Characterization of immunogenic properties of haptenated liposomal model membranes in mice. IV. induction of IgM memory

Abstract

This paper describes the induction of IgM immune memory to haptenated liposomes in mice. The tripeptide-enlarged haptens 3-(p-azo-benzenearsonate)-N-acetyl-L-tyrosylglycylglycine (A) and N-(2,4-dinitrophenyl)-β-alanylglycylglycine (J) were coupled to phosphatidylethanolamine (PE) and the conjugates A-PE and J-PE were incorporated into separate liposomal membranes (monofunctional A-PE-liposomes or J-PE-liposomes) or into the same liposomal membranes [bifunctional (A,J)-PE-liposomes]. The magnitude of the humoral response was measured by the appearance of direct and indirect plaque-forming cells in the spleens of immunized mice. Intracutaneous priming of mice with A-PE-liposomes mixed with the adjuvant dimethyl dioctadecyl ammonium bromide (DDA) and secondary immunization with bifunctional (A,J)-PE-liposomes resulted in enhanced hapten A- and J-specific IgM responses. However, no switch from IgM to IgG antibodies was observed in these mice. The J-specific IgM response was enhanced only when hapten J was incorporated into a bifunctional liposome which also contained A-epitopes. In mice primed with A-PE-liposomes in the absence of DDA, a greatly diminished memory to both hapten A and J was observed. This finding indicates a crucial role for the adjuvant in the induction of memory. J-PE-liposomes and DDA were not able to induce memory to monofunctional J-PE-liposomes or bifunctional (A,J)-PE-liposomes. The possibility that hapten A-specific B lymphocytes were responsible for the induction of memory was excluded by hapten-specific blockade of these cells with a B-cell tolerogen. These data, in addition to the observation that no IgM memory could be induced in congenitally athymic nude mice, suggest that the observed memory can be ascribed to priming of hapten A-specific T lymphocytes.