Immunogenicity of cytolipin H aggregated with Acholeplasma laidlawii membrane proteins.

Abstract

The list of immunologically active lipids found in membranes of normal and malignant cells is growing steadily since the isolation of cardiolipin in 1942 and of cytolipin H in 1958 (1, 2). The purified lipids usually function as haptens, failing to elicit an antibody response when injected into animals (2). Antisera to the lipid haptens have, therefore, been prepared either by injection of tissue fractions or of the purified lipids mixed with protein of a different species. Both methods are not completely satisfactory as tissue fractions may contain several serologically active lipids resulting in sera of low specificity, and the injection of the purified lipid hapten mixed with swine serum or albumin and adjuant frequently fails to elicit a good antibody response to the lipid (2). A new approach to the preparation of antibodies to lipid haptens has recently been proposed by us (3). Purified glycolipid haptens of Mycoplasma pneumoniae were bound to membrane proteins of Acholeplasma laidlawii by a reaggregation process (4) which consisted of solubilization of lipid-depleted A. laidlawii membranes and M. pneumoniae glycolipids in 20 mM sodium dodecyl sulfate (SDS) followed by dialysis of the mixed solutions against 20 mM Mg2+ . The reaggregated material elicited the production in rabbits of antibodies which fixed complement and precipitated the purified glycolipids (3, 5). Free glycolipids or their mixture with A. laidlawii membrane proteins were far less effective in evoking these antibodies (3). The main advantage in utilizing hybrid reaggregates consisting of protein and lipid derived from membranes of two different organisms lies in the ability to select the lipid and the protein components of the reaggregate and thus control the type of antibodies produced. The reaggregation process seems to involve an intimate binding of lipid to protein, presumably by the same kind of bonds responsible for their association in biological membranes.