Hypercholesterolemia Impairs Immunity to Tuberculosis

Abstract

We demonstrate that apolipoprotein E -deficient (ApoE^−/−) mice are highly susceptible to tuberculosis and that their susceptibility depends on the severity of hypercholesterolemia. Wild-type (WT) mice and ApoE^−/− mice fed a low-cholesterol (LC) or high-cholesterol (HC) diet were infected with ∼50 CFU Mycobacterium tuberculosis Erdman by aerosol. ApoE^−/− LC mice were modestly more susceptible to tuberculosis than WT LC mice. In contrast, ApoE^−/− HC mice were extremely susceptible, as evidenced by 100% mortality after 4 weeks with tuberculosis. The lung pathology of ApoE^−/− HC mice was remarkable for giant abscess-like lesions, massive infiltration by granulocytes, elevated inflammatory cytokine production, and a mean bacterial load ∼2 log units higher than that of WT HC mice. Compared to WT HC mice, the gamma interferon response of splenocytes restimulated ex vivo with M. tuberculosis culture filtrate protein was delayed in ApoE^−/− HC mice, and they failed to control M. tuberculosis growth in the lung. OT-II cells adoptively transferred into uninfected ApoE^−/− HC mice had a weak proliferative response to their antigen, indicating impaired priming of the adaptive immune response. Our studies show that ApoE^−/− deficiency is associated with delayed expression of adaptive immunity to tuberculosis caused by defective priming of the adaptive immune response and that elevated serum cholesterol is responsible for this effect.