Impaired stimulation of anti‐bovine serum albumin IgG antibodies by vaccine adjuvants in murine acquired immunodeficiency syndrome

The effect of three adjuvants - alum, N-acetylmuramyl-L-alanyl-D-isoglutamine (MDP), and liposomes - on the IgG antibody isotype response to bovine serum albumin (BSA), was determined in normal and LP-BM5 retrovirus infected C57BL/6 mice. Alum and MDP induced comparable levels of IgG antibodies in normal mice (predominantly IgG1 (greater than 90%)), whereas liposomes induced IgG1 (60%), IgG2a/b (30%) and IgG3 (10%) antibodies. IgG antibody levels using liposomes as adjuvant were five-fold higher than those observed with alum or MDP. Immunization after LP-BM5 infection significantly reduced the effectiveness of alum and MDP, IgG antibody levels being reduced by 80 and 90% at 3 or 7 weeks respectively. The adjuvant activity of liposomes was reduced by 55 and 65% when immunization was started 3 or 7 weeks post LP-BM5 infection. Boosting of pre-immune mice with BSA and alum, MDP or liposomes 3 weeks after LP-BM5 infection showed that, while the magnitude of the antibody response and isotype distribution was not affected, the persistence of the response was severely diminished compared to control, non-infected mice. The reduced immunoadjuvant activity correlated with a reduction in the frequency of splenic Thy1.2+/CD4+ T cells. These results demonstrated that liposomes were more effective than alum or MDP in inducing IgG antibodies, and that immunoadjuvant activity for prophylactic or therapeutic immunization for all 3 adjuvants was significantly impaired by retroviral infections.