Liposomal conjugates with plain OVA, Alexa-labeled OVA, or DQ-OVA were prepared essentially in the same way as described previously [22] . Briefly, to a mixture of 90 mg of liposomes and 6 mg of OVA in 2.5 ml phosphate buffer (pH 7.2), 0.5 ml of 2.5% glutaraldehyde solution was added in dropwise fashion. The mixture was stirred gently for 1 h at 37uC, and then 0.5 ml of 3 M glycine-NaOH (pH 7.2) was added to block excess aldehyde groups. This was followed by incubation overnight at 4uC. The liposome-coupled OVA and uncoupled OVA in the resulting solution were separated using CL-4B column chromatography (Pharmacia). The amount of lipid in the liposomal fraction was measured using a phospholipid content assay kit (Wako Pure Chemical). The OVA-liposome solution was adjusted to 10 mg lipid/ml in PBS, sterile-filtered using a Millex-HA syringe filter unit (0.45 mm, Millipore), and kept at 4uC until use.