undetectable anti–SLT IgE antibody production while they induced substantial amounts of anti–SLT IgG antibodies. These results suggest that SLT–liposome conjugate may serve as a candidate vaccine that induces protection against cytotoxin–producing E. coli infection.

Background: We have previously reported that ovalbumin (OVA) coupled with liposome via glutaraldehyde (GA) induced OVA–specific– and IgE–selective unresponsiveness in mice. Methods: In this study, OVA–liposome conjugates were made using four different coupling protocols: via GA, N–(6–maleimidocaproyloxy) succinimide (EMCS), disuccinimidyl suberate (DSS) and N–succimidyl–3(2–pyridyldithio)propionate (SPDP) and the induction of antigen–specific IgG and IgE antibody production was investigated for each. In addition, antigen–specific cytokine production by spleen cells of mice immunized either with OVA–liposome or with OVA adsorbed with aluminum hydroxide was investigated. Results: OVA–liposome conjugates coupled via GA or DSS did not induce anti–OVA IgE antibody production but induced substantial anti–OVA IgG antibody production. On the other hand, the induction of anti–OVA IgE unresponsiveness by OVA–liposome conjugates coupled via EMCS or SPDP was incomplete. The amount of interleukin 4 (IL–4) produced by spleen cells stimulated in vitro with OVA correlated well with anti–OVA IgE antibody production in donor mice. However, the production of no other cytokine, i.e., IL–2, IL–5, IL–10 or interferon–γ, was correlated with in vivo IgE antibody production. Conclusion: OVA–liposome coupled via GA or DSS induced complete suppression of anti–OVA IgE production. The results in this study further suggest that the regulation of IgE antibody production does not neccessarily correlate with so–called Th1 cytokine production.