Liposome stimulation of anti-BSA antibody production in mice

Accurate determination of adjuvant-associated protein or peptide by ninhydrin assay

Modern peptide and subunit vaccines are increasingly having to rely on the use of immunological adjuvants to achieve effective immunity. However, the only adjuvant currently approved for use in humans is aluminium hydroxide, although many adjuvants are currently under preclinical development. Determining immunogen concentration in the presence of adjuvants such as aluminium hydroxide gel, liposomes or NISV has proved to be problematic. One approach has been to use radiolabelled antigens to extrapolate concentration to a preparation using native immunogen. However, the use of a colorimetric assay would allow greater flexibility in terms of immunogen used and would reduce costs and remove safety problems. Of the colorimetric methods we have examined thus far, only the manual ninhydrin assay has produced consistent results with detection of microgram quantities of protein or peptide in the presence of NISV or Alhydrogel, but not liposomes. As the assay relies on the detection of free amino groups after protein hydrolysis, peptides as well as proteins may be effectively determined irrespective of amino acid composition, a considerable advantage over other colorimetric assay systems.

Studies on the adjuvant activity of non-ionic surfactant vesicles: adjuvant-driven IgG2a production independent of MHC control

The ability of non-ionic surfactant vesicles (NISV) to stimulate humoral responses to bovine serum albumin (BSA) in H-2b, H-2d and H-2k congenic mice on the Balb genetic background was compared with that of Freund's complete adjuvant (FCA). After two subcutaneous inoculations of BSA formulated in each adjuvant, the NISV preparation was found to stimulate significantly higher total antibody production than FCA in mice carrying the H-2b haplotype at all time points measured after secondary inoculation (2, 5 and 10 weeks) and in Balb/c mice (H-2d) at two weeks after inoculation. Both adjuvants were found to overcome the apparent non-responsiveness of Balb/B mice (H-2b) to BSA alone. Analysis of the IgG subclass responses to BSA revealed a pattern of IgG1 but not IgG2a production similar to that for whole immunoglobulin. IgG1 responses invariably differed significantly, not only between adjuvant formulations but also between different H-2 haplotypes receiving the same inoculation. On the other hand, IgG2a responses did not differ significantly between H-2 haplotypes in animals given the same adjuvant preparations, although they did differ significantly in mice given BSA alone. Therefore, these results suggest that adjuvants cannot only circumvent antigen-specific non-responsiveness or low responsiveness, but also can induce antibody isotype switching independent of major histocompatibility complex controls.

Enhancement of in vivo and in vitro T cell response against measles virus haemagglutinin after its incorporation into liposomes: effect of the phospholipid composition

Artificial phospholipid bilayer vesicles were tested for their capacity to enhance the priming and the restimulation of mouse T cells against the haemagglutinin (H) glycoprotein of the measles virus in vivo and in vitro. H glycoprotein was purified and incorporated into liposomes made of cholesterol, dicetylphosphate and dilauroylphosphatidylcholine (DLPC) or distearoylphosphatidylcholine (DSPC). H in DLPC or DSPC-liposomes was found to be a potent in vivo stimulator of lymph node T cells harvested from mice immunized with measles virus, whereas H glycoprotein in free form did not elicit any proliferative T cell response. When used to immunize naive mice, only H in DSPC-liposomes was able to prime T cells as evidenced by the capacity of lymph node cells to proliferate in the presence of H in liposomes or measles virus as secondary stimulating agents in vitro. H-specific T cell clones derived from animals immunized with H in DSPC-liposomes were able to recognize H glycoprotein both in free form and incorporated into liposomes in the presence of naive spleen cells as APC. However, compared with the liposome forms, 20-fold more H protein in free form was required to elicit a T cell clone response at a similar level. This liposome immune enhancing effect on the T cell clone recognition of H glycoprotein was also observed when peritoneal exudate cells were used as APC. These data demonstrate that the insertion of a membrane-derived antigen into artificial membranes may be a prerequisite for the priming and stimulation of specific T cells both in vivo and in vitro. In addition, the nature of the phospholipid used to build the liposomes appears to be a critical parameter.

Antibody responses to liposome-associated antigen

The humoral antibody response of CAF1 mice to low doses (1-100 micrograms) of egg albumin (EA) encapsulated in or covalently bound to the surface of liposomes was studied for three routes of administration. The liposome immunoadjuvant effect observed was found to depend on the location of the antigen, either on the liposome surface or entrapped inside the liposome, and on the number of immunizations. Following a single immunization, the highest antibody titers were elicited with liposomes having EA conjugated to their surface, regardless of the route of administration. For multiple immunizations given i.v. or i.p. EA conjugated to the surface of liposomes was also superior to either free or liposome-encapsulated EA. However, the antibody response to EA bound to the surface of liposomes was not enhanced as compared to free EA following multiple subcutaneous immunizations.

Liposome as an adjuvant for the production of estradiol antibodies

Mice immunized with liposome associated estradiol-bovine serum albumin conjugate (E2-BSA) showed a significantly higher estradiol-specific immune response than did mice injected with the free conjugate. The conjugation of estradiol with BSA is imperative, since injection of liposomes with estradiol in the lipid bilayer was found to be ineffective in inducing an immune response. Entrapment of E2-BSA in neutral and positively charged liposomes was found to be a potent mode of immunostimulation, even better than emulsification in complete Freund's adjuvant (CFA). Covalent liposome surface association of E2-BSA induced a good immunopotentiation. However, the response was lower than that observed with the entrapped conjugate. The affinity and the specificity of antisera, raised in different ways, were determined.

Induction of hapten-specific lymphoid cell proliferation by liposome-carrying molecules from haptenated epidermal cells in contact sensitivity

Liposomes containing the extract of trinitrophenylated (TNP) epidermal cells stimulated lymph node cells from TNCB-sensitized mice effectively. Optimal stimulation was achieved by the liposome containing 0.06 microgram of the extract of TNP epidermal cells/microgram of phospholipid at a concentration of 20 micrograms phospholipid/ml. The response was hapten-specific and macrophage-dependent. UV irradiation of the epidermal cells abolished their ability to stimulate the lymph node cells. Furthermore, the liposomes containing the extract of TNP epidermal cells treated with anti-Ia and complement failed to stimulate the lymph node cells. The liposomes recovered their reactivity when nonhaptenated Ia antigen-rich epidermal extract was added. Taken together, it is likely that haptenated molecules and Ia antigen on the liposome stimulated T-lymphocytes in the presence of macrophages.

The effect of surface charges of liposomes in immunopotentiation

The purpose of this study was to establish the effect of surface charges of liposomes on its adjuvant activity to an entrapped protein antigen. The immune responses of rabbits immunized subcutaneously with lysozyme entrapped in neutral negatively and positively charged liposomes and compared with complete Freund's adjuvant (CFA), showed positively charged liposomes to be a better adjuvant than neutral, negatively charged liposomes and even CFA. This was true for solid liposomes also. Interestingly, injection of positively charged liposomes led to the formation of granulomas at the sites of immunization, which was not observed with neutral and negatively charged liposomes.