Timing affects the efficacy of LDL immunization on atherosclerotic lesions in apo E (−/−) mice

Background: Immunization of animals with LDL reduces atherosclerosis. However, whether the timing of immunization affects its efficacy is not known. In this study, we evaluated the influence of timing of immunization on the athero-protective effects of LDL immunization in apo E (−/−) mice. Methods and results: Hypercholesterolemic apo E (−/−) mice were immunized with native LDL (nLDL) at age of 6–7 weeks old or at 20 weeks old. Compared to adjuvant group, mice that were immunized at the age of 6–7 weeks developed significantly smaller aortic sinus plaques with reduced gelatinolytic activity and increased collagen content. This was associated with an increase of oxidized LDL (oxLDL) antibody titer and a marked decrease in splenic IL-4 mRNA expression. Immunization at 20 weeks of age also increased oxLDL antibody titer but did not reduce plaque size, gelatinolytic activity or collagen content but resulted in a modest decrease in macrophage infiltration. Late immunization did not alter splenic IL-4 mRNA expression. Conclusions: Our findings demonstrate that, only early nLDL immunization modulates humoral and cellular immune responses and affects plaques size and composition in apo E (−/−) mice, indicating the critical importance of timing of immunization for its antiatherogenic efficacy.