The IgG subclass responses to antigens incorporated in liposomes conta
ining lipid A were investigated using a synthetic malarial antigen (SP
f66) and cholera toxin (CT). The antigen-specific IgG subclass respons
e was determined in BALB/c mice immunized with either: (a) SPf66 encap
sulated in liposomes containing lipid A, (b) CVT bound to the surface
of liposomes containing lipid A, or (c) both encapsulated SPf65 and su
rface-bound CT in the same liposomes. In each case the antibodies to S
Pf66, CT and lipid A demonstrated an IgG2a predominance. Liposomes con
taining lipid A not only increased the magnitude of the antibody respo
nse to liposomal antigens but elicited predominantly IgG2a subclass an
tibodies as well.