Presentation of an MuLV-related tumour antigen in liposomes as a potent tertiary immunogen after adoptive transfer.

International audienceThe immunogenicity of Gross virus cell surface antigen (GCSAa) extracted from rat lymphoma cells can be dramatically increased by its presentation into liposomes, probably by mimicking the cell membrane presentation. Induction of an anti-GCSAa secondary antibody response has been found to require the use of liposomes as GCSAa vehicle for both the priming and the boosting immunizations. In order to investigate the sensitivity of highly immune cells to the liposome presentation, immune spleen cells were stimulated in vitro with either soluble GCSAa or GCSAa-liposomes and transferred together with the immunogen into syngeneic animals. Only spleen cells from high responders, which have been immunized twice with GCSAa-liposomes, were able to generate an antibody response in naive recipients after their restimulation with the GCSAa-liposome preparation. Their restimulation with soluble antigen was ineffective unless 10% peritoneal exudate cells (PEC) from naive rats were added during the in vitro incubation. Stimulation with GCSAa-liposomes was further improved by the addition of 10% PEC. Macrophages were found to play a central role in the induction of antibody response in the recipients after stimulation with GCSAa-liposomes. Treatment of immune spleen cells with the macrophage-killing agent leucine methyl ester prior their restimulation in vitro with GCSA-liposomes in the absence of PEC, or depletion of macrophage after their in vitro incubation with this immunogen, completely abolished the induction of anti-GCSAa antibodies in the recipients

In vitro cellular immune response to measles viral glycoproteins: role of the antigen vector.

International audienceThe capacity of measles virus and haemagglutinin (HA) and fusion (F) glycoproteins, presented either as soluble antigens, associated with liposomes or as Iscoms, to induce an in vitro primary and anamnestic cellular response was studied in syngeneic W/Fu rats using the MTT colorimetric assay. A primary cellular response was observed when the virus, HA + F liposomes or HA + F Iscoms were used as immunogens, but not when soluble HA + F glycoproteins were used. The irradiation of the naïve spleen cells at 500 rads allowed the generation of a primary response with the soluble antigens. All these primary responses were low, of similar intensity and dose-dependent. The responses were stronger after the stimulation of spleen cells from seropositive immune rats with virus, HA + F liposomes or HA + F Iscoms, whereas they were moderate after stimulation with soluble HA + F. In addition, far less antigenic material was required and the use of a vehicle for HA + F (liposomes, Iscoms) dramatically lowered the threshold of the sensitivity to the antigens. The immunization of rats with soluble HA + F glycoproteins resulted in the anergy of their spleen cells even to virus, HA + F liposomes or HA + F Iscoms. Again, irradiation of these cells could restore their ability to elicit a primary response to any type of HA + F immunogens. Using the lysosomotropic Leu-0-Met agent, all the cellular responses were found to be accessory cells dependent, the responses being restored after supplementation with 10% peritoneal exudate cells from naïve rats. These treatments did not break the immunosuppression induced by soluble HA + F glycoproteins. The uptake of the various immunogens by the murine macrophage cell line J774-1 was also studied using radioactively labelled virus and HA + F glycoproteins. The uptake of soluble HA + F was limited to 10-15%, whereas that of the other immunogens was almost complete. The data reported indicate that the modification of the supramolecular architecture of HA + F glycoproteins by their presentation in liposomes or Iscoms could modulate their immunogenicity, both qualitatively and quantitatively. It could prevent the generation of a radiosensitive suppressive mechanism, increase the sensitivity to the antigen and the activation level of the responding cell population. Quantitative modifications are accessory cell dependent and initiated within the first hour of the stimulation

Phase separation of miscible phospholipids by sonication of bilayer vesicles.

Sonication of phospholipid vesicles may result, according to their liquid or solid crystal state, in the generation of unilamellar vesicles or structural defects within their bilayers, respectively. The transition temperature Tm of the phospholipid bilayer is usually the threshold temperature delineating the physical effects of ultrasound. However, for vesicles made from a mixture of two miscible phospholipids, this threshold temperature was not found to be the intermediate Tm of the phospholipid mixture bilayers, but the Tm of the lowest melting component. This was due to a simultaneous lateral phase separation of the two phospholipids induced by the sonication as demonstrated by differential scanning calorimetry analysis