Induction and detection of antibodies to squalene.

An enzyme-linked immunosorbent assay (ELISA) utilizing antigen coated on hydrophobic polyvinyldiene fluoride (PVDF) membranes is described for detecting antibodies that bind to squalene (SQE). Because of the prior lack of availability of validated antibodies to SQE, positive controls for the assay were made by immunization with formulations containing SQE to create monoclonal antibodies (mAbs) that reacted with SQE. Among eight immunogens tested, only two induced detectable murine antibodies to SQE: liposomes containing dimyristoyl phosphatidylcholine, dimyristoyl phosphatidylglycerol, 71% SQE, and lipid A [L(71% SQE+LA)], and, to a much lesser extent, an oil-in-water emulsion containing SQE, Tween 80, Span 85, and lipid A. In each case, lipid A served as an adjuvant, but neither SQE alone, SQE mixed with lipid A, liposomes containing 43% SQE and lipid A, nor several other emulsions containing both SQE and lipid A, induced antibodies that reacted with SQE. Monoclonal antibodies produced after immunizing mice with [L(71% SQE+LA)] served as positive controls for developing the ELISA. Monoclonal antibodies were produced that either recognized SQE alone but did not recognize squalane (SQA, the hydrogenated form of SQE), or that recognized both SQE and SQA. As found previously with other liposomal lipid antigens, liposomes containing lipid A also induced antibodies that reacted with the liposomal phospholipids. However, mAbs were also identified that reacted with SQE on PVDF membranes, but did not recognize either SQA or liposomal phospholipid. The polyclonal antiserum produced by immunizing mice with [L(71% SQE+LA)] therefore contained a mixed population of antibody specificities and, as expected, the ELISA of polyclonal antiserum with PVDF membranes detected antibodies both to SQE and SQA. We conclude that SQE is a weak antigen, but that antibodies that specifically bind to SQE can be readily induced by immunization with [L(71% SQE+LA)] and detected by ELISA with PVDF membranes coated with SQE.